TS4353/U Owners Manual

TS4353/U Owners Manual
I
TM 09361 A-12
7b&rnntx)
COMMITTED TO EXCELLENCE
PLEASE CHECK FOR CHANGE INFORMATION
AT THE REAR OF THIS MANUAL.
F7523A1 MOD WQ
Distortion Test Set
TS-43531U
OPERATORS
Contract Number: M67854-89-D-0030
NSN: 6625-01-312-2560
Tektronix, Inc.
P.O. Box 500
Beaverton, Oregon 97077
070-7813-01
Product Group 75
Serial Number
First Printing JAN 1991
Copyright.- 1991 Tektronix, Inc. All rights reserved.
Contents of this publication may not be reproduced in
any form without the written permission of Tektronix, Inc.
Products of Tektronix, Inc. and its subsidiaries are
covered by U. S. and foreign patents and/or pending
patents.
^^pNIK
TEKTRONIX, TEK, SCOPE-MOBILE, and
are registered trademarks of Tektronix, Inc.
TELEQUIPMENT is a registered trademark of Tektronix
U.K. Limited.
Printed in U.S.A. Specification and price change
privileges are reserved.
INSTRUMENT SERIAL NUMBERS
Each instrument manufactured by Tektronix has a serial
number pm a panel insert, tag, or stamped on the
chassis. The letter at the beginning of the serial number
designates the country of manufacture. The last five
digits of the serial number are assigned sequentially
and are unique to each instrument. Those manufactured
in the United States have six unique digits. The country
of manufacture is identified as follows:
B010000 —Tektronix, Inc. Beave rt on, Oregon, USA
G100000 —Tektronix Guernsey, Ltd., Channel Islands
E200000 —Tektronix United Kingdom, Ltd., London
J300000 —Sony/Tektronix, Japan
H700000 —Tektronix Holland, NV, Heerenveen, The
Netherlands
Instruments manufactured for Tektronix by external
vendors outside the United States are assigned a two
digit alpha code to identify the country of manufacture
(e.g., JP for Japan, HKfor Hong Kong, ILfor Israel, etc.)
WARRANTY
Tektronix warrants that the products that it manufactures and sells, of the types listed below, will be free from defects in
materials and workmanship for a period of one (1) year from the date of shipment. If any such product proves defective during this warranty period, Tektronix, at its option, either will repair the defective product without charge for parts
and labor, or will provide a replacement in exchange for the defective product.
In order to obtain service under this warranty, Customer must notify Tektronix of the defect before the expiration of the
warranty period and make suitable arrangements for the performance of service. Customer shall be responsible for
packaging and shipping the defective product to the service center designated by Tektronix, with shipping charges
prepaid. Tektronix shall pay for the return of the product to Customer if the shipment is to a location within the country in
which the Tektronix service center is located. Customer shall be responsible for paying all shipping charges, duties,
taxes, and any other charges for products returned to any other locations.
This warranty shall not apply to any defect, failure or damage caused by improper use or improper or inadequate
maintenance and care. Tektronix shall not be obligated to furnish service under this warranty a) to repair damage
resulting from attempts by personnel other than Tektronix representatives to install, repair or service the product; b) to
repair damage resulting from improper use or connection to incompatible equipment; or c) to service a product that
has been modified or integrated with other products when the effect of such modification or integration increases the
ti me or difficulty of servicing the product.
THIS WARRANTY IS GIVEN BY TEKTRONIX WITH RESPECT TO THE LISTED PRODUCTS IN LIEU OF ANY OTHER
WARRANTIES, EXPRESS OR IMPLIED. TEKTRONIX AND ITS VENDORS DISCLAIM ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. TEKTRONIX' RESPONSIBILITY TO REPAIR OR
REPLACE DEFECTIVE PRODUCTS IS THE SOLE AND EXCLUSIVE REMEDY PROVIDED TO THE CUSTOMER FOR
BREACH OF THIS WARRANTY. TEKTRONIX AND ITS VENDORS WILL NOT BE LIABLE FOR ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES IRRESPECTIVE OF WHETHER TEKTRONIX OR THE VENDOR
HAS ADVANCE NOTICE OF THE POSSIBILITY OF SUCH DAMAGES.
TM 09361A-12
F7523A1 Mod WO
TABLE OF CONTENTS
Page
Page
Listof Illustrations ........................ iv
Listof Tables ............................ vi
Operators Safety Summary ................ vii
Section 1 System Overview
TestSet Description .................... 1.1.1
Major Components and Accessories ....... 1.1.2
System Specification
Table 1,1.1 Electrical
Characteristics.... ................ 1.1.3
Table 1.1.2 Environmental
Characteristics..................... 1.1.4
Physical Characteristics .............. 1.1.4
MeasurementBasics .... .............. 1.1.5
Measurement Fundamentals .......... 1.1.5
Filters in Audio Measurements ....... 1.1.5
1.1.6
Filters in Noise Measurements .......
Filters in Distortion Analysis .......... 1.1.6
Low-Pass Filters .................. 1.1.6
High-Pass and Notch Filters .......... 1.1.6
Distortion Measurements ............. 1.1,7
I M Distortion Measurements .......... 1.1.9
Monitoring....................... 1.110
Operating Instructions .................. 1.1.12
Twin-Tone Measurements ........... 1.1.12
Distortion Measurements ............ 1.1.12
Level Measurements ............... 1.1.14
Repackaging Information ............ 1.1.14
Storage Information ................ 1.1,14
Section 2 AA 501 A Mod WO Distortion Analyzer
Part1 Specification ........................ 2.1.1
Instrument Description ...............
Performance Conditions .............
Table 2.1.1 Electrical Characteristics .......
Table 2.1.2 Environmental
Characteristics.........................
Table 2.1.3 Physical Characteristics .......
2.1.1
2.1.1
2.1.2
2.1.7
2.1.8
Part 2 Operating Instructions ................. 2.2.1
Controls, Connectors, and
Indicators.........................2.2.1
Instrument Connections ..............2.2.3
2.2.4
LevelMeasurements ..............
Distortion Measurements ............ 2.2.5
2.2.7
Distortion Measurement Procedure ...
High Distortion Measurement
Limitations........................ 2.2.8
IM Distortion Measurements .......... 2.2.8
I M Distortion Measurement
Procedure...... ................. 2.2.10
. 2.2.10
Filters
Displays....................... . 2.2.11
Monitoring........................ 2.2.12
Section 3 SG 505 Mod WO Test Signal Oscillator
Part1 Specification ........................ 3.1.1
Introduction........................
Performance Conditions ............
3.1.1
31.1
Table 3.1.1 Electrical
Characteristics.................... 3.1 1
Table 3.1.2 Miscellaneous ............ 3.1.3
Table 3.1.3 Environmental
Characteristics.....................3.1.3
Table 3.1.4 Physical
Characteristics.....................3.1.4
Part 2 Operating Instructions ................. 3.2.1
Controls and Connectors ................
Operators Familiarization ...............
General Operating Information ........
Out utConnections ................
p
Fre uencySelection ................
q
Output Level Selection ...............
Rear Interface Signals ...............
3.2.1
3.2.3
3.2.3
3.2.3
3.2.3
3.2.3
3.2.3
TM 09361A-12
F7523A1 Mod WQ
TABLE OF CONTENTS (cont)
Page
Page
Part 1 Specification I.......... . ..
Introduction...........................
Performance Conditions ......... . .......
Table 4.1.1 Electrical Characteristics .......
Table 4.1.2 Miscellaneous ..............
Table 4.1.3 Environmental ................
a
g System ...... . .............. 5.2.3
FamilyCompatibility ...... . .......... 5.2.3
Installation and Pre Turn on
Procedure............................5.2.3
Buildin
Section 4 SG 505 Mod WR Oscillator
4.1.1
4,1.1
4.1.1
4.1.1
4,1,3
4.1.3
Part 2 Operating Instructions ................. 4.2.1
Controls and Connectors ................ 4.2.1
........ 4.2,3
Operators Familiarization .....
General Operating Information ........ 4.2.3
FrequencySelection ................ 4.2.3
Output Level Selection ............... 4.2.3
Twin-Tone Test Signal ...............4.2.3
OutputConnections ................. 4.2.3
Rear Interface Signals ............... 4.2.5
Section 5 TM 504A Mod WO Power Module
Part1 Specification ..... . .................. 5.1.1
Introduction........ . ................... 5,1.1
..
Descri tion
................ . . .. 5.1 1
p
Performance Conditions _ , 5.1 .1
Table 5.1.1 Electrical Characteristics . , ..... 5.1,1
Table 5.1.2 Physical Characteristics ....... 5.1.4
Part 2 Operating Instructions ................. 5.2.1
General.............................. 5.2.1
Installation......................... 5.2.1
PowerSource ...................... 5.2.1
PowerUsage ..................... 5.2.1
Line Voltage Selection/Fuse
Re lacement.. . ................... 5.2.1
p
Operating Temperatures ............. . 5.2.2
PowerModules .... ......... ..... 5.2.2
ModuleInstallation ............. . .... 5.2.2
Plug-In Module Retainer Bar
Installation......................... 5.2.3
Turn-on Procedure .................. 5.2.3
Section 6 Applications
Part1 Applications ......................... 6.1.1
Introduction...........................6.1.1
Basic Level Measurements ........... 6 1.1
Volta e.. , ....................... 6.1,2
g
dBm......................... 61.2
dBRatio ........................ 6 1.2
Harmonic Distortion (THD + N) ....... 6.1.2
Intermodulation Distortion ............ 6 1,3
SMPTEand DIN ................... 6.1.3
Twin-Tone ......................... 6.1.5
CCIF Difference Tone (IHF-IM) ........ 6.1.5
Make Common Audio
Measurements Easier ................ 6.1.6
Power..... . ...................... 6.1.6
Decibels.......................... 6.1.6
Gainand Loss ..................... 6.1.6
Fre uencyRes p onse ................ 6.1 .7
q
Signal-to-Noise Ratio (S/N) ......... 6.1.8
Harmonic Distortion Versus
Fre uency........ . . ............... 6.1.8
q
Distortion Versus Power or
Voltage...........................6.1.8
Distortion and Response Versus
Frequency at Constant Modulation
Percentage........................ 6.1.9
Determining Amplitude for
a Specific Distortion
Percentage....................... 6.1.11
SINAD...........................6.1.11
Intermodulation Distortion at
Nonstandard Frequencies ........... 6.1.12
Filters-internal and External ......... 6.1.12
Built-in Filters .................... 6.1.12
Modifying a 30-Hz Filter to the
22.4-kHz IEC Standard ............. 6.1.14
User-Supplied External Filters ........ 6.1.15
User-Built Filters .................. 6.1.15
TM 09361A-12
F7523A1 Mod WQ
TABLE OF CONTENTS (cont)
Page
Page
Spectrum Analyzer Driven from
AA 501A Mod WQ INPUT
MONITORConnector ............... 6.1 18
Section 6 Applications (cont)
Part 2 Applications (cont)
Using the INPUT MONITOR and
FUNCTION OUT Connections ........
Oscilloscope Monitoring ............
Spectrum Analyzers and
the AA 501 A Mod WQ ..............
Spectrum Analyzers and
the AA 501 A Mod WQ FUNCTION
OUTPUTConnector ................
Decibel-Converter Output ..........
6.1.15
6.1.16
6.1.16
6.1.16
6.118
Decibel Conversion Limitations p parentand Real ................. 6.1.20
A
DetectorOutput ................... 6.1.21
Twin-Tone High-Frequency-Tone
Output........................... 6.1.21
OperatorTraps .................... 6.1.21
TM 09361A-12
F7523A1 Mod WQ
LIST OF ILLUSTRATIONS
Page
Page
Section 3 SG 505 Mod WQ Test Signal Oscillator
Section 1 System Overview
1 .1.1
F7523A1 ModWQ ..................11.1
1.1.2
F7523A1 System Outline
Drawing.......................... 1.1.4
1.1.3
Typical device transfer
characteristics....................
1 1.7
1.1.4
Transfer characteristics of an
audiodevice .................... . . 1.1.8
1.1.5
Block diagram of a basic harmonic
1.1.8
distortion analyzer ..............
SMPTE, DIN or CCIF
1.1.9
IntermodTest ...............
IM test of transfer characteristics in
ti me and frequency domain .. ... .. 1.1,10
Block diagram of basic IM
analyzer......................... 1.1.11
Typical connections for distortion
measurements................... . 1.1.13
1.1.6
1.1.7
1.1.8
1.1.9
Section 2 AA 501 A Mod WO Distortion Anaiyzer
2.1.1
2.2.1
2.2.2
2.2.3
2.2.4
2.2.5
2.2.6
2.2.7
2.2.8
2.2.9
2.2.10
iv
AA501A Mod WQ Distortion
Analyzer...... .......... . ......... 2.1.0
Front panel controls and
connectors
.... . ......... . . .. 2.2.2
Typical connections for distortion
measurements..................... 2.2.4
Transfer characteristics of an
audiodevice ...................... 2.2.5
THD test of transfer
characteristics..................... 2.2.6
Block diagram of a basic harmonic
distortionanalyzer .................. 2.2.7
Block diagram of basic
IManalyzer ....................... 2.2.8
IM test of transfer characteristics in
ti me and frequency domain ........ 2.2.9
Response curves for
AA501A Mod WQ filters ......... , .. 2.2.11
Typical connections for distortion
measurements with monitoring ...... 2.2.12
Oscilloscope display of deviation
fromlinearity ..................... 2.2.13
3.1.1 The SG 505 Mod WQ Oscillator ....... 3.1.0
3.2.1 Front panel controls and
connectors........................ 3.2.2
Section 4 SG 505 Mod WR Output Oscillator
4.1.1
4.2,1
4.2.2
4.2.3
4.2.4
4.2.5
4.2.6
SG 505 Mod WR Oscillator .......... 4.1.0
SG 505 Mod WR front panel
controls and connectors .... . ........ 4.2.2
.. , ... _ 4,2.4
Connection configurations . ,
Floating oscillator ground to unit under
test to break up ground loops ....... 4.2.5
Added capacitor between CT and
chassis ground improves
RFI rejection.................. . . . . 4.2.6
SG 505 Mod WR CT terminal grounded
and cable shield connected to
ground post. Reduces RF
interference but may cause low
fre uency g round loop .............. 4.2.6
q
Three conductor shielded cable
allows CT to be remotely grounded
while cable shield is grounded at
bothends ........................ 4.2,7
Section 5 TM 504A Power Module
5.1.1 TM 504A Mod WQ Power
Module with Plug-Ins ...............5.1.0
5.1.2 TM 504A Mod WQ Outline
Drawing.......................... 5.1.3
5.2.1 Line voltage selection/fuse
replacement......................5.2.2
5.2.2 Keying assignments for family functions.
One of many possible sequence
combinations...................... 5.2.3
Section 6 Applications
6.1.1 Harmonic distortion added by device
under test is measured with
THDanalyzer ...................... 6.1.3
6.1.2 Typical noise limitation to THD + N
reading (with 80-kHz filter
selected) .........................6.1.4
TM 09361 A-12
F7523A1 Mod WO
LIST OF ILLUSTRATIONS (cont)
Page
6.1.3
6.1.4
6.1.5
6.1.6
6.1.7
6.1.8
6.1.9
6.1.10
6.1.11
Typical Residual THD + Noise
AA 501 A/SG 505 System (V input
> = 250 mV with 80-kHz-NoiseFiller
Limitin
) ..................... 6.1.4
g
SMPTE or DIN Intermod Test ......... 6.1.5
CCIF Intermod Test ................. 6.1.6
Voltage across load versus power
(Watts or dBW) .................... 6.1.7
Interconnection diagram for distortion
and response vs frequency
measurements....................6.1.9
Two variations of the "send"
e.....
...................6.1.10
p acka g
SINAD measurement setup ......... 6.1.12
Frequency response curve for
400 Hz high-pass filter ............. 6.1.13
Frequency response curve for
80 kHz low-pass filter .............. 6.1.13
Page
6.1.12 Frequency response curve for
30 kHz low-pass filter .............. 6.1.14
6.1.13 Frequency response curve for 'C' MSG
wei htedfilter .................... 6.1.14
g
6.1.14 Spectrum analyzer driven from
AA501A Mod WQ FUNCTION OUT
connector........................6.1.17
6.1.15 Spectrum analyzer display with
AA501 A Mod WQ and 7L5 distortion
device..........................6.1.18
6.1.16 Spectrum analyzer driven from
INPUT MONITOR connector ........ 6.1.19
6.1.17 Spectrum analyzer display showing
second and third order
products......................... 6.1.19
6.1.18 Audio-response sweeper package
using AA 501 A Mod WQ with FG 507
andSC 503 ..................... 6.1.20
V
TM 09361A-12
F7523A1 Mod WQ
LIST OF TABLES
Page
Page
3.1,3
3.1.4
Section 1 System Overview
1.1.1
Electrical Characteristics ............ 1.1.3
1.1.2
Environmental Characteristics ........ 1.1.4
Environmental .............. . ...... 3.1.3
Physical Characteristics ............. 3.1.4
Section 4 SG 505 Mod WR Output Oscillator
Section 2 AA 501 A Mod WQ Distortion Analyzer
............ 2.1.2
2.1.1
Electrical Characteristics
2.1.2
Environmental Characteristics ........ 2.1.7
2.1.3
Physical Characteristics ............. 2.1.8
2.2.1
Gains from INPUT terminals to
FUNCTION OUTPUT connector for
various settings of the INPUT
LEVEL RANGE control ............. 2.2.13
Section 3 SG 505 Mod WO Test Signal Oscillator
4.1,1
Electrical Characteristics ............ 4.1.1
4.1.2
Miscellaneous ..................... 4.1.3
4 .1.3
Environmental ..................... 4.1.3
Section 5 TM 504A Power Module
5.1.1
Electrical Characteristics
5.1.2
Physical Characteristics ............. 5.1.4
... 5.1 .1
Section 6 Applications
3.1.1
Electrical Characteristics
(Front Panel) ...................... 3.1. i
6.1.1 Variation of Common Mode Voltage with
In utLevel ........................ 6.1.1
p
3.1.2
Miscellaneous ..................... 3.1.x;
6.1.2 0 dB Reference Voltages ............ 6.1.7
vi
TM 09361A-12
F7523A1 Mod WQ
OPERATORS SAFETY SUMMARY
The general safety information in this part of the
summary is for both operating and servicing personnel.
Specific warnings and cautions will be found throughout
the manual where they apply, but may not appear in this
summary.
TERMS
Power Source
This product is intended to operate in a power module
connected to a power source that will not apply more
than 250 volts rms between the supply conductors or
between either supply conductor and ground. A protective ground connection by way of the grounding conductor in the power cord is essential for safe operation.
In This Manual
Grounding the Product
CAUTION statements identify conditions or practices
that could result in damage to the equipment or other
property.
This product is grounded through the grounding conductor of the power module power cord. To avoid electrical
shock, plug the power cord into a properly wired receptacle before connecting to the product input or output
terminals. A protective ground connection byway of the
grounding conductor in the power cord is essential for
safe operation.
WARNING statements identify conditions or practices
that could result in personal injury or loss of life.
As Marked on Equipment
CAUTION indicates a personal injury hazard not immediately accessible as one reads the marking, or a hazard
to property including the equipment itself.
DANGER indicates a personal injury hazard immediately
accessible as one reads the marking.
SYMBOLS
Danger Arising From Loss of Ground
Upon loss of the protective-ground connection, all
accessible conductive parts (including knobs and con.
trols that may appear to be insulating) can render an
electric shock.
Use The Proper Fuse
In This Manual
To avoid fire hazard, use only the fuse specified in the
parts list for your product, and which is identical in type,
voltage rating and current rating.
Q
Refer fuse replacement to qualified service personnel.
This symbol indicates where applicable
cautionary or other information is to
be found.
As Marked on Equipment
DANGER-High voltage.
Protective ground (earth) terminal
Q
ATTENTION - Refer to manual.
ORefer to manual.
Do Not Operate in Explosive Atmospheres
To avoid explosion, do not operate this product in an
explosive atmosphere unless it has been specifically
certified for such operation.
Do Not Operate Plug-In Unit Without Covers
To avoid personal injury, do not operate this product
without covers or panels installed. Do not apply power
to the plug-in via a plug-in extender.
vii
TM 09361A-12
Section 1
System Overview
TM 09361A-12
F7523A1 Mod WQ
TEST SET DESCRIPTION
F7523Al Mod WQ is a compact portable distortion test
set. The test set is comprised of a test set transmitter and
receiver. The test set transmitter provides a low distortion
signal source and an intermodulation disto rt ion 1:1 twintone signal source. The test set receiver provides a fully
automatic distortion analyzer
The test set transmitter is comprised of a SG 505 Mod
WQ Oscillator and a SG 505 Mod WR Oscillator coupled
together internally via the power module mainframe. The
test set receiver is comprised of the AA 501A Mod WQ
Distortion Analyzer. The test set transmitter and receiver
$6 SOS OSCILLATOR MOD WO
are installed in the TM 504A Mod WQ Power Module
mainframe. Refer to Fig. 1.1.1.
The test set transmitter generates custom twin-tone
frequencies from 2kHz to 100 kHz and single tone
frequencies of choice between 10 Hz and 100 kHz. The
twin-tone frequencies are generated by mixing the two
oscillators in a 1:1 ratio using the internal function or
externally in any desired ratio to produce the desired difference frequencies. The test set receiver provides
measurement functions for LEVEL (VOLTS, dBm, dB
RATIO), total harmonic distortion, SPMTE/DIN, and COIF
IMD. See Section 2, Part 2 for a discussion of these
measurement functions.
SGSMOSCIllATOA MOD
____
41
AASmIA DISTORTIONANALYZ9I MODWD
D
^
n
!
.
n
(
____
•
n
00
I:.:
C^
7813-01
Fig. 1.1.1. F7523A1 Mod WQ.
1.1.1
System Overview—F7523A1 Mod WQ
TM 09361 A-12
MAJOR COMPONENTS AND
ACCESSORIES
The F7523A1 Mod WQ includes the following:
Major Components
Quantity
Description
AA501 A Mod WQ Distortion Analyzer.
SG 505 Mod WQ Test Signal Oscillator
SG 505 Mod WA Test Signal Oscillator.
TM 504A Mod WQ Power Module.
Furnished Accessories
Quantity
Description
1
Cable Assembly, RE: 50 S-1 Coax, 20.0 L
(BNC to tip-jack cable) Tektronix Part Number 175-1178-00.
1
Power cord for TM 504A Mod WQ.
2
BNC female to dual banana adapters. Tektronix Part Number 103-0090-00.
Additional User- Supplied Items Needed for Operation and Use
Quantity
2
1.1.2
Description
Coaxial cables or twisted-wire pairs to connect system to device being tested.
TM 09361A-12
System Overview—F7523A1 Mod WQ
SYSTEM SPECIFICATION
(In addition to separate specifications for individual instruments)
Table 1.1.1
ELECTRICAL CHARACTERISTICS
Characteristics
Performance Requirements
Supplemental Information
TWIN-TONE MODE
Relative Amplitude Match
1:1 +0.5 dB
Thd of individual signals
0.1%
SYSTEM TOTAL HARMONIC DISTORTION
PLUS NOISE FUNCTION
Residual THD + N ( V1? 250 mV)
10 HZ —50 kHz, no filter
S 0.01 % rms Response (-80 dB)
50 kHz-100 kHz, no filter
50.10% rms Response (-60 dB) -- --
-
SYSTEM INTERMODULATION
Twin-Tone Residual IMD
POWER REQUIREMENTS
5-90 dB
Voltage Ranges
Selectable 100V, 110V, 120V
200V, 220V, and 240V nominal
li ne, ± 10%
Frequency Range
48 to 440 Hz
Power C onsumption
5 75 watts
1.1.3
TM 09361A-12
System Overview—F7523A1 Mod WQ
Table 1,1.2
ENVIRONMENTAL CHARACTERISTICS
Supplemental Information
Characteristics
Overall
Meets or exceeds MIL-T-28800D, Class 5 requirements.
Temperature
Operating
Non-operating
Humidity
0°C to + 50°C.
-55°C to +75°C.
90-95% RH for 5 days cycled to + 50°C.
Altitude
Operating
4.6 km (15,000 ft).
Non-operating
15 km (50,000 ft).
Vibration
0.38 mm (0.013"), 5 Hz to 55 Hz, 75 minutes.
Shock
40 g's (terminal sawtooth), 11 ms, 18 shocks.
Bench handling
45 °, 4", or equilibrium, whichever occurs first.
Transportation
Qualified under National Safe Transit Association Preshipment Test
Procedures 1 A-B-1 and 1A-B-2.
PHYSICAL CHARACTERISTICS
11.125
18.625
I
5.375
i
781
Fig 1.1.2. F7523A1 System Outline Drawing.
1.1.4
TM 09361A-12
System Overview—F7523A1 Mod WO
MEASUREMENT BASICS
Measurement Fundamentals
Much of the special vocabulary used by audio and communications workers relates to the dB (decibel). Since
level measurements are common from several tens of
volts on down to microvolts, the industry long ago standardized on using dB to express both absolute levels
and ratios of signals.
In the broadcasting, recording, and satellite/microwave/
telephone industries, absolute levels are also referred to
in dB rather than volts or watts. The most common reference is one milliwatt. Levels referred to one milliwatt are
expressed in dBm. Watts are clearly a power unit, but
most level-measuring instruments are voltmeters (not
wattmeters) and are not sensitive to circuit impedance.
They must be calibrated for some particular value of
i mpedance if they are to display dBm (power) even
though they really measure voltage; 600 ohms is the
most common circuit impedance in broadcasting and
recording (150 ohms is also frequently used). Most of the
other special terminology is in the area of standard
industry specifications. SMPTE is the Society of Motion
Picture and Television Engineers. DIN is the Deutsches
Institut fur Normalung, German standards. CCIR, CCIF,
and CCITT are all French initials for International Radio
Consultative Committee, International Telephone
Consultative Committee, and international Telegragh
Consultative Committee, all European standards. IEC is
the International Electrotecflnical Commission. IHF is
the Institute of High Fidelity Manufacturers and EIA is the
Electronic Industries Association. SINAD stands for the
ratio of (signal + noise + distortion) to (noise +
distortion).
Most measurements in the audio and communication
world are made below 100 kHz and fall into two broad
categories: level and non-linearity. Level measurements include frequency response, gain/loss, noise
level or signal-to-noise (S/N) ratio, power, and crosstalk/separation/isolation. Nonlinearity measurements
include total harmonic distortion (THD), THD plus noise
(THD + N), individual harmonic distortion, intermodulation distortion (IMD; standards include SMPTE,
DIN, CCIF, and Twin-Tone).
Communications and audio equipment under ideal conditions faithfully reproduces an input signal at its output.
When this signal is not faithfully reproduced, it is said to
be distorted. Nonlinearity in system circuits causes
harmonic and intermodulation distortion to be present.
This distortion consists of frequency components
present in the output signal that are not contained in the
input signal. This will appear to the user as poor sound
quality, noise or channel cross-talk. Harmonic distortion
is the result of undesired harmonic related frequencies
being generated from a pure tone stimulus (input signal).
Intermodulation distortion is the result of undesired intermodulation being generated from a pure two tone stimulus. Harmonic distortion and intermodulation distortion
are merely two different techniques to measure the
results of nonlinearities. Which technique is most appropriate depends upon several factors, most importantly
on whether the device being tested is wideband or has a
sharp upper frequency cutoff.
Harmonic distortion tests are the most common test for
amplifiers. A 1 kHz signal is the standard test tone.
Harmonics can then be predicted for the 2nd harmonic at
2 kHz, 3rd harmonic at 3 kHz, etc. Therefore, harmonic
distortion test aren't very useful above a frequency equal
to one-third to one-half the upper band of the device
under test (DUT). SMPTE/DIN is a better test for HIFidelity devices; while the CCIF method is more appropriate for sharp upper frequency cutoff as in voice grade
communications links or recorders.
The total of these frequency components present in the
signal, in addition to the fundamental frequency, can be
measured quickly with a distortion analyzer. A distortion
analyzer with the use of appropriate filters, tunes out the
fundamental frequency and measures the amplitude of
the remaining frequency components. Refer to Section 6
for an Application Note on Common Audio Frequency
Measurements.
Most audio measurements are stimulus/response
measurements; that is, a suitable stimulus is applied to
the input of the device- under-test and the measurement
is then made at the output. The F7523A1 Mod WQ
distortion test set provides this capability.
Filters in Audio Measurements
Distortion analyzers, audio voltmeters, and other audio
test equipment often have built-in, selectable filters.
How to use them, what to expect from them, and what to
avoid are complex issues. The majorfiltertypes in distortion analyzers are filters for noise measurements, filters
for distortion analysis, low-pass filters, high-pass
filters, and notch filters.
1.1.5
TM 09361 A-12
System Overview- F7523A1 Mod WO
Filters in Noise Measurements
For an audio-frequency unit or system, the goal of noise
measurements is quantifying the noise level or the ratio
of the normal signal level to the noise level. The
measurement equipment is either a wideband audio
voltmeter or a distortion analyzer's LEVEL section. For
noise measurements in audio systems that people listen
to, components beyond 20 kHz are probably irrelevant.
Human hearing sensitivity is not constant from 20 Hz to
20 kHz. For a given loudness, midband frequencies
require less power than low or high frequencies.
Because of this varying response, a flat-response voltmeter noise measurement doesn't correlate well with the
noise that people hear.
To improve the correlation, weighting filters have been
developed. Their response curves approximate the
inverse of the ear's sensitivity curves. In the United
States, "A" weighting is used more than other noise-weighting curves.The 'C' MSG filter is another standard
that is often used in communications.
Filters in Distortion Analysis
Distortion analyzers measure the affects of all harmonics
plus noise by first using a notch-filter to remove the fundamental frequency of a test tone and then measuring
the RMS (or the average) sum of the remaining signals.
The remaining signals may include these elements:
• Harmonics of test tone generated by nonlinearities
in the test devices.
• Broadband noise.
• Interfering signals such as a stereo pilot tone in an
FM stereo system.
Low-Pass Filters
Todays better audio equipment typically has low levels
of distortion. Accurate measurement of the actual harmonic distortion may be restricted by the broadband
noise of the device under test and by the distortion
analyzer itself.
Distortion analyzers often include low-pass (bandli miting) filters to reduce the noise seen by the detector.
This reduction permits harmonic measurements at even
1.1.6
lower amplitudes. Typically, these filters are an 80 kHz
low-pass filter and a 30 kHz low-pass filter.
None of these filters attenuate any of the standard 1 kHz
test signal's important harmonics. However, selecting
the 30 kHz low-pass filter would be inappropriate for
THD measurements at any fundamental frequency
above 15 kHz, because all harmonics would be
attenuated. Even with a 10 kHz fundamental, the 30 kHz
low-pass filter significantly attenuates (3 dB) the third
harmonic.
The combination of the fundamental frequency and
selected filter should not attenuate the second or third
harmonics, and perhaps not the fourth and fifth
harmonics. If 3 dB attenuation of the fifth harmonic is the
criterion, 6 kHz is the highest test oscillator frequency
appropriate for 30 kHz low-pass filter use. The 80 kHz
low-pass filter could be used with oscillator frequencies
up to 18 kHz.
High-Pass and Notch Filters
Broadband noise is the most common distortion
measurement limitation. Hum introduced in a test unit by
a poorly filtered power supply or by poor shielding
may also set a floor under harmonic distortion
measurements. Using fillers within the audio band can
produce more impressive measurements. They an also
obscure problems in the tested equipment.
Most distortion analyzers contains a 400 Hz high-pass
filter which can be used to reduce the effects of hum in
measurements of total harmonic distortion with 1 kHz or
higher fundamentals. Because the filter would attenuate
the tone itself, it cannot be used with fundamentals
below 1 kHz.
Using a filter in the test equipment to reject the effects of
audible hum may not be appropriate. Unless the audio
system uses loudspeakers that reject most of the hum at
the power-mains frequencies, the hum will be audible
even though it was eliminated from distortion measurements by use of a filter in the analyzer.
Distortion measurements in stereo FM transmitters,
tuners, and receivers are a special case. Commonly
used systems have a 19 kHz pilot tone. Because most
adults can't hear this frequency, most tuners provide little
rejection of it, However, the distortion analyzer can
"hear" the 19 kHz pilot tone. A high level 19 kHz pilot tone
may prevent the distortion analyzer from measuring
significant harmonics of a 1 kHz test tone. An external
19 kHz notch filter solves the problem.
TM 09361A-12
System Overview—F7523A1 Mod WQ
Distortion Measurements
Distortion is a measure of signal impurity. It is usually
expressed as a percentage of dB ratio of the undesired
components to the desired components. Harmonic
distortion is simply the presence of harmonically related
or integral multiples of a single pure tone called the
fundamental, and can be expressed for each particular
harmonic. Total harmonic distortion, or THD, expresses
the ratio of the total power in all significant harmonics to
that in the fundamental.
The transfer (input vs output) characteristics of a typical
device is shown in Fig. 1.1.3. Ideally this is a straight line.
A change in the input produces a proportional change in
the output. Since the actual transfer characteristic is nonli near, a distorted version of the input waveshape
appears at the output. The output waveform is the
projection of the input sine wave on the device transfer
characteristic as shown in Fig. 1.1.4. The output
waveform is no longer sinusoidal, due to the nonlinearity
of the transfer characteristic, Using Fourier analysis it
can be shown that the output waveform consists of the
original input sine wave, plus sine waves at integer multiples of the input frequency. These harmonics represent
nonlinearity in the device under test. Their amplitudes
are related to the degree of nonlinearity.
A total harmonic distortion measurement inevitably
includes effects from noise to hum. The term THD + N
has been recommended ) to distinguish distortion
measurements made with a distortion analyzer from
those made with a spectrum analyzer.
IHF-A-202 1978, Standard Methods of Measurement for
Audio Amplifiers, The Institute of High Fidelity, Inc., 489 Fifth
Avenue, New York, N.Y. 10017
Fig. 1.1.3. Typical device transfer characteristics.
1.1.7
TM 09361A-12
System Overview—F7523A1 Mod W®
and then performing a root-mean-square summation of
the harmonics to produce a THD number uninfluenced
by broadband noise and other components such as ac
hum or interference. However, it is relatively complex,
ti me consuming, and requires interpretation of a graphic
display.
An appealing feature of the THD + N (total harmonic distortion plus noise) measuring technique is that the meter
presents one number integrating harmonics, broadband
white noise, hum, and specific interfering signals.
Distortion analyzers can quantify the nonlinearity of a
device or system. A distortion analyzer removes the fundamental of the signal investigated and measures the
remainder. See Fig. 1.1.5. Because of the notch filter
response, any signal other than the fundamental
influences the measurement.
Fig. 1.1.4. Transfer characteristics of an audio device.
A spectrum analyzer allows direct measurement of each
harmonic. The spectrum analyzer technique involves
making a narrow-band measurement of each harmonic,
Many audio devices and systems contain internal filters
that the user cannot control. Digital audio tape and compact disc players have sharp cut-off filters slightly above
20 kHz. Many telephone voice channels and two-way
radio transmitters cut off around 3 kHz. AM radio transmitters may roll off between 5 kHz and 10 kHz. Stereo FM
transmitters must roll off below 19 kHz.
A I FUNDAMENTAL AFUNDAMENTAL A
FUNDAMENTAL
ELIMINATED
1 ,
1
F
OSCILLATOR
liii
F
/
F
DEVICE
/J CONVERTER
AC TO DC
UNDER
TEST HTFILTER
F
READOUT
7813-05
Fig. 1.1.5. Block diagram of a basic harmonic distortion analyzer.
1.1.8
TM 09361A-12
System Overview—F7523A1 Mod WO
As shown in Fig. 1.1.7, when this composite signal is
applied to the device, the output waveform is distorted.
As the high frequency tone is moved along the transfer
characteristic by the low frequency tone, its amplitude
changes. This results in low frequency amplitude modulation of the high frequency tone. This modulation is
apparent in the frequency domain as sidebands around
the high frequency tone. The power in these sidebands
represents nonlinearity in the device under test.
Given those conditions, THD measurements are meaningless between 10 kHz and 20 kHz in a digital audio
system that has a 20 kHz internal filter. Also, no third
harmonic information can be obtained with fundamentals above 6.7 kHz. The only way to determine a
band-limited system's linearity in the top one or two
octaves is with intermodulation testing.
I M Distortion Measurements
The output signal is high-pass filtered to remove the low
frequency component. The high frequency tone is then
demodulated, as an AM radio signal. The demodulator
output is low-pass filtered to remove the residual carrier
(high frequency) components. The amplitude of the low
frequency modulation is displayed as a percentage of
the high frequency level. See Fig, 1.1.8.
Another measurement of distortion investigates the interaction of two or more signals, Nonlinearities in the
device under test cause the sine waves to cross modulate. The amplitude ratio of low to high frequencies
should be between 4:1 and 1:1. Many tests have been
devised to measure this interaction. Four common standards are SMPTE, DIN, CCIF and Twin-Tone.
The SMPTE standard test frequencies are 60 Hz and
7 kHz. The DIN standard is virtually identical to the
SMPTE standard except for the two frequencies used.
They may be any pair of octave band center frequencies,
with the upper at least eight times as high as the lower
(250 Hz and 8 kHz are most common).
To measure intermodulation distortion (IMD), according
to SMPTE, DIN or CCIF standards, the device under test
is excited with a low frequency and high frequency signal
simultaneously (Fig. 1.1.6).
INTERMOD
PRODUCTS
LF
(60 Hz SMPTE)
(250 Hz DIN)
LOW FREQUENCY
OSCILLATOR
+
DEVICE
HF I
(7 kHz SMPTE)
(8 kHz DIN)
ANALYZER
14 kHz 15 kHz
HIGH FREQUENCY
OSCILLATOR
1 kHz
DIFFERENCE
TONE
HF
TONES
( CCIF)
781
Fig. 1.1.6. SMPTE, DIN or CCIF Intermod Test.
1.1.9
TM 09361A-12
System Overview—F7523A1 Mod WQ
TRANSFER (INPUTCHARACTERISTI
TEST DEVIC
PUT
RTED)
7813
-071
Fig. 1.1.7. IM test of transfer characteristics in time and frequency domain.
To measure twin-tone difference frequency distortion,
the device is excited with two input signals as described
above. The output of the device is low-pass filtered to
remove the two test tones and extract the difference
frequency product. The level of this component is
expressed as a percentage of the high frequency signals. The AA 501 A CCIF difference frequency mode will
accept any pair of input frequencies which are within
li mits as listed in the Specification section. The amplitudes of the two signals should be equal.
The AA 501 A Mod WQ is capable of measuring THD + N
and automatically selecting and performing all three IMD
tests. The AA 501 A Mod WQ can accept a wide of test
frequencies and any pair of test frequencies which are
within the limits as listed in the Specification section.
1.1.10
Monitoring
The AA 501 A Mod WQ has facilities for monitoring of the
input signal and the distortion components after removal
of the fundamental frequency.
The input signal may be monitored on an oscilloscope
for evidence of clipping. Monitoring the input signal with
a spectrum analyzer during twin-tone measurements
provides information on the harmonics other than the
difference frequency.
The monitoring of the distortion components with an
oscilloscope can help determine their composition.
Triggering the oscilloscope on the same line frequency
as the DUT will result in a stable display of the line
frequency related components. Monitoring of the
frequency components with a spectrum analyzer will
provide information on harmonic amplitudes.
TM 09361A-12
System Overview—F7523A1 Mod WQ
A
A
A
A
F
F
F
F
LOW FREQUENCY
OSCILLATOR
^{-
HIGH
PASS
DEVICE
LOW
PASS
DEMODULATOR
AC/DC
FILTER
FILTER
METER
HIGH FREQUENCY
OSCILLATOR
!^^,i. ,i
IIIIIIIII
11
11
1
1
1
Illi
„
II
II
^
I I , ' II
I
I I
I
III
II,,
I
I ^
il+l
III. _.
I.
^
III
I
III --__
I
Il
l ll
li
IIIIII ,
I
I
I
I
III'.
I,I'„
II
'
I
,I^i^
111111,
^
I
II
iI^IVI
7813- 8
0
Fig. 1.1.8. Block diagram of basic IM analyzer.
1.1.11
TM 09361A-12
System Overview— F7523A1 Mod WQ
OPERATING INSTRUCTIONS
F7523A1 Mod WQ is easily operated. Both oscillators in
the transmitter section have a frequency range of 10 Hz
to 100 kHz. Each oscillator may be used independently
or together to produce an IMD test signal. The distortion
analyzer of the receiver section may be used as an ac
voltmeter, dBm level meter, dB ratio meter, or distortion
analyzer.
Fundamental frequency oscillator, SG 505 Mod WR, has
a dual female banana output connector. The modulating
frequency oscillator is internally connected to the fundamental oscillator. The OUTPUT ON/OFF push button on
the modulating oscillator disconnects the signal from its
output connector. The two tone test signal 1:1 push
button on the fundamental oscillator must be pushed in
for two tone testing. See Fig. 1 1.9 for a typical configuration for distortion testing.
The complete operating instructions for each instrument
comprising the F7523A1 Mod WQ is provided in its
respective section of this manual. The operator should
review these sections before proceeding.
Twin-Tone Measurements
Twin-Tone testing is done to measure the effect of
device nonlinearity. Two equal-amplitude, closely
spaced signals are fed to the device under test. If asymmetric nonlinearities exist, a second order difference
product will be produced at the low frequency signal
equal to their spacing. To make this measurement
requires a low-pass filter followed by a voltmeter, as
provided by the AA 501 A Mod WQ.
Two SG 505 Oscillators are required to generate the test
signal. The two oscillators are combined internally and
their amplitudes are set for a 1:1 ratio. The AA 501 A Mod
WQ will automatically measure the amplitude of the difference tone.
Twin-Tone measurements are made by adjusting the
output of the test set transmitter to the recommended test
level on the test set receiver. After the required reference
is set, the test set transmitter is connected to the device
under test (DUT). The output of the DUT is connected to
the test set receiver and the distortion measured
To adjust the output of the test set transmitter, connect
the output of the fundamental oscillator, SG 505 Mod
WR, to the test set receiver, AA 501 A Mod WQ. Select the
test frequencies on both the fundamental and
1.1.12
modulating oscillators. Activate the 1:1 two tone push
button on the fundamental oscillator. Select the LEVEL
FUNCTION mode of the test set receiver and the appropriate Input Level Range on AUTO RANGE. Push the
OUTPUT ON/OFF push button on the fundamental oscillatorto the ON position. Adjust the OUTPUT LEVEL of the
fundamental oscillator to obtain the required signal level
on the test set receiver.
CAUTION
If the GNDED/FLTG switch on either of the oscillators in the transmitter is set to GNDED, the
OUTPUT connector outer conductor (shield)
will be connected to chassis ground through a
low impedance
Disconnect the fundamental oscillator from the test set
receiver and connect to the DUT The output of the DUT is
connected to the test set receiver. The receiver has
several filters available which may be selected for the
measurement. With the test set receiver in the LEVEL
FUNCTION mode, adjust the INPUT RANGE control until
the DECREASE RANGE and INCREASE RANGE lights
extinguish or select AUTO RANGE FUNCTION. Select
the appropriate percent of distortion range and type of
distortion measurement; THD + N for harmonic distortion plus noise measurements or IMD for SMPTE/DIN,
CCIF, and Twin-Tone measurements. The percent of distortion is now indicated on the test set receiver.
For two tone testing when other than a 1:1 ratio is
required, connect the two oscillators outputs together
externally. Adjust the oscillators' frequency and output
level to the required levels and proceed as described
above.
For totally automatic distortion measurements, select
the desired filter, type of distortion measurement and
then select the AUTO RANGE FUNCTION. The percent of
distortion will automatically be displayed.
Distortion Measurements
The total harmonic distortion plus noise (THD + N)
method of testing a DUT involves using a single pure
tone stimulus. Nonlinearities in the DUT will produce
harmonics. The relative strength of the harmonics plus
noise is an indicator of DUT linearity.
TM 09361A-12
System Overview—F7523A1 Mod WQ
$G5
UM60SCIUATORMWWO
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COAXIAL
CABLE
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SHIELDED TWISTED PAIR
FOR MAXIMUM HUM
REDUCTION
DUT
INPUT GROUND
OUTPUT
LOAD
7813-09
Fig. 1.1.9. Typical connections for distortion measurements.
THD + N measurements with the F7523A1 Mod WQ are
easy. The controls have been automated and provide the
operator with the flexibility of choosing auto or manual
modes of operation.
To make a THD + N measurement, set the test oscillator
(one of the SG 505) to the desired test frequency and output level. The AA 501A Mod WQ LEVEL FUNCTION may
be used to establish the output level.
Connect the test oscillator to the DUT input. Connect the
output DUT to the AA 501 A Mod WQ input with a shielded
cable. In manual operation, adjust the INPUT RANGE
control until the range LEDs are extinguished. Select
THD + N and the highest distortion range (20%), then
adjust the distortion range to the range that provides an
onscale reading. For auto operation, select THD + N
and AUTO RANGE for INPUT RANGE and distortion. The
RMS position of the RESPONSE button should be used.
1.1.13
TM 09361A-12
System Overview—F7523A1 Mod WQ
Level Measurements
Level measurements can easily be accomplished using
the AA 501 A Mod WQ. Select the LEVEL function and the
desired readout units button; VOLTS, dBm 600 OHMS, or
dB RATIO Set the INPUT RANGE to AUTO RANGE for
auto operation or adjust the range manually.
When measuring signal to noise ratio or making noise
level measurement, it is often desirable to employ a
frequency dependent weighting network. For most
noise-level measurements use the 'C' MSG weighting
filter: select LEVEL mode, VOLTS, or dBm, and read the
display.
For signal-to-noise measurements, do not have the
weighting filter selected when you set up the signal
(tone) reference level to which noise will be compared.
Unless the reference frequency is exactly at the
weighting filter response curve's 0.0 dB gain point, the
filter causes errors in the reference-tone level setup So,
disengage the filter, establish the reference tone
frequency with the test oscillator, and adjust the
oscillator for the specified level.
• Select dB RATIO and press the PUSH TO SET 0 dB
REF button.
• Remove the test oscillator and back terminate
(replace the oscillator with a resistor equal to the
oscillator output characteristic impedance). With the
Tektronix SG 505 Oscillator, you can do this step
simply by pressing the OFF button.
the owner (with address) and the name of an individual at
your location that can be contacted. Include the complete instrument serial number and a description of the
service required.
Save and reuse the package in which your instrument
was shipped. If the original packaging is unfit for use or
not available, repackage the instrument as follows:
Surround the instrument with polyethylene sheeting to
protect the finish of the instrument. Obtain a carton of
corrugated cardboard of the correct carton strength and
having inside dimensions of no less than six inches more
than the instrument dimensions. Cushion the instrument
by tightly packing three inches of dunnage or urethane
foam between carton and instrument on all sides. Seal
the carton with shipping tape or an industrial stapler.
The carton test strength for this instrument is 200 pounds
per square inch.
Storage Information
1.
After repackaging store in a clean, dry, environment.
2.
In a high humidity environment protect the system
from temperature variations that could cause internal condensation.
3.
Outdoor storage is not recommended.
4.
Environment: Store within the following environmental limits.
• Engage the weighting filter and read the weighted
signal-to-noise ratio.
Temperature
Altitude
Relative Humidity
Repackaging Information
If the Tektronix instrument is to be shipped to a Tektronix
Service Center for service or repair, attach a tag showing
1.1.14
5.
-40 to 71 °C
_< 4570 m (15,000 feet)
95% @ 30° to 60 °C
No ventilation or preservation required.
TM 09361A-12
Section 2
AA 501A Mod WQ
Distortion Analyzer
F7523A1 Mod WQ—AA 501A Mod WO
Figure 2.1.1. AA501A Mod WQ Distortion Analyzer.
2.1.0
TM 09361A-12
TM 09361A-12
Part 1 —F7523A1 Mod WQ—AA 501A Mod WQ
SPECIFICATION
Instrument Description
The AA 501A Mod WQ is a fully automatic distortion
analyzer packaged as a two-wide TM 500 plug-in. Total
harmonic distortion can be measured with the AA 501A
Mod WQ as well as SMPTE/DIN intermodulation
distortion and CCIF two-tone difference frequency
distortion.
Distortion set level, frequency tuning and nulling are fully
automatic, requiring no operator adjustment. Input level
range and distortion measurement range selections are
fully automatic or may be manually selected. Distortion
readout is provided in percent or dB.
The AA 501A Mod WQ is also a high sensitivity,
autoranging, audio frequency voltmeter. Readings may
be in volts, dBm, or dB relative to any arbitrary reference.
Filters are included which allow measurement of noise to
IHF and FCC specifications. A hum rejection filter is provided as are provisions for external filters.
All readings are displayed on a 3 1/2 digit readout An
uncalibrated analog readout is also provided to aid in
nulling and peaking applications.
Ac to dc conversion is either average or true rms
responding, allowing conformance with most standards.
Ac input and output connections are available on both
the front panel and the rear interface. Dc signals,
corresponding to the displayed reading, are available
through the rear interface. This allows flexibility in interconnection with other instruments such as filters, chart
recorders, spectrum analyzers, oscilloscopes, etc.
Performance Conditions
The electrical characteristics in this specification are
valid only if the AA 501 A Mod WQ has been adjusted at
an ambient temperature between + 20 degrees C and
+30 degrees C. The instrument must be in a noncondensing environment whose limits are described
under the environment section. Allow twenty minutes
warm-up time for operation to specified accuracy; sixty
minutes after exposure to or storage in a high humidity
(condensing) environment. Any conditions that are
unique to a particular characteristic are expressly stated
as part of that characteristic.
The electrical and environmental performance limits,
together with their related validation procedures,
comprise a complete statement of the electrical and
environmental performance of a calibrated instrument.
Items listed in the Performance Requirements column of
the Electrical Characteristics are verified by completing
the Performance Check in the Calibration section of this
manual. Items listed in the Supplemental Information
column are not verified in this manual.
2.1.1
TM 09361A-12
Specification—F7523A1 Mod WG—AA 501A Mod WG
Table 2.1.1
ELECTRICAL CHARACTERISTICS
Characteristics
Performance Requirements
Supplemental Information
INPUT (all functions)
I mpedance
100 kf ±2%, each side to ground.
Full differential. Each side ac
coupled through 1 µF and shunted
to ground by approximately 200 pF.
Dual banana jack connectors at
0.750 inch spacing with ground connector additionally provided.
Input ranges
200 µV to 200 V in 10 steps.
2-6 sequence from 200 µV to 200 V
Range selection is manual or automatic. Autoranging time is typically
<1 second. Separate increase
range and decrease range indicators illuminate whenever input
level does not fall within optimum
window for selected range. For
specified instrument performance
both indicators must be
extinguished.
300 V peak, 200 V rms either input
to ground or differentially. Will recover without damage from overloads of 120 V rms continuously or
200 V rms for 30 minutes on all
ranges. For linear response, peak
input voltage must not exceed 3
ti mes INPUT LEVEL RANGE setting.
Maximum input voltage
Common mode rejection
(inputs shorted)
^ 50 dB at 50 or 60 Hz for common
mode signals up to one-half of selected
input range or 50 mV, whichever is
greater.
Typically ? 40 dB to 300 kHz.
LEVEL FUNCTION
Modes
Accuracy V;,, in 2100 µV
(-78 dBm) with level ranging indicators extinguished.
(T<_ +40°C)
20 Hz to 20 kHz
Volts, dBm (600 fl), or dB ratio with
push to set 0 dB reference. Input
range determines display range.
Single effective range in dB modes
with 0.1 dB resolution. Stored 0 dB
reference is unaffected by subsequent changes in mode or function.
VOLTS.
dBm OR dB
RATIO.
Within ±(2%+1
± 0.3 dB.
count).
10 Hz to 20 Hz and 20
Within ±,(4% +2
count).
2.1.2
±0.5 dB.
TM 09361A-12
Specification—F7523A1 Mod WO—AA 501A Mod WO
Table 2.1.1 (cont)
Characteristics
Performance Requirements
Supplemental Information
LEVEL FUNCTION (cont)
Bandwidth
(no filters selected)
At least 300 kHz.
Residual noise (Inputs
shorted, T 5 +40°C)
<3.0 µV (-108 dBm) with 80 kHz,
400 Hz filters.
TOTAL HARMONIC
DISTORTION PLUS NOISE
FUNCTIONS
Fundamental frequency
range
10 Hz to 100 kHz.
Fully automatic tuning and nulling.
For proper tuning THD + N X10%
After initial tuning THD + N can
degrade to 30% without loss of lock
for SINAD testing. Typical nulling
ti me is less than 5 s above 20 Hz.
Distortion ranges
Auto range, 20 %, 2%, 0.2%, and
dB. dB is internally autoranging with
single effective display range. Auto
range allows measurements above
20%.
Accuracy (THD 5 30% and
reading _>4% of selected
distortion range).
Accuracy is limited by residual
THD+N and filter selection. 100%
reference level is total input signal
amplitude including distortion and
noise components.
20 Hz to 20 kHz
Wits in ± 10% (± 1 dB) for harmonics
=100 kHz.
10 Hz to 100 kHz
Within + 10% -20% (+ 1 dB, -2 dB) for
harmonics < 300 kHz..
Residual THD+N (Va,
2 250 mV, all distortion,
noise, and nulling error
sources combined,
T540°C)
Measured with SG 505 oscillator..
10 Hz to 50 kHz,
no filter
_< 0.0071 % rms Response (-83 dB).
50 kHz to 100 kHz,
no filter
<0.010% rms Response (-80 dB).
Typical fundamental
rejection
At least 10 dB below specified
residual THD + N or the actual
signal THD, whichever is greater.
2.1.3
TM 09361A-12
Specification—F7523A1 Mod WO—AA 501A Mod WO
Table 2.1.1 (cont)
Characteristics
Performance Requirements
Supplemental Information
INTERMODULATION
DISTORTION FUNCTION
Fully automatic SMPTE, DIN, or
CCIF difference tone tests
depending upon actual input signal
whenever respective IMD <_ 20%.
Distortion ranges are same as
THD + N function. Internal jumper
selects Automatic, CCIF, or
SMPTE/DIN,
Operation
SMPTE/DIN tests
Lower frequency range
50 Hz to 250 Hz.
Upper frequency range
Usable from 2 kHz to 160 kHz.
Level ratio range
1:1 to 4:1, Iower:upper.
Residual IMD V;,,
250 mV, 60 Hz, and
8 kHz, 4:1 amplitude
ratio, T < +40°C
Measured with SG 505 pair.
< -90 dB.
CCIF difference tone test
Usable from 2 kHz to 160 kHz.
Frequency range
40 Hz to 1 kHz.
Difference frequency range
Minimum input level
60 mV(--22 dBm).
Residual IMD V 1
250 mV,
2 kHz and 2.5 kHz,
T <+40°C
_ -90 dB.
Measured with SG 505 pair.<
Accuracy (IMD 5 20% and
reading '?4% of selected
distortion range)
Within ± 10% (± 1 dB) for IM components <1 kHz (Accuracy is limited by
residual IMD and filter selection.)
FILTERS
400 Hz high pass
-3 dB at 400 Hz ± 5%; at least -40 dB
rejection at 60 Hz.
Three pole Butterworth response.
80 kHz low pass
-3 dB at 80 kHz ±5%.
Three pole Butterworth response.
30 kHz low pass
-3 dB at 30 kHz ±5%.
Three pole Butterworth response.
"C" message weighting
External filter
2.1.4
Within recommendation of IEEE
standard '743-1984.
Selects front panel AUXILIARY INPUT
allowing connection of external filter
between it and FUNCTION OUTPUT.
TM 09361A-12
Specification—F7523A1 Mod WO—AA 501A Mod WQ
Table 2.1.1 (cont)
Characteristics
Performance Requirements
Supplemental Information
FRONT PANEL SIGNALS
Input Monitor
V; r , ? 50 mV
1 V rms ± 10% (10 Hz to 100 kHz).
Constant amplitude (average response) version of differential input
signal. THD is typically<- 0.0010%
(-100 dB) from 20 Hz to 20 kHz.
Setting time is 51.5 seconds.
Approximately 20 times input signal.
V, 5 50 mV
Function Output
Signal
1 V, ±3%, for 1000 count volts or %
display.
I mpedance
1 kf2, ±5%.
Selected and filtered ac signal
actually measured.
Auxiliary Input
Sensitivity
1 V, ±3%, for 1000 count volts or %
display.
15 V peak, 6 V peak for linear
response.
Maximum Input Voltage
I mpedance
Loop through accuracy from
FUNCTION OUTPUT is ±3%.
100 kfl, ±5%.
Ac coupled.
REAR INTERFACE
Rear interface input
Pins 28B(+), 28A(-), 27B and 27A
(common) are front panel selectable
and independent of main front panel
input. All characteristics are the
same as main INPUT except maximum input voltage is limited to 42 V
peak, 30 V rms. Due to potential
crosstalk at the rear interface, noise
and distortion performance may be
degraded.
Input monitor
Pins 24A and 23A (gnd) same as
front panel INPUT MONITOR.
Function output
Pins 23B and 24B (gnd) same as
front panel FUNCTION OUTPUT.
Auxiliary input
Pins 25B and 26B (gnd) same as
front panel AUXILIARY INPUT Maximum input voltage is 15 V peak, 6 V
peak for linear operation.
Ac/dc converter output
Pins 20A and 19A (gnd). Dc output
of the selected ac to dc converter.
1 V ±5% for 1000 count display
with 500 (1 ± 5% source resistance.
2.1.5
TM 09361A-12
Specification—F7523A1 Mod WO—AA 501A Mod WO
Table 2.1.1 (cont)
Performance Requirements
Characteristics
Supplemental Information
REAR INTERFACE (cont)
Pins 19B and 20B (gnd). Dc output
of the logarithmic dB converter.
10 mV ±5% equals 1 dB of display
with 1 kf ±5% source resistance..
Changes in level or distortion range
will cause brief ac transients.
dB converter output
DETECTORS AND DISPLAYS
Detectors (Response)
RMS
True rms detection.
AVG
Average detection, rms calibrated
for sinewaves. Typically reads 1 to
2 dB lower than true rms detection
for noise, THD+N, and IMD
measurements.
Displays
Digital
Analog bar graph
digit, 2000 count LED. Overrange
indication is 1, blank, blank, blank.
31/2
10 segment LED intensity modulated bar
graph display of digital readout. Segments are logarithmically activated with
approximately 2.5 dB,'segment.
MISCELLANEOUS
Power consumption
Approximately 24 watts.
Internal power supplies
+15
Nominally + 15.1 V ±3%,
15
Nominally -15.1 V ±5%.
+5
Nominally + 5.25 V ± 5%.
Fuse Data
F4060
3 AG, 1 A, 250 V, fast blow.
F4061
3 AG, 1 A, 250 V, fast blow.
F4062
3 AG, 1.5 A, 250 V, fast blow.
Recommended adjustment
interval
1000 hours or 6 months, whichever
occurs first.
Warm-up time
20 minutes; 60 minutes after storage
in high humidity envi ron ment.
2.1.6
TM 09361A-12
Specification—F7523A1 Mod WO—AA 501A Mod WQ
Table 2,1.2
ENVIRONMENTAL CHARACTERISTICS
Description
Characteristics
Meets MIL-T-288000, Class 5.
Temperature
Operating
Non-Operating
Humidity
0°C to +50°C.
-40°C to + 75°C.
95% RH, 0 to + 30°C.
Meets MIL-T-288000, Class 5.
75% RH, to +40°C.
45% RH, to + 50°C.
Exceeds MIL-T-288000, Class 5.
Altitude
Operating
4.6 km (15,000 ft).
Non-Operating
15 km (50,000 ft).
Vibration
0.38 mm (0.015") peak to peak, 5 Hz to
55 Hz, 75 minutes.
Meets MiL-T-288000, Class 5.
Shock
30 g's (1/2 sine), 11 ms duration,
3 shocks in each direction along 3 ma or
axes, 18 total shocks.
Meets MIL-T-288000, Class 5.
Bench Handling
(plug-in only)
12 drops from 45°, 4" or equilibrium,
whichever occurs first.
Meets MIL-T-288000, Class 5.
Package Product Vibration and
Shock (plug-in only)
Qualified under National Safe Transit Association Preshipment Test Procedures
1 A-B-1 and 1A-B-2.
Electromagnetic Susceptibility
Within limits of MIL-STD-461B (April 1, 1980) Class B.
Electromagnetic Interference
Within limits of F.C.C. Regulations, Part 15, Subpart J. Class A; VDE 0871
category B, VDE 0875; and MIL-STD-461 B (April 1, 1980) Class B.
Electrostatic Immunity
! At least 15 kV discharge from 500 pF in series with 100 £2 to instrument case or
any front panel connector without damage or permanent performance
degradation (input terminals limited to 1 0 kV).
2.1.7
Specification— F7523A1 Mod WC —AA 501A Mod WC
TM 09361A-12
Table 2.1.3
PHYSICAL CHARACTERISTICS
Characteristics
Description
Maximum Overall Dimensions
Height
126.0 mm (4.96 inches).
Width
131.2 mm (5.16 inches).
Length
285.5 mm (11.24 inches).
Net Weight
Approximately equal to 2.04 kg (4.5 lbs.).
Finish
2.1.8
Front Panel
Plastic-aluminum laminate.
Chassis
Anodized aluminum.
TM 09361A-12
Pa rt 2—F7523A1 Mod WO
OPERATING INSTRUCTIONS
Controls, Connectors, and Indicators
All controls, connectors and indicators (except for the
rear interface connector) required for operation of the
AA 501A are located on the front panel. Fig. 2.2.1 provides a brief description of all front panel controls, con nectors. and indicators.
Ol INPUT RANGE
Selects input voltage range or AUTORANGE. The
three most sensitive ranges operate in the LEVEL
FUNCTION only.
2O DECREASE RANGE
When this light is illuminated, reduce the INPUT
LEVEL RANGE until the light goes out. If the FUNCTION selected is THD + N or IMD a flashing light
indicates insufficient input signal level for distortion
measurements.
3O INCREASE RANGE
When this light is illuminated, increase the INPUT
LEVEL RANGE until the light goes out.
+ INPUT
Differential input terminal. Positive going input signal provides positive going output signal at INPUT
MONITOR.
5O - INPUT
Differential input terminal. Negative going input
signal provides positive going output at INPUT
MONITOR.
6O RELEASE LATCH
(^7 LEVEL
Button in selects input level measuring function.
8O VOLTS
Button in selects voltage units for level function.
9O dBm 600 fl
Button in selects dBm units for level function. 0 dB
reference is 0.7746 V corresponding to 1 mW into
600 D.
10 dB RATIO
Button in selects dB ratio, with respect to preset
level, as units for level function.
11 PUSH TO SET 0 dB REF
Push button to set display to 0 with input signal
applied to INPUT terminals in LEVEL FUNCTION.
dB RATIO and LEVEL push buttons must be in for
this feature to operate.
REAR INTFC-INPUT
Button in selects rear interface input, button out
selects front panel input.
13 RESPONSE
Button in gives RMS detection (responds to the rms
value of the input waveform). Button out gives
average detection or calibrated for sine waves.
14 THD+N
Button in selects total harmonic distortion function.
15 I MO
Button in selects intermodulation distortion
function.
16 AUTO RANGE
Button in selects automatic distortion range selection (0.2% to 100% full scale).
17 20%
Button in selects full scale distortion readout of
20% with 0.01 % resolution.
2.2.1
Operating Instructions—F7523A1 Mod WQ—AA 501A Mod WQ
TM 09361A-12
7813-- 1
Fig. 2.2.1. Front Panel Controls and Connectors.
2.2.2
'J
TM 09361A-12
Operating Instructions—F7523A1 Mod WQ—AA 501A Mod WQ
@2%
Button in selects full scale distortion readout of 2%
with 0.001 % resolution.
19 0.2%
Button in selects full scale distortion readout of
0.2% with 0.0001 % resolution.
20 dB
Selects single equivalent 0 dB to -100 dB distortion
display range with 0.1 dB resolution.
21 400 Hz HI PASS
Button in connects filter before detector circuit in all
function.
22 80 kHz LO PASS
Button in connects filter before detector circuit in all
functions.
23 30 kHz LO PASS
Button in connects filter before detector circuit in all
functions.
24 `C MSG' WTG FILTER
Button in connects filter before detector circuit in all
functions.
30 LED BAR GRAPH
Provides approximate analog display of the digital
display for nulling and peaking. Each segment represents approximately 2.5 dB.
31 DIGITAL
DISPLAY
1
3 /2 digits. Overrange indication is a blanked display with the numeral 1 in the most significant digit
position.
32 V
Illuminated when display units are volts.
33 mV
Illuminated when display units are millivolts.
34 µV
Illuminated when display units are microvolts.
35 %
Illuminated when display units are percent.
dBm
Illuminated when display units are dB.
37 dB
Illuminated when display units are dB.
Instrument Connections
25 EXT FILTER
Button in allows connection of external filter
between FUNCTION OUTPUT and AUXILIARY
INPUT in ali functions.
26 INPUT MONITOR
Provides a buffered sample of the input signal
27 FUNCTION OUTPUT
Provides a sample of the selected FUNCTION signal additionally processed by selected filters.
28 AUXILIARY INPUT
Provides input to the detector circuit when the EXT
FILTER button is pressed.
29 GROUND
Provides front panel chassis ground connection.
To make connections to the AA 501 A Mod WQ, refer to
Fig. 2.2.2. Connections can be made to the rear interface connector. However, low level or distortion
measurements made through the rear interface may be
degraded due to cross talk. To measure signals connected to the front panel make certain the INPUT push
button is out. To select the rear interface signal input,
press the INPUT push button.
CAUTION
Maximum front panel input voltage is 300 V
peak, 200 V rms either input to ground or differentially. Maximum rear interface input is 42 V
peak and 30 V rms.
The AA 501 A Mod WQ input circuitry is protected against
accidental overloading. This circuitry will recover without damage from continuous 120 V rms (30 minutes at
200 V rms) overloads in any INPUT RANGE setting.
2.2.3
TM 09361A-12
Operating Instructions—F7523A1 Mod WQ—AA 501A Mod WQ
• q q
0i q
0 q
q ®
©I q
n
L
•
J
SHIELDED TWISTED PAIR
FOR MAXIMUM HUM
/ REDUCTION
DUT
COAXIAL
CABLE
INPUT GROUND
OUTPUT
FROM
OSCILLATOR
LOAD
7813-12]
Fig. 2.2.2. Typical connections for distortion measurements.
In most cases, for maximum hum rejection, follow the
cabling and grounding as shown in the figure. Shielded,
twisted pair offers maximum hum and radio frequency
interference rejection. Cable shielding, If used, should
be grounded only at the AA 501 A Mod WQ front panel
ground post. Use shielded cable to connect the output of
an oscillator, external to the device under test, to the
input of the device. Generally, to avoid possible ground
loops, if the device under test has one side of the input
grounded, float the output of the external oscillator. If the
input to the device under test is floating (not chassis
grounded) select the grounded mode for the output of
the oscillator. Terminate the output of the device under
test in Its recommended load impedance, or the load
i mpedance specified in the appropriate standard.
2.2.4
Level Measurements
In the LEVEL function the AA 501 A Mod WQ operates as
a wide band ac voltmeter. The Specification section of
this manual contains the operating parameters. The
meter is rms calibrated and either rms or average
responding, depending on the position of the
RESPONSE push button.
Press the FUNCTION LEVEL push button. The top three
buttons to the left of the FUNCTION push buttons select
readout units as VOLTS, dBm 600 S2, or dB RATIO. For
example, to measure voltage, press the VOLTS push
button. If the INCREASE RANGE LED is illuminated,
adjust the INPUT LEVEL RANGE control to the higher
TM 09361A-12
Operating Instructions—F7523A1 Mod WQ—AA 501A Mod WQ
ranges until the LED goes out. If the DECREASE RANGE
LED is illuminated, turn the INPUT RANGE control
counterclockwise until the DECREASE RANGE LED
goes out. Readings are useable as long as the display is
not overranged, however, for specified accuracy, the
DECREASE RANGE LED must also be off Overrange is
indicated by a blank display with the numeral 1 in the
most significant digit slot.
If the INPUT LEVEL RANGE switch is placed in the AUTO
RANGE position, the input level is adjusted automatically. The LEDs (VOLTS, mVOLTS or µVOLTS) automatically illuminate showing the proper display units.
Notice that the three most sensitive ranges on the INPUT
LEVEL RANGE control operate in the LEVEL FUNCTION
only.
When the dBm 600 d2 push button is pressed, the LED
opposite dBm on the display indicates the display units.
The reference level for this measurement, 0 dBm, is
0.7746 V corresponding to 1 mW dissipated in 600 fl.
The INPUT LEVEL RANGE switch operate as previously
described.
The dB RATIO mode permits direct amplitude ratio
measurements of two input signals. When the dB RATIO
push button is pressed, the LED opposite the dB nomenclature on the display illuminates. To use this feature,
press the dB RATIO push button. To establish the input
signal as 0 dB reference, push the PUSH TO SET 0 dB
REF push button and notice that the display reads all
zeros.
MOD WQ provides several internal filters, as well as
facilities for connecting external filters. For information
on their operation and use, see the text under Filter in this
section of this manual.
Disto rt ion Measurements
Distortion is a measure of signal impurity. It is usually
expressed as a percentage of dB ratio of the undesired
components to the desired components. Harmonic
distortion is simply the presence of harmonically related
or integral multiples of a single pure tone called the
fundamental, and can be expressed for each particular
harmonic. Total harmonic distortion, or THD, expresses
the ratio of the total power in all significant harmonics to
that in the fundamental.
The transfer (input vs output) characteristics of a typical
device is shown in Fig. 2.2.3. ideally this is a straight line.
A change in the input produces a proportional change in
the output. Since the actual transfer characteristic is nonli near, a distorted version of the input waveshape
appears at the output. The output waveform is the
projection of the input sine wave on the device transfer
characteristic as shown in Fig. 2.2.4. The output
waveform is no longer sinusoidal, due to the nonlinearity
of the transfer characteristic. Using Fourier analysis it
can be shown that the output waveform consists of the
ordinal input sine wave, plus sine waves at integer
multiples of the input frequency. These harmonics represent nonlinearity in the device under test. Their amplitudes are related to the degree of nonlinearity.
Release the 0 dB REF push button. As the amplitude of
the signal is changed, the display reads the dB ratio of
the input signal to the reference signal amplitudes.
There are many useful applications for the dB RATIO
mode in measurements of gain-loss, frequency
response, S/N ratio, etc. For example, the comer
frequency of a filter maybe quickly checked. Set the test
frequency to some midband value and set the zero dB
reference. Adjust the test frequency until the display
reads -3 dB; this is the comer frequency of the filter.
Gain measurements may be simplified by using this
feature. Set the device to be tested as desired and connect the AA 501 A Mod WQ input to the input of the device
under test. Press the PUSH TO SET 0 dB REF push
button. Then connect the input of the AA 501 A Mod WQ to
the device output and read the gain or loss directly from
the display.
When measuring signal to noise ratio or making noise
level measurement, it is often desirable to employ a frequency dependent weighting network. The AA 501A
OUTPUT
F
i ce/ IDEAL
/^—DEVICE
TYPICAL
DEVICE
i
i
INPUT
7813-04
Fig. 2.2.3. Transfer characteristics of an audio device.
2.2.5
Operating Instructions—F7523A1 Mod WQ—AA 501A Mod WQ
TM 09361A-12
781
Fig. 2.2.4. THD test of transfer characteristics.
A total harmonic distortion measurement inevitably
includes effects from noise to hum. The term THD + N
has been recommended' to distinguish distortion
measurements made with a distortion analyzer from
those made with a spectrum analyzer.
A spectrum analyzer allows direct measurement of each
harmonic. The spectrum analyzer technique involves
making a narrow-band measurement of each harmonic,
and then performing a root-mean-square summation of
the harmonics to produce a THD number uninfluenced
by broadband noise and other components such as ac
I HF-A-202 1978, Standard Methods of Measurement for
Audio Amplifiers, The Institute of High Fidelity, Inc., 489 Fifth
Avenue, New York, N.Y. 10017.
2.2.6
hum or interference. However, it is relatively complex,
ti me consuming, and requires interpretation of a graphic
display.
An appealing feature of the THD + N (total harmonic distortion plus noise) measuring technique is that the meter
presents one number integrating harmonics, broadband
white noise, hum, and specific interfering signals.
Distortion analyzers can quantify the nonlinearity of a
device or system. A distortion analyzer removes the
fundamental of the signal investigated and measures the
remainder. See Fig. 2.2.5. Because of the notch filter
response, any signal other than the fundamental
influences the measurement.
TM 09361A-12
Operating Instructions—F7523A1 Mod WQ—AA 501A Mod WQ
A
FUNDAMENTAL
A
FUNDAMENTAL
liii
_____
IF DEVICE
UNDER
TEST
L
F
/
OSCILLATOR
FUNDAMENTAL
ELIMINATED
A
/J
Y
FILTER
i
i
II
/
I/
F
AC TO DC
CONVERTER
READOUT"
7813-05
Fig. 2.2.5. Block diagram of a basic harmonic distortion analyzer.
Distortion Measurement Procedure
Al! of the controls found on a traditional distortion
analyzer are automated on the AA 501A Mod `NQ. It is
only necessary to connect to the DUT and set the INPUT
RANGE and DISTORTION RANGE switches to AUTO
RANGE. Press THD + N andwait briefly for a reading.
Minimum input signal amplitude for valid distortion
measurements is 60 mV. To provide greater flexibility the
instrument may be manually operated as described in
the following paragraphs.
Adjustment of the input level range control is the same as
for level measurements. Manually setting the INPUT
RANGE control to the correct scale ensures that the input
is within the 10 to 12 dB range of the internal auto setlevel circuitry. The range LEDs must be extinguished to
make readings to specified accuracy. The 200 µV, 2 mV
and 20 mV ranges do not operate in the distortion
function and a flashing Decrease Range LED indicates insufficient input signal level for distortion
measurements.
To manually select a distortion range, press the THD + N
button and the desired range button. Selection of AUTO
RANGE causes the instrument to autorange the
distortion readout. The remaining range push buttons
cause the instrument to stay in these ranges without
autoranging. This may reduce the measurement time
slightly if the approximate reading is already known. This
is useful in production line testing or in the testing of low
distortion equipment. The dB display is effectively a
single range; however, internal instrument operation is
identical to AUTO RANGE.
When making distortion measurements, the RESPONSE
button should normally be in the RMS position. Current
distortion measurement standards require the use of rms
reading instruments by specifying power summation of
each of the components. The AVG response may be
used when making comparisons with readings taken
with older distortion analyzers. However, it may read up
to 25% (2 dB) lower than rms response when noise is
significant and even lower with high crest factor distortion signals (characteristic of crossover or hard-clipping
nonlinearities).
For frequencies below 20 kHz, the residual wideband
noise in the measurement may be reduced by activating
the 80 kHz LO PASS filter. If hum (line related components) are Interfering with the measurement, they may
be reduced with the 400 Hz HI PASS filter. This filter
should not be employed with fundamental frequencies
below approximately 400 Hz because of additional error
due to rolloff. For more information, see text under Filters
section of this manual.
2.2.7
Operating Instructions—F7523A1 Mod WQ—AA 501A Mod WQ
TM 09361A-12
IM Distortion Measurements
High Disto rt ion Measurement Limitations
Another measurement of disto rt ion investigates the interaction of two or more signals. Many tests have been
devised to measure this interaction. Four common stan-
NOTE
Care must be taken to ensure proper locking for
input signals with 10% or greater noise or non
harmonic components, because the AA 501A
Mod WQ automatically tunes and nulls out the
fundamental frequency prior to making a THD
+ N measurement.
dards are SMPTE , DIN , CCIF , and Twin-Tone. The
3
4
5
AA 501A Mod WQ is capable of automatically selecting
and performing all three tests.
To measure intermodulation distortion (IMD), according
to SMPTE and DIN standards, the device under test is
In those applications which require higher THD + N
measurements (for example, SINAD testing) the internal
2
excited with a low frequency and high frequency signal
simultaneously (Fig. 2.2.6). The output signal is high-
circuitry will remain locked to noise levels of approxi-
pass filtered to remove the low frequency component.
mately 30%, after it is initially given a clean signal. To
The high frequency tone is then demodulated, as an AM
perform a SINAD test, the receiver under test is first given
a high level modulated rf input. The AA 501A Mod WQ
will lock onto the audio signal at the demodulated output. The rf level feeding the receiver is then reduced until
radio signal. The demodulator output is low-pass
filtered to remove the residual carrier (high frequency)
components. The amplitude of the low frequency
a -12 dB (25%) THD + N reading is obtained on the
AA 501 A Mod WQ and becomes a measure of the
receiver's sensitivity.
2 Defined In Electronic Industries Association Standard No. RS
204A, July 1972, Electronic Industries Association, Engineering Depa rtment, 2001 Eye St. N. W., Washington, D.C. 20006.
A
modulation is displayed as a percentage of the high
frequency level.
3 Society of Motion Picture and Television Engineers, Standard No. TH 22.51, 862. Scarsdale Avenue, Scarsdale, N.Y.
10583.
4 Deutsches ilntitutfur Normung a V, No. 45403 Bla tt 3 and
4, January 1975, Beuth Verlag GmbH, Berlin 30 and
Koln 1.
5 International Telephone Consultative Commi ttee.
A
A.
A
F
olllll
l
I
l
D°-,►I__ F
I
I
II',
I'
—
F
'1 41
III'
^
II;I'
111111 11I^
III.
F
I^",1.;,f;.
^
lilll
sll
F
I
I
^^
I
I
ICI
III,.
I
I^II^
—
I
uh
I t
II^II
.
III^^;;III
I,I,
I^^ ^
IIIIIV
II
II`
I
781
Fig. 2.2.6. Block diagram of basic IM analyzer.
2.2.8
TM 09361 A-12
Operating Instructions—F7523A1 Mod WQ—AA 501A Mod WQ
As shown in Fig 2.2.7 when this composite signal is
applied to the device, the output waveform is distorted.
As the high frequency tone is moved along the transfer
characteristic by the low frequency tone, its amplitude
changes. This results in low frequency amplitude modulation of the high frequency tone. This modulation is
apparent in the frequency domain as sidebands around
the high frequency tone. The power in these sidebands
represents nonlinearlty in the device under test.
The amplitude ratio of low to high frequencies should be
between 4:1 and 1:1. The AA 501A Mod WQ circuitry
automatically adjusts calibration to compensate for the
selected test signal ratio. Some additional range is provided in this circuitry to enable measurement of devices
with nonflat frequency response.
TRANSFER (INPUTCHARACTERISTI
TEST DEVIC
SMPTE standard test frequencies are 60 Hz and 7 kHz.
The DIN standard is virtually identical to the SMPTE standard except for the two frequencies used. They may be
any pair of octave band center frequencies, with the
upper at least eight times as high as the lower (250 Hz
and 8 kHz are most common). The AA 501 A Mod WQ can
accept a wide range of test frequencies as shown In the
Specifications section.
CCIF difference frequency distortion is measured with
two high frequency sine waves driving the device under
test. Both are of equal level and closely spaced In
frequency- Nontinearities in the device under test cause
the sine waves to cross modulate. This creates new signals at various sum and difference frequencies from the
inputs. For example, the commonly used 14 kHz and
15 kHz test frequencies produce 1 kHz, 13 kHz, 14 kHz,
15 kHz, 16 kHz, 28 kHz, etc.
PUT
RTED)
^^^Itih1
7813-071
Fig. 2.2.7. IM test of transfer characteristics in time and frequency domain.
2.2.9
Operating Instructions—F7523A1 Mod WQ—AA 501A Mod WQ
The user could measure each new component with a
tunable filter such as a spectrum analyzer; however, this
is usually limited to an 80 dB dynamic range and is very
tedious. In many systems and especially those with
asymmetric non-linearities, a good measure of this
distortion may be obtained by investigating only the difference frequency (in this example 1 kHz) If only the low
frequency component is measured, It is called a COIF
second order difference frequency distortion test.
To measure two tone difference frequency distortion, the
device is excited with two input signals as described
above. The output of the device is low-pass filtered to
remove the two test tones and extract the difference frequency product. The level of this component is
expressed as a percentage of the high frequency signals. The AA 501A Mod WQ CCIF difference frequency
mode will accept any pair of input frequencies which are
within limits as listed in the Specification section. The
amplitudes of the two signals should be equal.
I M Distortion Measurement Procedure
Intermodulation and THD testing are similar, using the
AA 501A Mod WQ. After connecting the appropriate
signal source to the DUT, set the INPUT RANGE as
described in theTHD section. Press the IMD FUNCTION
button and select a distortion range. Selecting AUTO
RANGE or dB provides automatic ranging. The AA 501A
Mod WQ accepts SMPTE, DIN, CCIF, and ',rein-Tone
difference frequency test signals. The AA 501 A Mod WQ
circuitry automatically adjusts calibration to compensate for the selected test signal ratio. Some additional
range is provided in this circuitry to enable measurement
of devices with nonflat frequency response. Selection
between the necessary analyzing circuits is accomplished automatically for IMD levels less than 20%,
based upon the spectral content of the test tones. (There
is a movable jumper inside the AA 501A Mod WQ to
allow defeating the automatic test selection circuitry for
special applications requiring IMD measurements in
excess of 20%. Refer any jumper changes to qualified
service personnel.)
The LO PASS filter may be selected in the IMD mode but
will have little or no effect. The 400 Hz HI PASS and the
WEIGHTING filters will cause erroneous readings
because the IMD components of interest generated by
the tests fall between 50 Hz and 1 kHz. These filters,
when activated in the IMD mode, may attenuate some of
the frequency components being measured and should
be avoided.
2.2.10
TM 09361A-12
Filters
The five buttons along the right edge of the instrument
allow selection of four built-in frequency weighting filters
plus an external filter, as desired. See Fig. 2.2.8 for
response curves of the various filters. The 400 Hz,
30 kHz, and 80 kHz filters are both 3-pole (18 dB per
octave rolloff) Butterworth alignment. The C MSG WTG
filter weights the noise according to its perceived annoyance to a typical listener of standard telephone service.
They are placed in the measuring circuitry immediately
before the average or rms detectors. These filters are
functional in all modes of operation. They also affect the
signal at the FUNCTION OUTPUT connector.
To prevent inaccurate results, check the position of all filter push buttons before making measurements. Filtering
takes place after all gain circuits. When operating in the
manual distortion ranges with a filter selected, it is possible to overload part of the instrument, even though the
display is not overranged. This may be checked by
releasing the filter push buttons and checking the
display for overrange or by pressing the AUTO RANGE
push button.
The 400 Hz Hi PASS filter is used to reduce the effects of
hum on the measurement. Although the differential input
and common mode rejection of the AA 501 A Mod WQ
reduce the effects of ground loops, extremely bad
measurement conditions may require use of this filter.
The DUT may also generate an undesirable amount of
hum, limiting the noise and distortion residuals obtainable. This filter may be used when measuring harmonic
distortion of signals at about 400 Hz or greater, but
should not be used when measuring levels at
frequencies less than 1 kHz, nor when measuring intermodulation distortion.
The 30 kHz LO PASS filter provides bandwidth limiting for
broadcast proof of performance testing. It is also useful
for unweighted noise measurements on audio equipment, providing an equivalent noise bandwidth of
31.5 kHz. When the 30 kHz filter is used, the 80 kHz filter
is disabled
Use of the 80 kHz LO PASS filter reduces the effects of
wideband noise and permits measurement of lower
THD + N for input signals up to 20 kHz. For 20 kHz
inputs, it allows measurement of harmonics up to the
TM 09361 A-12
Operating Instructions—F7523A1 Mod WQ—AA 501A Mod WQ
—
15
_____
_______
________
______ ______
______
+10
+5
OdB
5
^f
4tir
0 -
10
1 5
20
25^
30'
v``
^^v
^^
35
k^
Q
-a0
r
0^
45
V
p0
55
-65
-70
10 Hz
i
20
30
50
100 Hz
200
300
500
—°--
----1 kHz
2
5
1 0 kHz
20
30
50
1 00 kHz
7813-18
Fig. 2.2.8. Response cu rv es for AA 501A Mod WQ filters.
fourth order. Do not use this filter If harmonic components
above 80 kHz are of interest. When checking noise, the
80 kHz filter may be used to reduce the measurement
bandwidth.
The C message weighting filter is used for measurement
of noise in voice-frequency communications circuits.
The filter is designed to weight noise frequencies in proportion to their perceived annoyance effect fortelephone
service.
Connections for an external filter are also provided.
Press the EXTERNAL FILTER push button. Connect the
external filter between the FUNCTION OUTPUT and the
AUXILIARY INPUT. One application for the external filter
is selective measurement of individual harmonics or
components of an Input signal. This may be
accomplished using a unity gain bandpass filter as an
external filter and adjusting the frequency to the
harmonic desired.
Displays
The AA 501A Mod WQ provides two display forms for
manual measurements. The digital readout displays the
selected function with units. Overrange Indication
blanks all digits and displays a numeral 1 in the most significant digit slot.
For rapid nulling or peaking applications, the digital display is supplemented by an uncalibrated LED bar graph
for an analog meter-like display. The bar graph
responds logarithmically, with each segment representing approximately a 2.5 dB change in the selected
function. Additionally, the intensity of the segments is
modulated between steps permitting resolution of
changes as small as 0.5 dB. The range of the bar graph Is
determined by the measurement range in use. When
using this feature it may be desirable to select a manual
range to prevent confusing displays caused by
autoranging.
2.2.11
TM 09361A-12
Operating Instructions—F7523A1 Mod WQ—AA 501A Mod WO
Monitoring
The interface capabilities of the AA 501A Mod WQ may
aid considerably in the interpretation of measurements.
Figure 2.2.9 shows an optional oscilloscope for visual
AUXILIARY
INPUT
15V pk MAX
AA 501A Mod WQ
DISTORTION ANALYZER
monitoring. If connected as shown, channel 1 displays a
sample of the input signal and channel 2 displays the
distortion components when In the IM or THD + N
function.
OSCILLOSCOPE
FUNCTION
OUTPUT
INPUT
MONITOR
INPUT
I
II
CHI CH 2
COAXIAL
/ CABLES
SHIELDED TWISTED PAIR
FOR MAXIMUM HUM
REDUCTION
COAXIAL
CABLE
INPUT GROUND
OUTPUT
N
FROM
OSCILLATOR
LOAD
7813-1
Fig. 2.2.9. Typical connections for distortion measurements with monitoring.
2.2.12
TM 09361A- 12
Operating Instructions—F7523A1 Mod WQ—AA 501A Mod WQ
The INPUT MONITOR connector provides a fixed amplitude version (approximately equal to 1 V rms) of the input
signal for input signals of 50 mV or greater. This allows
display of the input signal on an oscilloscope, without
constantly readjusting the oscilloscope sensitivity. At
input levels below about 50 mV the INPUT MONITOR
signal is approximately 26 dB (gain of approximately
equal to 20) above the input signal level.
The FUNCTION OUTPUT is taken after the distortion
measurement and high gain amplifier circuitry. It can be
used for monitoring the signal read on the display. The
signal at the FUNCTION OUTPUT connector is 2 V for a
full scale reading on the display. In the level function this
connector becomes an amplified version of the input signal. The gain from the input to this output is dependent on
the LEVEL RANGE switch, and is given in Table 2-1.
When the AA 501A Mod WQ is used as a constant gain
differential amplifier, the INPUT RANGE switch must be
set to a fixed range. In the distortion function this output
can be displayed on an oscilloscope to view the distortion components. This output may also be used to drive
a spectrum analyzer or selective voltmeter for examining
the individual harmonics or modulation products. When
an oscilloscope is used, the triggering signal is best
taken from the sync output on the oscillator. If this is not
possible (for example, in tape recorder or Telco link testing) it should be obtained from the INPUT MONITOR
connector on the AA 501A Mod WQ.
One interesting use of the Function Output and Input
Monitor signals is to investigate the nonlinearities of the
transfer function of a DUT with the THD + N mode. For
this measurement, the FUNCTION OUTPUT drives the
vertical input of an oscilloscope while the INPUT
MONITOR drives the horizontal. The resulting display is
similar to Fir. 2.2.10, and represents the deviation from
li nearity of the transfer characteristic. In other words, it
represents the transfer characteristic after the best fit
straight line is removed. This can be particularly useful in
diagnosing sources of nonlinearity such as clipping,
crossover, etc. If the device under test has large amounts
of phase shift at the test frequencies it may be necessary
to introduce compensating phase shift into the horizontal channel. Since the FUNCTION OUTPUT is taken
afterthe filters, they will affect the signal seen at this connector. The vertical scale is the deviation from the best fit
li ne and is related to the distortion range and vertical
sensitivity of the oscilloscope.
Table 2.2.1
Gains from INPUT terminals to
FUNCTION OUTPUT connector for various
settings of the INPUT LEVEL RANGE control
LEVEL RANGE
Setting
Gain to FUNCTION
OUTPUT
200 V
-40 dB
60 V
-- 30 dB
20 V
-20 dB
6V
-10 dB
2V
0dB
600mV
+10dB
200 mV
+20 dB
20 mV
+40 dB
2 mV
+ 60 dB
2004V
+80 dB
Fig. 2.2.10. Oscilloscope display of deviation from
linearity.
2.2.13
TM 09361A-12
Section 3
SG 505 Mod WQ
Test Signal Oscillator
F7523A1 Mod WO SG 505 Mod WQ
Figure 3.1.1. The SG 505 Mod WO Oscillator.
3.1.0
TM 09361 A-12
TM 09361A-12
Part 1 —F7523A1 Mod WQ—SG 505 Mod WQ
SPECIFICATION
Performance Conditions
Introduction
The SG 505 Mod WQ Oscillator generates an ultra low
distortion sine wave over the frequency range from 10 Hz
to 100 kHz This signal can be floated or referenced to
chassis ground. The oscillator also provides a fixed
amplitude ground referenced sine wave signal at the
SYNC OUT connectorthat is identical infrequency to the
signal from the OUTPUT connector. Versions of both
output signals are available at the rear interface
connector.
The SG 505 Mod WQ is designed to operate in the
left-most compartment of the TM 504A Mod WQ Series
Power Module..
The electrical characteristics are valid only if the SG 505
Mod WQ has been calibrated at an ambient temperature
of +20°C to +30°C and is operating at an ambient
temperature of 0°C to +50°C, unless otherwise noted.
Items listed in the Performance Requirements column of
the Electrical Characteristics are verified by completing
the Performance Check in the Calibration section of this
manual. Items listed in the Supplemental Information
column are not verified in this manual. They are either
explanatory notes or performance characteristics for
which no limits are specified.
Table 3.1.1
Electrical Characteristics (Front Panel)
Characteristics
Performance Requirements
Supplemental Information
FREQUENCY
Range
Vernier Range
Dial Accuracy
10 Hz to 100 kHz in four overlapping
bands.
Typically 9 Hz to 110 kHz. Nominal range of
each band is 0.90 to 11.0.
a + I % of frequency setting.
i ±3% of setting with vernier at center.
Drift
Typically less than 0.01 %/°C and
0.03 %/hour.
OUTPUT LEVEL
Calibrated Steps
+ 10 dBm to -60 dBm into 600 S2 in
eight 10 dB steps, ±0.2 dB at 0 dBm
and 1 kHz.
Step Accuracy
±0.1 dB/10 dB step.
Stability
Typically better than 0.01 dB/°C and
0.03 dB/hour.
Variable Range
2 +2.2 dB to <-10 dB from calibrated
position.
Maximum Output
210 dBV (+ 12.2 dBm) or 3.16 V rms
into 600 a.
Setting Time
2 6 V rms unloaded.
5 5 seconds to 0.2 dB of final value,
20 Hz-100 kHz, typically <3 seconds
above 100 Hz. Worst case transient overshoot is 5 3 dB.
3.1.1
TM 09361A-12
Specification—F7523A1 Mod WO—SG 505 Mod WQ
Table 3.1.1 (cont)
Characteristics
Performance Requirements
Supplemental Information
LEVEL FLATNESS
(1 kHz reference)
10 Hz-20 kHz
±0.1 dB,
20 kHz-100 kHz
±0.2 dB (exclude -60 dB OUTPUT
LEVEL attenuator range).
Refer to Buffered Main Output load
i mpedance limitation under Electrical
Characteristics (Rear Interface).
DISTORTION
(R L ? 600 l)
10 Hz-50 kHz
5 -80 dB THD.
50 kHz-100 kHz
S -60 dB THD.
OUTPUT
I mpedance
600 c2 ±2%
Floating or grounded through approximately
30 fl. Output impedance does not change
with OUTPUT ON/OFF selection.
51 % of output ac m-is voltage.
Dc Offset
Maximum Floating
Voltage
±30 V peak. (0.01 µF between output cornmon and chassis ground in floating mode.)
Line Related Cornmon Mode Output
Voltage In Floating
Mode
Typically 5 50 mV rms into an open circuit.
SYNC OUTPUT
Signal
I mpedance
Sine wave with same frequency as output.
200 mV rms ±20% sine wave to
20 kHz, at least 120 ! .V at 100 kHz.
THD is typically 5 3% and phase shift from
OUTPUT is typically 5 0 , 20 Hz to 20 kHz.
1 kfl, ± 10%, ground referenced and isolated from the main output.
ELECTRICAL CHARACTERISTICS (Rear Interface)
Buffered Main Output
Pins 25A and 26A (common). Fixed output
of m 2 V rms from • 300 ohms. Pin 26a is
electrically connected to front panel OUTPUT
common. To prevent possible instrument
damage, do not float output in excess of
± 30 V peak.
Sync Output
Pins 27B and 28B (ground). Approximately
200 mV rms sine wave identical to front
panel SYNC output signal. Output
i mpedance is approximately 50 fl and
always ground referenced.
3.1.2
TM 09361A-12
Specification—F7523A1 Mod WQ —SG 505 Mod WQ
Table 3.1.2
Miscellaneous
Characteristics
Supplemental Information
Performance Requirements
6 VA or less.
Power Consumption
Calibration Interval
1000 hours or 6 months.
Warm-up Time
20 Mi nutes.
Table 3.1.3
Environmental
Description
Characteristics
Meets MIL-T-28800B, Class 5.
Temperature
Operating
0°C to +50°C.
Non-Operating
-55°C to +75°C.
Humidity
90-95% RH for 5 days cycled to 50°C.
Exceeds MIL-T-288008, Class 5.
Exceeds MIL-T-288008, Class 5.
Altitude
Operating
4.6 km (15,000 ft.)
Non-operating
15 km (50,000 ft.)
Vibration
0.38 mm (0.015") 10 Hz to 55 Hz, 75
minutes.
Meets or exceeds MIL-T-28800B, Class 5.
Shock
30 g's (112 sine), 11 ms, 18 shocks.
Meets or exceeds MIL-T-288006, Class 5,
Bench Handling
45 degrees or 4" or equilibrium, whichever occurs first.
Meets MIL-T-28800B, Class 5.
E.M.C.
MiL-STD 461A/462.
Meets MIL-T-288008, Class 5.
Electrical Discharge
20 kV maximum.
Charge applied to each protruding area of
the product under test except for the output
terminals.
Transportation
Qualified under National Safe Transit Association Preshipment Test Procedures 1A-B-1
and 1A-B-2.
Vibration
25 mm (1 ") at 270 rpm for 1 hour.
Package Drop
10 drops from 91 cm (3 ft.)
3.1.3
TM 09361Al2
Specification—F7523A1 Mod WO—SG 505 Mod WC
Table 3.1.4
Physical Characteristics
Characteristics
Description
I
Finish
Plastic-aluminum laminate front panel.
Net Weight
Overall Dimensions
67,06 mm (2.640") W x 306.36 mm (12.140") D x 126.24 mm (4.970") H.
3.1.4
1.13 kg (2,49 Ibs).
TM 09361A-12
Part 2—F7523A1 Mod WQ—SG 505 Mod WQ
OPERATING INSTRUCTIONS
impedance. FLTG connects the outer conductor to
ground through a capacitor for floating operation.
CONTROLS AND CONNECTORS
FREQUENCY SELECTION
cavTioN
1O FREQUENCY Hz Dial
Provides continuous frequency selection within
each push button selected frequency range.
2O
Multiplier Push Buttons
Select any one of four frequency ranges.
3O
FREQ VERNIER Dial
Adjusts frequency ± 1 % from selected frequency
or SG 505 Mod WQ
GNDEDIFLTG switch is set to GNDED, both
instruments are then at ground reference.
If either SG 505 Mod WR
OUTPUT CONNECTORS
OUTPUT LEVEL SELECTION
4O OUTPUT LEVEL (dBm) Dial
Selects one of eight amplitude level steps,
calibrated in dBm, into a 600 fl load.
5O OUTPUT LEVEL (dBm) CAL Dial
Provides continuous amplitude adjustment above
and below the calibrated OUTPUT LEVEL (dBM)
steps.
O
6 ON-OFF Push Button
Connects or disconnects the signal to the OUTPUT
connector.
7O GNDED-FLTG Push Button
GNDED connects the OUTPUT connector outer
conductor (shield) to chassis ground through a low
O8
OUTPUT Connector
Provides a sine wave signal at a frequency
selected by the FREQUENCY Hz dial and multiplier
push button at an amplitude selected by the
OUTPUT LEVEL.
SYNC OUT Connector
Provides approximately 200 mV rms fixed
amplitude and ground referenced sinusoidal signal
at the same frequency as the OUTPUT signal.
10 Ground Binding Post
Chassis ground.
11 Release Latch
Pull to remove plug-in from the power module.
12 POWER Indicator
Indicator lights when power is applied to instrument
from power module.
3.2.1
Operating Instructions—F7523A1 Mod WQ—SG 505 Mod WO
Fig. 3.2.1. Front panel controls and connectors.
3.2.2
TM 09361A=12
TM 09361A-12
Operating Instructions—F7523A1 Mod WO—SG 505 Mod WQ
OPERATORS FAMILIARIZATION
General Operating Information
With the SG 505 Mod WQ properly installed in the power
module, allow twenty minutes warm-up time for
operation to specified accuracy.
Output Connections
The output of the SG 505 Mod WQ at the OUTPUT
connector is designed to operate as a 600 ( voltage
source working into a 600 D load. At higher frequencies,
an unterminated or improperly terminated output may
reduce amplitude accuracy. Loads less than 600 £1 may
cause waveform distortion To ensure waveform purity,
observe the following precautions:
1.
Use good quality coaxial cables and connectors
2.
Make all connections tight and as short as possible
The signal at the SYNC OUT connector is designed for
use as an external trigger for a counter, oscilloscope, or
other device. This output is approximately 200 mV rms
with a source impedance of 1 kfl, and is always
referenced to chassis ground (even when the main
OUTPUT is floating).
CAUTION
To avoid damage to the SG 505 Mod WQ
circuitry, do not apply a voltage exceeding 30 V
peak with respect to chassis ground, to any
front panel connector or to rear interface
connector pins 14A-28A and 14B-28B.
Frequency Selection
The SG 505 Mod WQ produces a sine wave signal at any
frequency from 10 Hz to 100 kHz. To set the frequency,
set the FREQUENCY Hz dial to the desired frequency
and press the appropriate multiplier push button. The
FREQ VERNIER dial may be used to adjust the OUTPUT
frequency 1 percent above and below the frequency
selected by the FREQUENCY Hz dial and multiplier push
button. With the FREQ VERNIER dial at the center
position, the output frequency produced is the
FREQUENCY Hz dial setting multiplied by the active
multiplier value. Signals at the OUTPUT and SYNC OUT
connectors are of the same frequency. The SYNC OUT
signal can be used as an external signal for monitoring
the OUTPUT, provided no more than approximately
200 mV is required from the SYNC OUT connector.
Output Level Selection
The OUTPUT LEVEL dial selects eight level steps from
+10 dBm to -60 dBm. The CAL control, concentric
within the OUTPUT LEVEL (dBm) dial, permits
continuous adjustment above and below the calibrated
output level ste p s. The signal at the OUTPUT connector
may be ground referenced or floated up to ± 30 V peak,
using the FLTG-GNDED push button. The ON-OFF
push button connects or disconnects the signal at the
OUTPUT connector.
Rear Interface Signals
A fixed level buffered OUTPUT signal is available at rear
interface connector pins 25A and 26A (common). When
the rear interface OUTPUT signal is used, the rear
interface load impedance (pins 25A and 26A) must be
> 1 kfl, to prevent OUTPUT amplitude distortion. The
ON-OFF and FLTG-GNDED push buttons affect the rear
interface output signal as previously described for the
front panel OUTPUT signal.
The signal at the front panel SYNC OUT connector is also
available at the rear interface connector, pins 27B and
28B (ground). The output impedance at these rear
interface pins is approximately 50 R and the signal is
always referenced to ground.
3.2.3
TM 09361A-12
Section 4
SG 505 Mod WR
Oscillator
F7523A1 Mod WQ—SG 505 Mod WR
Figure 4.1.1. SG 505 Mod WR Oscillator.
4.1.0
TM 09361A-12
TM 09361A-12
Part 1 —F7523A1 Mod WQ—SG 505 Mod WR
SPECIFICATION
INTRODUCTION
PERFORMANCE CONDITIONS
The SG 505 Mod WR Oscillator generates an ultra low
distortion sine wave over the frequency range from 10 Hz
to 100 kHz. this signal can be floated or referenced to
chassis ground. The oscillator also provides a fixed
amplitude ground referenced sine wave signal at the
SYNC OUT connector that is identical in frequency to the
signal from the OUTPUT connector.
The electrical characteristics are valid only if the SG 505
Mod WR has been calibrated at an ambient temperature
of +20°C to +30°C and is operating at an ambient
temperature of 0°C to + 50°C, unless otherwise noted
Items listed in the Performance Requirements column of
the Electrical Characteristics are verified by completing
the Performance Check in the Calibration section of this
manual. Items listed in the Supplemental Information
column are not verified in this manual. They are either
explanatory notes or performance characteristics for
which no limits are specified.
The SG 505 Mod WR is designed to be operated in the
second-from-the-left compartment of the TM 504A
Mod WQ Power Module.
Table 4.1.1
Electrical Characteristics
Pe rformance Requirement s
Characteristics
1
Supplemental Information
FRONT PANEL
OUTPUT LEVEL
Calibrated Output
(f =1 kHz)
Maximum output 221 V rms unloaded.
Rs = 600 fl in
CAL detent
Rs = 50 S( just ccw
CAL detent
+ 22 dBm (9.75 V rms) ± 0.2 dB into
6000..
of
Attenuator Step Accuracy
(f-1 k Hz)
j
+ 28 dBm (19.46 V rms) ± 0.3 dB into 600 f.
and at least + 30 dBm (12.25 V rms) into
150 fl.
±0 1 dB for any 10 or 20 dB step Range is +22 dBm to -68 dBm.
change.
Stability
Variable Range
Maximum output with variable out of CAL
position increases to + 22.7 dBm.
Typically better than
0.03 dB/hour.
At least 11 dB.
Setting time
0.01
dB/°C
and
Nominal range is +0.7 dB to < -10dB.
5 5 seconds to 0.2 dB of final value,
20 Hz-100 kHz; typical < 3 seconds
above 10 Hz. Worst case transient overshoot is 5 3 dB.
LEVEL FLATNESS
(1 kHz ref, R L =600 S2)
10 Hz-20 kHz
±0.1 dB.
20 kHz —100 kHz
± 0.2 dB.
Flatness is above 50 kHz unspecified on
-58 dBm and -68 dBm ranges.
4.1.1
TM 09361A-12
Specification—F7523A1 Mod WO—SG 505 Mod WR
Table 4.1.1 (cont)
Characteristics
Supplemental Information
Performance Requirements
OUTPUT
Floating or grounded through approximately 30 S2. Output impedance does not
change with OUTPUT ON/OFF selection.
Capacitance between output common and
chassis ground in floating mode — to
330 pF. .
Impedance
Balanced and selectable: 600
±2%, 150 fl ±3%.
fl Impedance to CT is one-half the selected
impedance.
Balance (if 5 20 kHz, Out- 5 0.5% mismatch of output openput GNDed)
circuit voltages referenced to CT.
Typical Dc Offset
<0.5% of output ac rms voltage.
Maximum Floating Volt
±25 v peak, CT to GND.
DISTORTION (Maximum
Specified Output, AL 2 600 S,)
10 Hz-50 kHz
s -80 dB,
50 kHz-100 kHz
5 -60 dB.
SYNC OUTPUT
Signal
Sine wave 200 mV mis ± 20% to j THD is typicallys 3% and phase shift from
20 kHz; at least 120 mV rms at OUTPUT is typically- 5 0 , 20 Hz to 20 kHz.
100 kHz.
Impedance
Nominally 1 kfl, ground referenced and isolated from main output.
TWIN-TONE TEST SIGNAL
Signal
LF sine wave from SG 505 Mod WQ The test signal is generated by the SG 505
oscillator mixed with normal oscil- Mod WQ IMD test oscillator. SYNC OUT
iator output in a 1 (± 0.5 dB) to 1 signal is low frequency component only.
amplitude ratio.
REAR INTERFACE
Buffered Main Output Pins 25A and 26A. To prevent possible
instrument damage, do not float output in
excess of ± 25 V peak. Output impedance
is approximately 600 (1. For specified distortion performance of the front panel main
output, the rear interface load impedance
must be 21 kfl. This output is intended to
provide an ac signal level reference for gain
measurements. THD is typically 0.035 for
frequencies _520 kHz.
Pins 25A and 26A are balanced and floating; 25A is inverted from + output, 26A
inverted from - output. Signal is attenuated
20 dB and buffered from the actual output
signal at the front panel connector.
Twin-Tone Input From SG 505
Mod WQ
4.1.2
Pins 25B and 26B are used to bring modulating tone in from SG 505 Mod WQ.
TM 09361A-12
Specification—F7523A1 Mod WQ ®SG 505 Mod WR
Table 4.1.2
Miscellaneous
Characteristics
Supplemental Information
Performance Requirements
15 VA or less.
Power Consumption
Internal Power Supplies
+17V
Nominally + 17.0 V ±3%.
-17 V
Nominally -17.0 V ±5%,
Fuse Data
3 AG, 1 A, 250 V, fast blow.
Recommended Adjustment
Interval
1 000 hours or 6 months.
Warm-up Time
20 minutes (60 minutes after storage in
high humidity environm ent).
Table 4.1.3
Environmental
Description
Characteristics
Meets MIL-T-288000, Class 5.
TEMPERATURE
Operating
0°C to +50°C.
Non-Operating
-40°C to +75°C.
HUMIDITY
95% RH, 0°C to 40°C.
Exceeds MIL-T-288000, Class 5.
45%- RH, to 50°C.
BENCH HANDLING
i 12 drops from 45°, 4" or equilibrium,
whichever occurs first.
PACKAGED PRODUCT
VIBRATION AND SHOCK
Qualified under National Safe Transit
Association Preshipment Test
Procedures 1A-B-1 and 1A--B-2.
ELECTROSTATIC IMMUNITY
20 kV maximum charge applied to
instrument case.
ELECTROMAGNETIC
COMPATIBILITY
Within limits of F.C.C. Regulations, Part
15, Subpart J, Class A; VDE 0871; and
MIL-461 A tests RE01, RE02, CE01,
CE03, RS01, RS03, CS01, CS02, and
CS06.
Meets MIL-T-288000, Class 5.
4.1.3
TM 09361A-12
Part 2—F7523A1 Mod WQ—SG 505 Mod WR
OPERATING INSTRUCTIONS
CONTROLS AND CONNECTORS
GND -- FLTG
®
GND connects the CT (common) connector to
chassis ground through a low impedance. FLTG
disconnects the CT (common) from chassis ground
for floating operation. Do not exceed ± 25 V peak
floating potential between the CT connector and
chassis ground.
FREQUENCY SELECTION
1T
FREQUENCY Hz
Provides continuous frequency selection within
each frequency range selected by multiplier push
buttons
CAUTION
O
3O
Multiplier Push Buttons
Select any one of four frequency ranges.
If either SG 505 Mod WR or SG 505 Mod WQ
GNDEDIFLTG switch is set to GNDED, both
instruments are then at ground reference.
VERNIER
Adjusts frequency up to ± 1 % from selected
frequency
10
OUTPUT LEVEL SELECTION
4O OUTPUT LEVEL dBm Into 600 D
OUTPUT CONNECTORS
A
Selects one often amplitude level steps, calibrated
in dBm into a 600 fl load with SOURCE R set to
600 fl.
OUTPUT LEVEL CAL
Provides continuous amplitude adjustment from
the calibrated OUTPUT LEVEL steps. Range is
nominally +0.7 dB3 to <-10 dB relative to the
clockwise CAL detent.
SOURCE R
Selects 50, 150, or 600 S1. source impedance.
Impedance to the CT terminal is one-half the
selected source impedance.
7O
SO
BALANCED OUTPUT
The + BALANCED OUTPUT connector provides a
sine wave signal with the frequency selected by the
FREQUENCY Hz dial and multiplier push buttons
and the amplitude selected by the OUTPUT LEVEL
control. The - BALANCED OUTPUT signal is an
inverted duplicate of the + BALANCED OUTPUT
CT
The CT connector provides the reference point for the +
and - BALANCED OUTPUTS. The CT connector can be
floated above ground or ground--referenced with the
GND-FLTG push button (see 9).
11
SYNC OUT
Provides a fixed-amplitude and groundreferenced sine wave at the same frequency as the
BALANCED OUTPUT signal. This signal is in phase
with the + BALANCED OUTPUT.
TWIN-TONE TEST SIG
Push button in provides a SG 505 Mod WQ IMD test
oscillator sine wave mixed with any selected output
frequency in a 1:1 amplitude ratio.
12
ON-OFF
13 Release Latch
Pull to remove plug-in from the power module.
Connects or disconnects the signal to the
BALANCED OUTPUT connectors (does not switch
CT terminal). The selected source impedance is
retained at the BALANCED OUTPUT connectors
regardless of push button position.
Ground Binding Post
Chassis ground.
14
POWER Indicator
Indicator lights when power is applied to instrument
from power module.
4.2.1
TM 09361A-12
Operating Instructions—F7523A1 Mod Wa—SG 505 Mod WR
Hz
^..
r dBm I
e
TWIN-TONE
.2
tl
I
L,J
WOC1
.n
NC
xiro
11 NLAL
010
s
7
I
ccu
BALANCED OUTPUT _.
DN
I
6iD
RT6
1
i13
vom
1 _
F \^
[^^-—^w^
7813-24
Fig. 4.2.1. SG 505 Mod WR front panel controls and connectors.
4.2.2
TM 09361A-12
Operating Instructions-F7523A1 Mod WQ -SG 505 Mod WR
OPERATORS FAMILIARIZATION
General Operating Information
With the SG 505 Mod WR properly installed in the power
module, allow twenty minutes warm-up time for operation to specified accuracy (60 minutes after storage in
or exposure to a high humidity environment).
Frequency Selection
The SG 505 Mod WR produces a sine wave signal at any
frequency from 10 Hz to 100 kHz. To set the frequency,
press the appropriate multiplier push button and set the
FREQUENCY Hz dial to the desired base frequency. The
VERNIER control adjusts the frequency 1 percent above
and below the frequency selected by the FREQUENCY
Hz dial and multiplier push button. With the VERNIER
control at the center position, the output frequency produced is the FREQUENCY Hz dial setting multiplied by
the active multiplier value. Signals at the BALANCED
OUTPUT and SYNC OUT connectors are of the same
frequency. The SYNC OUT signal can be used as an
external signal for monitoring the frequency of the
BALANCED OUTPUT, provided no more than approximately 200 mV rms is required.
Output Level Selection
A
The OUTPUT LEVEL selects ten level steps from +22
dBm to -68 dBm into a 600 Q load with SOURCE R set to
600 fI If SOURCE R is set to 50 5l., the level will increase
by about 5.3 dB into 600 fl. If SOURCE R is set to 150 fl,
the output level into a 150 fl load is exactly 6 dB higher
than the levels marked on the panel. The OUTPUT LEVEL
CAL control permits continuous adjustment from the calibrated output level steps over the range of approximately + 0.7 dB to <-10 dB from CAL. The signal at the
BALANCED OUTPUT connectors may be ground referenced or floated up to 25 V peak, using the GND-FLTG
push button. The ON-OFF push button connects or
disconnects the signal at the BALANCED OUTPUT
connectors.
Twin-Tone Test Signal
With the TWIN-TONE TEST SIG push button in, a SG 505
Mod WQ IMD test oscillator sine wave is mixed with any
selected frequency at the OUTPUT connectors in a 1:1
amplitude ratio for intermodulation distortion tests. The
composite peak-to peak amplitude is the sum of the two
unmodulated output signals.
Output Connections
CAUTION
To avoid damage to the SG 505 Mod WR
circuitry, do not apply a voltage exceeding
±25 V peak, with respect to chassis ground, to
any front panel connector or to rear interface
connector pins 14A-28A and 14B-28B.
The SG 505 Mod WR is designed primarily as a balanced
source of low distortion sine waves. Thus, it is intended
to be used in systems where the load is also balanced or
differential. The balanced configuration is preferable in
high quality audio applications because of its inherently
superior rejection of common mode signals, such as
induced hum or RF voltage. See Fig 4.2.2A and 4.2.2B.
The SG 505 Mod WR can also be used to drive
unbalanced or single--ended loads if the output is taken
using either the + or - BALANCED OUTPUT connector
as the high side and the CT connector as the low. In this
mode, the output voltage and the source resistance are
both half the calibrated or selected value. See
Fig. 4.2.2E. Driving unbalanced loads from the full
balanced output is not recommended because of
possible degradation due to common mode signals
such as power line hum or noise spikes coupling across
one-half of the output resistance. See Fig. 4.2.2C. Even
when the SG 505 Mod WR is floating unavoidable stray
capacitances within the instrument and those
associated with external cabling can cause small
amounts of these common mode signals to couple to the
load. The coupling magnitude is independent of the
oscillator's output attenuation and will become progressively worse as output amplitude is reduced. Thus, the
common mode noise may dominate any distortion
products in the system, especially at lower output levels.
The stray capacitance can also adversely affect high
frequency flatness. If the SG 505 Mod WR GND-FLTG
push button selects GND in this configuration, then half
the output voltage is short-circuited. See Fig 4.2.2D. To
minimize the contribution of these common mode signals, it is recommended that the SG 505 Mod WR not be
operated in the high power compartment of any TM 500
or TM 5000 series power module. These compartments
provide higher power series-pass transistors with substantially higher stray capacitance to chassis, which
couples larger amounts of common mode signals into
the SG 505 Mod WR.
The GND-FLTG push button either connects the CT connector (common) to chassis ground through approximately 30 d2 or disconnects the CT from chassis ground.
4.2.3
TM 09361A-12
Operating Instructions—F7523A1 Mod WO—SG 505 Mod WR
SG 505 Mod WR
SG 505 Mod WR
BALANCED
OUTPUT
BALANCED
LOADS
+
I
^
^
R
VOUT
+
SOURCE
2
R
SOURCE
R
2
I
I
R LOAD
2
VOUT
2
I
i
I
I
^\
J
I
CT
R LOAD
I
OU1'
2
LOAD
I
OR
1
v CT
V
I
I
BOUT
2
2
I
R LOAD
CSTRAY
2
R SOURCE
2
I
R
SOURCE
I
I
I
L._.__
I
2
— — — — --J
I
V COMMON MODE
A. A balanced system = balanced source + balanced
load.
B. Common mode noise coupled in by stray capacitance
— does not affect balanced load.
SG 505 Mod WR
SG 505 Mod WR
R SOURCE I
VOUT
2
2
V
CT
R LOAD
I
FLTC
OUT
R SOURCE
2
—=2
r
I
0
VOUT
2
CT
`
I
2
-
L
•
R SOURCE
--
--
/1/
R LOAD
I
VOUT
2
R SOURCE
---
I
I
L'.FiD
301!
CSTRAY
t
I
I
C. Grounded load — common mode noise appears
SG 505 Mod WR
R
OUT
2
I
L
D. Single-ended load with GND-FLTG pushbutton in,
connecting CT to chassis ground. The — BALANCED
OUTPUT is effectively sho rt -circuited. Avoid this
condition!
across 1/2 RsouRCE
V
I
J
2
/1/ 2
V COMMON MODE
2—
V
SOURCE
2
I
I
R LOAD
CT
V OUT
2
CSTRAY
R SOURCE
2
t
2
J
^ COMMON MODE
E. Single-ended load with single-ended source common mode signal does not appear at load.
Fig. 4.2.2. Connection configurations.
4.2.4
781
TM 09361A-12
Operating Instructions—F7523A1 Mod WQ—SG 505 Mod WR
Ground the CT wire to the ground of the unit under test
Normally the SG 505 Mod WR is floated to break up any
ground loops between it and the load. Standard practice
is to ground all sources (microphones, etc.) at the unit
under test (console, etc.). See Fig. 4.2.3.
(console) and float the SG 505 Mod WR. The popular
XLR connector allows this type of connections. See
Fig. 4.2.6.
The sine wave at the SYNC OUT connector is in phase
with the + BALANCED OUTPUT and is designed for use
Under some conditions, it may be desirable to ground
the SG 505 Mod WR CT connector. This may be true in a
high RF environment to prevent the CT from floating on
RF induced in the output cables. If it is of sufficient amplitude, such RF may otherwise degrade the linearity of the
SG 505 Mod WR output stages. The best procedure under high RF environment is to use high-quality shielded
cable. Connect the shield to the SG 505 Mod WR CTterminal and a high quality 0.01 to 0.1 4F capacitor connected between the CT terminal and the chassis ground
post. The RF is effectively coupled to ground, while at
low frequencies the SG 505 Mod WR still floats to break
up ground loops. See Fig. 4.2.4. As an alternative, the
GND FLTC push button can be pushed to GND with the
cable's shield connected to the ground post. Doubleshielded cable will improve rejection of RF interference.
See Fig. 4.2.5. Under worst-case conditions, use threeconductor twisted, shielded cable (double-shielded is
preferred) with the shield connected to the chassis
ground post and the three conductors connected to the
+ and - BALANCED OUTPUT and CT connectors.
as an external trigger for a counter, oscilloscope, or other
device. This output has a source impedance of 1 kfl, and
is always referenced to chassis ground (even when the
BALANCED OUTPUT is floating).
Rear Interface Signals
The front panel BALANCED OUTPUT signal (buffered
and attenuated 20 dB) is available at rear interface connector pins 25A and 26A. The signal at these pins is
balanced and floating; 25A is inverted from the front
panel + BALANCED OUTPUT, and 26A is inverted from
the - BALANCED OUTPUT.
PUT. When the rear interface
Buffered Main Output signal is used, the rear interface
load impedance (pins 25A and 26A) must be > 1 kfl to
prevent OUTPUT amplitude distortion. The ON-OFF and
GND--FLT G push buttons affect the rear interface output
signal as previously described for the front panel
BALANCED OUTPUT signal.
SG 505 Mod VV R
UNIT UNDER TEST
1 I
R
'
OUT
SOURCE
I
1
2
!
I
^^
C^
`
I
I I > 0_
I I
I
I
I
I
I
I
I
I I
I I
I
^
R LOAD
VDUT
2
R SOURCE
/77
7813-26
Fig. 4.2.3. Floating oscillator grounded to unit under test to break up ground loops.
4.2.5
Operating Instructions—F7523A1 Mod WQ—SG 505 Mod WR
TM 09361A-12
SG 505 Mod WR
UNIT UNDER TEST
^
________
R
I
SOURCE
2
VOUT
FLTG
I
1
2
CT
Son
CND
OUT
i. 0,01 pF I
?_
T
R
II
—
R LOAD
TO
c
_
SOURC E
' — — -- — — — — — — — —
Z
\ I
^
— —
— —
7813-2 7]
Fig. 4.2.4. Added capacitor between CT and chassis ground improves RFI rejection.
SG 505 Mod WR
UNIT UNDER TEST
+
R
SOURCE
z
BOUT
I
I
I
I
I
I
A
I
I
I
I
!
I
I
I
I
I
I
I
1
FLTC
O
2
--------0
I
^ 30fI
CND
VOUT
2
I
R
SOURCE
CT
I I
I
I
I I
I
I
I I
I I
I
I I
I I
I
I
I
I
R LOAD
I
I
2
7813-28
Fig. 4.2.5. SG 505 Mod WR CT terminal grounded and cable shield connected to ground post. Reduces RF
interference but may cause low frequency ground loop.
4.2.6
TM 09361A.-12
Operating Instructions—F7523A1 Mod WO—SG 505 Mod WR
SG 505 Mod WR
R
V
OUT
2
i
SOURCE
2
UNIT UNDER TEST
I
I
CT
VOUT
2
Ht
R LOAD
I
R
SOURCE
/f7
781 3-29
Fig. 4.2.6. Three conductor shielded cable allows CT to be remotely grounded while cable shield Is grounded
at both ends.
4.2.7
TM 00361A-12
Section 5
TM 504A Mod WQ
Power Module
TM 09361A-12
F7523A1 Mod WO—TM 504A Mod W®
GG SS OSCILLATOR MOD WO
SGIMCSCIIIATGAMGGWN
*A1018 GISTGGILGN MNLYZN MGGWG
_
____
^o) Q
o
: oOO
^^
v O
o
J
1:1
o 0.)C0)
C)
p
781
Figure 5.1.1. TM 504A Mod WQ Power Module with Plug-Ins.
5.1.0
TM 09361A-12
Part 1 —F7523A1 Mod WQ—TM 504A Mod WQ
SPECIFICATION
transistors for plug-in usage. Rear interface connections allow interconnection of signals between plug ins
INTRODUCTION
Description
Performance Conditions
The TM 504A Mod WQ is a four-wide power module
compatible with all TM 500 plug-ins It provides unregulated dc and ac supplies and non-dedicated power
The values listed below are valid only when the instru
ment is operated at an ambient temperature between
0°C and 50°C.
Table 5.1.1
Electrical Characteristics
Characteristics
Supplemental information
Performance Requirements
SUPPLIES
+ 33.5 Vdc
Tolerance a
+ 23.7 V to + 40.0 V.
PARD (Periodic and
Random Deviation)
.<_ 2 5 V pp.
Maximum load
350 mA.
Maximum load di/dt
10 mA/µs.
-33.5 Vdc
Tolerance a
PARD
-23.7 V to -40.0 V.
2.5 V pp.
Maximum load
350 mA,
Maximum load di/dt
10 mA/µs.
+ 11.5 Vdcb
Tole r ance a
4 7.6 V to + 16.0 V.
PARD
5 2.5 V pp.
Maximum load
Standard
compartment
1.3 A.
High-power
compartment
4.0 A.
Maximum load di/dt
20 mA/µs.
25 Vac (2 each)
Range
25.0 V rms + 10%, -15% floating.
Maximum load
Standard
compartment
25 VA.
High-power
compartment
60 VA.
Maximum floating
voltage
350 V peak.
5.1.1
TM 09361A-12
Specification- F7523A1 Mod WQ—TM 504A Mod WO
Table 5.1.1 (cont)
Supplemental Information
Performance Requirements
Characteristics
SUPPLIES (cont)
17.5 Vacb
Range
With a grounded center tap 20.5 V rrns
+ 10%, -20%.
Maximum load
Standard
compartment
30 VA.
High-power
compartment
95 VA.
Maximum plug-in power
drawn from mainframe
Standard compartment
35 Wdc or 75 VAac.
High-power
compartment
45 Wdc or 125 VAac.
Combined power drawn
sharing limitations
Standard compartment
VAac + 2.1 (Wdc) <75 VAac.
High-power
compartment
VAac + 2.1 (Wdc) < 150 VAac.
Fuse data
+ 33.5 Vdc
2.5 A, 3 AG, fast blow.
-33.5 Vdc
2.5 A, 3 AG, fast blow.
+ 11.5 Vdc
7.5 A, 3 AG, fast blow.
-11.5 Vdc, high power
5 A, 3 AG, slow blow.
SERIES PASS TRANSISTORS
I
Type
I One each NPN or PNP per compartment
Maximum dissipation
Standard compartment
7.5 W each, 15 W total.
High-power
compartment
30 W each, 50W total.
SOURCE POWER REQUIREMENTS
Voltage ranges
Selectable 100 V, 110 V, 120 V, 200 V, 220 V,
and 240 V nominal line ± 10%.
Line frequency
48 Hz to 440 Hz.
Max power consumption
Approximately 320 W.
Fuse data
5.1.2
100 V, 110 V, 120V
ranges
4 A, 3 AG, slow blow.
220 V, 220 V, 240 V
ranges
2 A, 3 AG slow blow.
TM 09361A-12
Specification—F7523A1 Mod WQ—TM 504A Mod WC
Table 5.1.1 (cont)
Performanc e R eq uirements
Characteristics
Supplemental Information
MISCELLANEOUS
Maximum recommended
plug-in power dissipation
One-wide
10to15W.
Two-wide
25 to 35 W.
• Worst case; low line-full load and high line--no load values Including PARD:
b
I
Floating in high-power compartment, 350 V peak.
At nominal line voltage.
11125
18.625
5.375
ri
i
7813-31
Fig 5.1.2. TM 504A Mod WO Outline Drawing.
5.1.3
TM 09361 A-12
Specification—F7523A1 Mod WQ—TM 504A Mod WQ
Table 5.1.2
Physical Characteristics
Supplemental Information
Characteristics Overall
ENVIRONMENTAL
Meets or exceeds MIL-T-288008, Class 5 requirements.
Temperature
Operating
00010 +50°C.
Non-operating
-55°C to +75°C.
Humidity
90-95% RH for 5 days cycled to +50°C.
Altitude
Operating
4.6 km (15,000 ft).
Non-operating
15 km (50,000 ft).
Vibration
0.38 mm (0.015"), 5 Hz to 55 Hz, 75 minutes
Shock
20 g's (1/2 sine), 11 ms, 18 shocks.
Bench handling
45°; 4", or equilibrium, whichever occurs first.
Transportation
Qualified under National Safe Transit Association Preshipment Test
Procedures 1 A-B-1 and 1A-B-2.
MECHANICAL
Net Weight
TM 504A
18.5 lbs (8.4 kg).
Overall dimensions
TM 504A
5.1.4
15.4 in (13.7 cm) H, 11.1 in (28.2 cm) W, 18.6 in (47.2 cm) L.
TM 09361 A-12
Part 2 .-F7523A1 Mod WQ -TM 504A Mod WQ
OPERATING INSTRUCTIONS
GENERAL
power ranges not possible if the power were to be dissipated in the plug-ins themselves.
Installation
Line Voltage Selection/Fuse Replacement
For full installation instructions refer to the procedure at
the end of this section
Power Source
The TM 504A Mod WQ is designed to operate from a
power source with its neutral at or near earth (ground)
potential with a separate safety-earth conductor. It is not
intended for operation from two phases of multi-phase
system.
The line voltage selector, fuse, and power switch are all
part of the line cord plug assembly, located on the rear of
the power module. Verify that the voltage shown in the
selector window is correct for the line voltage available.
If the displayed voltage selection is incorrect (the voltage is indicated by the red-marked window) or the fuses
need replacement, perform, the following procedure.
Refer to Fig. 5.2.1.
Fuse Replacement
Power Usage
With four plug-ins installed, the TM 504A Mod WQ may
require up to 220 watts at the upper limits of high line voltage ranges. Actual power consumption depends on the
particular plug-in configuration and operating modes
selected.
High Power Compartment. Some TM 500 series plugin modules require high power to operate at their maximum capabilities. To meet this requirement the TM 504A
Mod WQ has a high power compartment. When viewed
from the front this compartment is on the extreme right
side of the unit.
1.
Make certain that the power module power switch
(l ocated below the plug-in housing on the front) is
turned off and the line cord is not plugged into the
li ne voltage connector.
2.
To check or replace the main power fuses, press
downward on the tab located on the Line Voltage
Selector just above the power cord receptacle. The
door will open, and the fuses can be inspected or
replaced.
3.
Close the door to reconnect the fuse.
Line Voltage Selection
Loading Considerations. The power capability of the
TM 504A Mod WQ can best be used by carefully planning the plug-in configuration, the external loads, and
the resulting power distributions. Optimum conditions
may be obtained by:
1.
Having equal loads in all compartments.
2.
Dissipating as much power as possible in the external loads.
3.
1.
Assure that the power module power switch is turned
off and the line cord is not plugged into the line voltage connector.
2.
See Figure 5.2.1. Press downward on the tab
located on the Line Voltage Selector just above the
power cord receptacle, this opens the selector door.
3.
Using a small screwdriver, gently pry, first on one
edge, then the other, to remove the line selector
cards. This etched circuit card is approximately 3/4"
square and 1/8" thick.
4.
Note that on each edge of the selector card there is a
red mark, but that the mark is in a different position
on the edge.
Operating the system in an ambient temperature
near 25°C.
Each plug-in is provided access to a pair of heatsinked, series-pass transistors, one NPN and the other
PNP. These transistors enable the plug-in to operate in
5.2.1
TM 09361A-12
Operating Instructions—F7523A1 Mod WO—TM 504A Mod WQ
FUSE
CLIPS
VIEW RED
ON LINE
SELECTOR
PRESS TO
OPEN
LINE SELECTOR
POSITION TO
REVEAL RED IN
/ PROPER SLOT
(Turn Selector
f/
180•for100V)
rT
.
a
s
\
I:III.i
,^
EUROPEAN
FUSE
U.S.
FUSE
Fig. 5.2.1. Llne voltage selection/fuse replacement.
5.
Orient the selector card for the desired voltage
Po wer Modules
range, and press the card into its receptacle.
6.
Ensure that the installed fuse matches the range
selected.
7.
Close the selector door The proper range should
show through the correct window.
8.
It is not necessary that all the plug-in compartments be
utilized in order to operate the Power Module. The only
modules needed are those necessary to complete the
task.
CAUTION
Turn the Power Module off before inserting the
plug-in; otherwise damage may occur to the
plug-in circuitry.
Reconnect the power cord The TM 504A Mod WQ is
ready for use.
Operating Temperatures
Module Installation
The TM 504A Mod WQ can be operated in an ambient air
temperature of 0°C to 50°C. Thermal cutout devices
protect the system by disconnecting the power to the
TM 504A Mod WQ Power Module when internal temperatures rise above a safe operating level. These
devices automatically return power to the unit when the
internal temperatures return to a safe level.
1.
Check the location of the white plastic barrier keys
on the TM 504A Mod WQ interconnecting jack to
ensure that their locations match the slots in the
edge of the plug-in module's circuit board.
2.
Align the plug-in module chassis with the upper and
lower guides of the selected compartment Push the
module in and press firmly to seat the circuit board in
Since the TM 504A Mod WQ can be stored in temperatures between -40°C and + 75°C, allow the instrument's chassis to return to within the operating limits
before applying power.
5.2.2
the interconnecting jack. (Remove the plug-in
module by pulling on the white release latch in the
lower left comer of each module.)
3.
Install the plug-in module retaining bar.
TM 09361A-12
Operating Instructions-F7523A1 Mod WQ-TM 504A Mod WQ
BUILDING A SYSTEM
Plug - In Module Retainer Bar Installation
Family Compatibility
The plug-in module retaining bar is used to ensure that
the installed plug-in modules cannot come out of the
power module while it is being moved or transported.
Note that plug-in modules cannot be removed or
inse rt ed with the retainer bar installed.
Mechanically, the plug-in modules are very similar to
other Tektronix product families. However, they are not
electrically compatible. Therefore, the TM 504A Mod
WQ interface has barriers on the mating connectors
between pins 6 and 7 to ensure that incompatible
modules cannot be inserted. See Fig. 5.2.2. A com-
To install the plug-in module retaining bar, stand the
patible module will have a matching slot between pins 6
power module on its rear-end. Remove the round--head
Phillips screws (holding the top cabinet cover) located
on each side of the TM 504A Mod WQ just behind the
and 7 of its main circuit board edge connector. This slot
and barrier combination is the primary keying
assignment.
front casting. Align the holes on each side of the retainer
bar with the chassis holes, with the plug-in module
retaining bar extending forward and into the module
opening, over the bottom edge of the plug-in module
Reinstall the screws.
Turn - On Procedure
After completing the installation procedure, found at the
end of this section, and installing the plug--ins, turn on
the POWER switch on the TM 504A Mod WQ.
INSTALLATION AND PRE TURN ON
PROCEDURE
Check the rear panel markings_ if the factory settings are
compatible with the available line voltage and frequency, remove the plug-in retaining bar from the
TM 504A Mod WQ and insert the desired plug-ins. Use
the bail to raise the front of the instrument. If a line voltage change is needed, refer a qualified service person
to the procedure in the Maintenance section of this
manual.
SIGNAL SOURCE MEASUREMENT POWER SUPPLY
FAMILY KEY
FAMILY KEY
FAMILY KEY
8A ^o 0 28B
28A co 28B
28A o0 0 28B
28A o 0 28B
o ql
qq
l qq l
qq
l
L^. 24A
o0 24B
23A o 0
qq
00
qq
qq
°oo
° °
ao
oq
00
oo
o0
22A o0 22B
21A o0 21B
o0
oq
00
o°OO
CDI
qq
Iq o
Iq 0
23B
I DOl
I DOl
I DOl
1
7A o 0 7B
6A oo q0 6B
J10
00
00
1A
oo
7A
6A
l
0
]HO 6B
7B
J20
1B
00
00
oq
oq
oq
qo
00
20A oo 208
19A qq
qq
oq
o q 19B
DO
HIGH POWER °oo
00 COMPARTMENTjj
qq
^, )
00
oo
qo
j qq
1 001
DCI
1 00
1B
i
1001
7A
7B
6A p°°6B
q
I DOl
J30
1A
o0
1 001
7A o 0 7B
6A 0 0 6B
Dl
qq
1A qq 1B
I
J40
1A
00
o0 q
^ 1B
TM 500
FAMILY KEY
78
Fig 5.2.2. Keying assignments for family functions. One of many possible sequence combinations.
5.2.3
TM 09361A=12
Section 6
Applications
TM 09361 A-12
Part 1 —F7523A1 Mod WQ
APPLICATIONS
I NTRODUCTION
human subjective perceptions than flat-response
(unweighted) measurements.
The AA 501 A Mod WQ Distortion Analyzer is fast and
easy to operate, yet its features and flexibility make it
ideal for very sophisticated, demanding applications.
This application note explains how to use the AA 501A
Mod WQ and SG 505 Audio Oscillator, plus a number of
other Tektronix instruments, to make the more common
audio-frequency measurements in a variety of
applications.
The AA 501 A Mod WQ Distortion Analyzer has a number
of features to aid level measurements in all three level
modes (VOLTS, dBm, and dB RATIO). It covers a
dynamic range of 156 dB, from a maximum of 199.9 V
( +48.2 dBm) to a guaranteed noise floor of 3 µV
(-108.2 dBm) with the 400-Hz and 80-kHz filters
selected. Typical noise levels are 1.7 µV with the AVG
detector and 2.4 µV using the RMS detector. Defeating
the 80-kHz filters opens the full 300-kHz bandwidth and
typically doubles the noise.
The AA 501 A Mod WQ has a high impedance, fully differential (bridging, fully balanced) input. Impedance from
either side to ground is 100 kfl. Maximum safe input is
300 V peak or 200 V rms. The common-mode rejection
ratio (CMRR) is at least 50 dB at 50 and 60 Hz, typically
holding to at least 40 dB at 300 kHz. By rejecting
common-mode noise picked up on input cabling, this
CMRR permits effective use of the instrument's low input
noise and wide dynamic range in typical applications.
The maximum common-mode voltage at which the
CMRR specifications hold varies as Table 6.1.1 shows.
With no filters selected, the bandwidth of the AA 501A
Mod WQ in LEVEL functions typically extends to 330 kHz
at -3 dB, and 20 Hz to 20 kHz within 0.1 dB. The 400-Hz
highpass, 30-kHz lowpass, and 80-kHz lowpass are
three-pole Butterworth filters with their -3dB points at the
frequency stated and an ultimate rejection slope of 18 dB
per octave (60 dB per decade). The 400-Hz filter thus
typically provides 50 dB or more of rejection of 50- or
60-Hz noise generated in the device under test. The
fourth filter in the AA 501 A Mod WQ is the 'C' MSG filter,
meeting the requirements of IEEE 743-1984. The 'C'
MSG weighting filter is one of a number of filters that
approximate the response sensitivity of the human ear at
different frequencies. Signal-to-noise measurements
made through the 'C' MSG filter will correlate better with
To provide maximum accuracy and correlation to
measurements made with older instruments or methods,
the AA 501 A Mod WQ contains both true-rms and
average-responding, rms-calibrated detectors. When a
relatively pure sinewave signal is being measured, each
detector will give the same result. If significant distortion,
noise, or multiple signals are present, only the true-rms
detector will give an accurate measurement. However,
most audio voltmeters and distortion analyzers have
average-responding, rms-calibrated detectors. When
you need measurements that will correlate with those
made using older instruments, the AVG detector should
be used. For a fuller discussion of true rms versus
average measurements, refer to Tektronix Note
AX-4285, "True Rrns Ac Measurements".
Table 6.1.1
Variation of Common Mode Voltage
with Input Level
INPUT LEVEL VOLTAGE
RANGE
MAXIMUM COMMON
MODE VOLTAGE
200
100
60
30
20
10
6
3
2 (and below)
1
When connecting the device or unit under test to the
AA 501A Mod WQ, be sure to use shielded cable. Connect balanced-output devices with a shielded,
balanced cable (two conductors under shield). The two
high conductors connect to the two input connectors of
the AA 501A Mod WQ. The shield may be either
grounded or floating at either AA 501 A Mod WQ input or
device output, depending on which yields lower noise.
Devices with single-ended outputs are connected by a
shielded cable, with the shield going to one of the
AA 501A Mod WQ balanced inputs and the high
conductor to the other.
Basic Level Measurements
Level, or amplitude, is the fundamental and most common audio measurement. Frequency response, power,
6.1.1
TM 09361A-12
Applications — F7523A1 Mod WO
gain, loss, signal-to-noise ratio, crosstalk, and
separation are examples of level measurements.
Voltage
The VOLTS mode, in LEVEL function, is used to make
level or amplitude measurements when the desired units
are voltage or power. Select the AUTO RANGING
position of the INPUT control and the desired detector
and filter (if any), Then connect to the signal and read the
result from the digital display. LED indicators to the right
of the digits show whether volts, millivolts, or microvolts
are being displayed. You can normally use AUTO
RANGING for all measurements, but if you need to set
the input range manually, rotate the input control until
neither the DECREASE RANGE nor INCREASE RANGE
indicator is lit.
dBm
Another common expression of level in many professional audio applications is dBm, decibels referred to
a power level of one milliwatt in 600 fl. The dBm mode of
the AA 501A Mod WQ is provided for such measurements. Note, however, that the AA 501 A Mod WQ input is
high-impedance (bridging), not 600-f2-terminated.
Thus, dBm readings will be correct only when the
AA 501 A Mod WQ is connected across a 600-fl system
or when the user provides a 600-f2 termination when
making measurements outside a terminated system.
The AA 501 A Mod WQ in dBm mode is not a power meter
but a dB-reading high-impedance voltmeter whose
0-dB reference s 0.775 V.
dB Ratio
The LEVEL mode likely to be most useful is the dB RATIO
mode. This should be used for all relative audio
measurements (frequency response, signal-to-noise,
gain, etc.) and for dB measurements with any reference
other than one milliwatt in 600 f2.
In dB RATIO mode, the user may establish any present
value of signal amplitude as a new 0-dB reference at any
ti me. Simply pressing the "PUSH TO SET 0 dB REFERENCE" button causes the display to go to 0.0 dB, an
internal register to store the signal amplitude, and all
future readings then to be made in dB above or below
that reference until either the button is pressed again or
power is removed from the AA 501 A Mod WQ. Changing
to another mode or function will not change a
previously-stored reference.
6.1.2
Harmonic Distortion (THD+N)
Harmonic distortion measurements are made using the
input and voltmeter sections of the instrument previously
described, plus automatic set-level and automatic
notch-filter circuitry. Harmonic distortion is created by
nonlinearities in a device under test that cause it to generate harmonics (integer multiples) of an applied input
signal. Fig. 6.1.1 shows in frequency-domain representation how a nonlinear device will add harmonic distor
tion to a pure sine-wave input signal. The AA 501A Mod
WQ and other distortion analyzers eliminate the fundamental component with an extremely sharp rejection
filter and then measure the residual components with a
voltmeter. Fig. 6.1 .1 also shows the block diagram of the
analyzer. Since the voltmeter is a wide-band device and
only the fundamental frequency has been notched out,
any broad-band noise or discrete interference such as
ac power-supply ripple from the device under test will
also be measured, Thus, the THD + N (Total Harmonic
Distortion plus Noise) terminology selected by the Institute of High Fidelity (IHF) in 1978, is used to distinguish
distortion analyzer measurements from those made by a
series of individual harmonic-amplitude measurements
with a selective voltmeter, followed by a root-sumsquare calculation. Older distortion analyzers do not
carry the TDH + N terminology but they operate in the
same way. Making harmonic--distortion measurements
with the AA 501 A Mod WQ Distortion Analyzer is simplicity itself. Select input AUTORANGE THD + N function, distortion AUTO, connect the signal, and read the
digital display. The AA 501A Mod WQ will automatically
establish a 100-percent set-level reference on any
input-signal amplitude between 60 mV and 200 V (70 dB
dynamic range), automatically null out any fundamental
frequency between 10 Hz and 100 kHz (four-decade
frequency range), automatically autorange its digital
voltmeter to 100%, 20%, 2%, 01 0.2% full-scale for best
resolution, and digitally display the result. Typical
settling times are 5 seconds or less for a complete
measurement with the maximum 7 seconds required at
low fundamental frequencies and at extremely low
distortion levels. You can alternately display distortion in
dB below fundamental, instead of percentage, by
selecting the dB button below the 0.2% button.
This full automation does not require any "cooperative"
signal source, unlike semi-automatic analyzers that
incorporate the oscillator into the same unit and use the
oscillator to pretune the analyzer. Thus, the AA 501A
Mod WQ provides fully automatic hands-off measurements regardless of whether the test signal comes from
a local SG 505 Audio Oscillator, the user's previous or
experimental oscillator, a network or satellite feed, or a
previously recorded test tape or disc.
TM 09361A-12
Applications—F7523A1 Mod WQ
Fundamental
LHarmonic
A
Fundamental
A
f
Harmonics
F
A
undamental
removed)
F
---------^ -------I
^
AUDIO
OSCILLATOR
-
DEVICE
UTESTR
11
NOTCH
FILTER
AC
VOLTMETER
THD ANALYZER
7813-sal
Fig, 6.1.1. Harmonic distortion added by device under test Is measured with THD analyzer.
For real accuracy in THD + N measurements the truerms detector should always be used since the signal
after the notch filter typically consists of several
harmonics plus broad-band noise. The averageresponding, rms-calibrated detector typically shows
readings 1 to 2 dB lower; its use is required when it is
necessary to correlate measurements to specifications
based on the use of earlier instruments with averageresponding detectors.
You can improve accuracy at low device-distortion
levels by properly selecting filters since the broadband
noise component often then becomes the limiting item.
The 80-kHz low-pass filter is typically used when the
fundamental frequency is 20 kHz or below, since it will
30-kHz filter further reduces noise, in many cases
producing AVG-detector typical residual levels below
0.001 %.
intermodulation Disto rt ion
Another way to measure the effects of device non
li nearity is to use intermodulation distortion (IMD)
testing. In such testing, two or more discrete test tones
are applied simultaneously to the device input and the
products resulting from the mixing action of non-
li nearities are measured. Several popular techniques
exist. The F7523A1 Mod WQ test system automatically
provides this capability through the Twin-Tone function,
still pass second, third, and fourth harmonics while significantly reducing the effect of wide-band noise.
Similarly, you can safely select the 30-kHz filter when the
SMPTE and DIN
fundamental frequency is below approximately 7 kHz.
The 400-Hz high-pass filter will help reject the
distortion-masking effect of power-line-related hum
due to inadequate shielding or power-supply filtering in
the device under test, but it should not be used with
fundamental frequencies below about 500 Hz.
The Society of Motion Picture and Television Engineers
While the AA 501A Mod WQ will automatically make
standard, the tones are 60 Hz and 7 kHz. The DIN stan-
THD + N measurements on any signal amplitude above
60 mV, the results may be limited (depending on devicedistortion levels) by internal noise in the AA 501A Mod
WQ unless the signal amplitude is at least 250 mV (see
Fig. 6.1,2). Above 250 mV, with fundamental frequencies
between 20 Hz and 20 kHz, and with the 80-kHz filter
dard permits a number of harmonically related pair
choices, 250 Hz and 8 kHz being the most common.
Device nonlinearities will produce low-frequency
selected, typical residual distortion and noise levels of a
complete SG 505-AA 501A system are 0.0012% to
0.0016% with AVG detector, and 0.0015% to 0.0022%
with true-rms detector (see Fig. 6.1.3). Selecting the
(SMPTE) and the Deutsches Institut fur Normalizung
(DIN) have promulgated two similar intermodulation distortion standards. Both (see Fig. 6.1.4) use a two-tone
test signal comprised of a low-frequency tone four times
the amplitude of a high-frequency tone. In the SMPTE
modulation sidebands around the high-frequency
signal, as shown in the figure. Fig. 6.1.4 also shows the
simplified block diagram of the AA 501A Mod WQ when
measuring SMPTE, DIN, or Twin-Tone IMD. A high-pass
filter eliminates the low-frequency tone, an am
demodulator recovers the side-bands, and a calibrated
voltmeter measures their amplitude.
6.1.3
TM 09361A-12
Applications—F7523A1 Mod WQ
.D050 RMS
0040 AVG
0028 RMS
.0022 AVG
-
-- ---------
-----__...__-- -__-_---_
60
mV
.0020 RMS
.0018 RMS
.0016 AVG
-------_--.0014 AVG
500
mV
250
120
Input Signal Level
7813-35
Fig. 6.1.2. Typical noise limitation to THD + N reading (with 80-kHz filter selected).
-80 d BB
0010
RMS I RESPONSE (0.0032% GUARANTEED)
AVG RESPONSE (0.0025>%. GUARANTEED)
-88 dB
0..0040°x °
0.0032 °;0
----
-
-90 dB
-
----- +
0.0025 %
- 92 dN
—
0.0020%
- 94 dB
0.0014
-97 dB
-- inn dB
20
50
100
200
500
1K
2K
5K
10K
20K
Frequency, Hz
7813-36
Fig. 6.1.3. Typical Residual THD+Noise AA 501A/SG 505 System (V input> =250 mV with 80- kHz-Noise-Limiting
Filter).
To perform SMPTE and DIN tests using the F7523A1 Mod
WQ, it is necessary to manually set the test tones and
mix them externally. The SG 505 Mod WQ should always
be used to set the lower frequency tone. For example, to
generate a SMPTE test using 60 Hz and 7 kHz tones, the
following procedure may be used:
Adjust the frequency dial on the SG 505 Mod WR to 7,
and press the X1 K range push button. Connect the output of the SG 505 Mod WR oscillator to the input of the
AA 501 A Mod WQ, and press the LEVEL push button on
the AA 501A Mod WQ. Adjust the SG 505 Mod WR
6.1.4
OUTPUT LEVEL controls for a convenient level, such as
1.00 Volt. Disconnect the SG 505 Mod WR from the
AA 501 A Mod WQ.
Next, adjust the frequency dial on the SG 505 Mod WQ to
6, and press the X1 0 range push button. Connect the output of the SG 505 Mod WQ oscillator to the input of the
AA 501 A Mod WQ, and verify the LEVEL push button on
the AA 501A Mod WQ is still depressed. Adjust the
SG 505 Mod WQ OUTPUT LEVEL controls to exactly four
ti mes the level measured from the SG 505 Mod WR, in
this example, 4.00 Volts. Disconnect the SG 505 Mod
WQ from the AA 501A Mod WQ.
TM 09361 A-12
Applications—F7523A1 Mod WQ
INTERMOD
PRODUCTS
f
HF
(7 kHz SMPTE)
(8 kHz DIN)
LF
(60 Hz SMPTE)
(250 Hz DIN)
FREQUENCY Hz
-
HIGH I
PASS I-+
FILTER
AM
DETECTOR
VOLTMETER
7813-37
Fig. 6.1.4. SMPTE or DIN Intermod test.
Connect a 'T" connector to the input of the device under
test. Connect the output of the SG 505 Mod WR to one
branch of the "T" connector, and the output of the SG 505
Mod WQ to the other branch. Connect the output of the
OUT to the input of the AA 501 A Mod WQ and turn on both
SG 505 oscillators. You are now ready to make SMPTE
I MD distortion tests.
While mixing tones in this manner, be sure both SG 505
test signal generator outputs are in the same mode; that
is, both FLTG/GND switches must be in the same
position. Mismatched push button positions will not
damage the test equipment, but may result in
unexpected or er r oneous test results. Also, the SG 505
Mod WR must be set to the 600 fl position to ensure
proper amplitude mixing of the tones.
When in the Twin-tone Test mode, be sure both SG 505
test signal generator outputs are in the same mode; that
is, both FLTG/GND switches must be in the same
position. Mismatched push button positions will not
damage the test equipment, but may result in
unexpected or erroneous test results.
Operation of the AA 501A Mod WQ in Twin-Tone IMD
testing is as simple as THD testing; select AUTO input,
I MD mode, and AUTO display, then read the result. The
400-Hz filter should not be used; the 80-kHz or 30-kHz
filters will have little effect, since the voltmeter's
measurement bandwidth is already narrow due to lowpass filtering after the am demodulator. Dynamic range
for auto-set level is the same 60-mV to 200-V range as
in THD + N mode.
Twin-Tone
To perform Twin-Tone Intermodulation testing, both the
SG 505 Mod WR and SG 505 Mod WQ must be used, but
manual level setting and external mixing is not
necessary. Push the TWIN-TONE TEST SIG push button
in on the SG 505 Mod WR to automatically activate this
function. In this mode, the SG 505 Mod WR provides the
high frequency tone, and the SG 505 Mod WQ provides
the low frequency tone. The frequencies of the tones are
set by the operator using the respective SG 505 front
panel controls. The tones are automatically mixed as
equal peak-to-peak voltage amplitudes (1:1 ratio), and
are available at the SG 505 Mod WR output.
CCIF Difference Tone (IHF-IM)
The Twin-Tone Test can be used for the CCIF test, shown
schematically in Fig. 6.1.5. Two equal-amplitude closely spaced signals are fed to the device under test. If
asymmetric nonlinearities exist, a second-order difference product will be produced at the low-frequency
signal equal to their spacing. To make this measurement
requires a low-pass filter followed by a voltmeter, as
provided by the AA 501 A Mod WQ. The AA 501 A
Mod WQ will automatically measure the amplitude of the
difference tone.
6.1.5
TM 09361A-12
Applications—F7523A1 Mod WQ
14 kHz
16 fl. When the signal is a clean sinewave, either AVG or
RMS detectors may be used. Filters are not normally
used during power measurements. Often, you may want
to measure power exactly at the clipping point of an
amplifier; the oscilloscope monitoring section of this
note describes an extremely sensitive method to
determine clipping threshold
15 kHz
1 kHz
DIFFERENCE
HF
TONE
TONES
Decibels
FREQUENCY Hz
LOW
^" PASS
FILTER
VOLTMETER
7813-38
Fig. 6.1.5. CCIF Intermod test.
Switching between the two IMD block diagramsSMPTE or DIN on the one hand and CCIF on the other— is
done automatically within the AA 501 A Mod WQ The
instrument compares the amplitudes of the lowfrequency (below 1 kHz) and high-frequency (above 1
kHz) energy in the input signal to decide which type of
test is being made. If the low-frequency amplitude is at
least equal to the high-frequency amplitude, the instrument assumes a SMPTE or DIN test and operates relays
to set up the block diagram of Fig. 6.1.4 It the lowfrequency energy is at least 14 dB below high--frequency
energy, the AA 501A Mod WQ assumes the CCIF standard (with no more than 20% IMD) and operates relays to
set up the Fig. 6.1.5 diagram. If this automatic sensing
and changeover are undesirable for any reason, a threeposition internal jumper can be moved to either the
SMPTE/DIN position or CCIF position instead of the
AUTO position.
Make Common Audio Measurements Easier
While the preceding text covers all the standard, built-in
modes and features of the AA 501 A Mod WQ, the following discussion provides additional insight into how
to perform many commonly made audio measurements
in the fastest and easiest manner.
Power
Audio power measurements are performed by
measuring the voltage across a known load resistor and
calculating power from P = V2/R.
Fig. 6.1 .6 provides quick voltage-power conversions for
the three common loudspeaker impedances of 4, 8, and
6.1.6
One standard reference for decibel measurement is built
into the AA 501A Mod WQ. Selecting dBm provides dB
scaling and a reference (0 dB) value of 0.775 V, which is
1 mW in 600 S2. As noted previously, the AA 501 A Mod
WQ always has a high-impedance (bridging) input and
the user must assure that a 600-fl termination is externally provided for dBm calibration to be correct.
For those who prefer decibels referred to one volt (dBV),
the dBm button can be converted to dBV by connecting a
jumper between pins 8 and 9 on J1600 on the logic
board.
To measure dBV or dB to any other reference value without modifying the instrument, you may use the dB RATIO
mode_ First, determine the voltage corresponding to the
desired reference; table 2 shows a number of common
references. Connect the SG 505 Mod WR or any
variable-amplitude audio oscillator to the AA 501 A Mod
WQ input; select LEVEL and VOLTS mode and adjust the
oscillator amplitude for the desired reference voltage.
Then select dB RATIO mode and press the PUSH TO SET
0 dB REFERENCE button. The dB RATIO mode will now
be calibrated to read dB with respect to the new
reference until either the power is removed from the
AA 501A Mod WQ or the PUSH TO SET .. button is
pressed again.
Gain and Loss
Two different philosophies exist for measuring gain:
voltage gain and transducer gain.
Voltage gain is the ratio of signal voltage at the output to
the signal voltage at the input of a device. To measure
voltage gain, connect the output of the SG 505 Mod WR
to the input of the AA 501A Mod WQ. Select the LEVEL
mode on the AA 501A Mod WQ and adjust the SG 505
Mod WR to the recommended level compatible with the
input of the DUT. Next, select the dB mode on the
AA 501A Mod WQ, and push the PUSH TO SET 0 dB
push button. Now connect the output of the DUT to the
input of the AA 501 A Mod WQ. The AA 501 A Mod WQ will
now directly display the DUT voltage gain or loss in dB.
TM 09361A-12
Applications—F7523A1 Mod WQ
H
27
EEE
50O W
300
200
100
70
50W
17_
30
20
g^
I
t6
dBW
^
10
Sw Power
( Watts)
-7 -
3
1
^C^
i
7
3
2
_
010
.2
.3
.5
_
ri
50mW
—_.
2
3
5
7
10V
20
30
50
70
100V
Voltage Across Load Resistance
7813-39
Fig. 6.1.6. Voltage across load versus power (wa tt s or dBW).
Table 6.1.2
0 dB Reference Voltages
Reference Level
Voltage of 0 dB
Reference
1 volt (dBV)
1.000 V
1 mWin600fl
0.775V
6 mW in 600 fl
1.897 V
1 mWin150fl
0.387V
6mWin150Si,
0.949 V
1 mW in 50 S).
0.224 V
6mW in50fl
0.548V
Transducer gain is the ratio of power delivered to a
specific load impedance, to power available from a
source of specific impedance. As in a voltage gain
measurement, adjust the SG 505 Mod WR oscillator for
the frequency and device output amplitude desired.
Disconnect the oscillator output from the device input,
terminate the oscillator with a precise 600-fl load, and
connect it to the AA 501 A Mod WQ input, Select dB
RATIO and press the PUSH TO SET ... button. Remove
the termination and reconnect the oscillator to the device
input. Connect the device output (terminated in 600 fl) to
the AA 501 A Mod WQ input. The AA 501 A now displays
transducer gain. The oscillator frequency can be
changed to any other frequency and transducer gain
measured directly, since the SG 505 Mod WR flatness is
within 0.1 dB.
Note that the transducer gain technique and voltage gain
technique will give identical measurements if the device
input is truly a 600-52 resistance.
Frequency Response
No filters should be selected during a frequencyresponse measurement of an external device. To
measure frequency response on a transducer response
basis, set the SG 505 Mod WR to 1 kHz or other
6.1.7
Applications-F7523A1 Mod WQ
appropriate midband reference frequency. Connect the
SG 505 Mod WR output to the device input and the
device output to the AA 501 A Mod WQ. In one of the two
absolute LEVEL modes, VOLTS or dBM, adjust the
SG 505 Mod WR amplitude and/or device gain controls
to obtain the output level from the device at which
response is to be measured. Select dB RATIO mode and
press the PUSH TO SET 0 dB REFERENCE button. The
SG 505 Mod WR can now be changed to any desired
frequency and frequency response can be read directly
from the AA 501 A Mod WO. The 'Spectrum Analyzer
Driven From AA 501A Mod WQ INPUT MONITOR Connector' section, described later in this application,
explains the technique for a swept, stored frequency
response measurement.
The AA 501 A Mod WQ and SG 505 Mod WR flatness (as
a system) is typically 0.1 dB from 20 Hz to 20 kHz.
For frequency response measurements on the voltage
basis (zero source impedance) the SG 505 Mod WR
amplitude must be readjusted when necessary to
provide a constant input voltage across the device
terminals.
Both the voltage technique and the transducer technique
of measuring frequency response will produce exactly
the same relative response if the device input is purely
resistive, or if any shunt reactive component remains
approximately two or more orders of magnitude above
the oscillator output impedance across the frequency
range.
TM 09361A-12
rather than output noise. This is done by making an
absolute-output-noise measurement, a voltage gain
measurement, and dividing the output-noise voltage by
the device-voltage gain.
Harmonic Distortion Versus Frequency
When characterizing a device or system, it is common to
measure distortion at a number of spot frequencies
across the band, all at a constant output voltage or
power level from the unit under test. Use the following
procedure to make such measurements. Set the SG 505
Mod WR frequency to a midband reference such as
1 kHz, Then adjust its amplitude to provide the desired
device reference output across a specified load, using
the AA 501 A Mod WQ in LEVEL and as appropriate, in
either VOLTS or dBm mode. Select dB RATIO and press
the PUSH TO SET ... button. Select THD + N and read the
distortion, Now, select each new frequency desired for a
distortion measurement. At each frequency, select dB
RATIO mode and, if necessary, adjust the SG 505 Mod
WR output amplitude for a 0.0 dB reading (no adjustment
will be necessary if the device has a flat frequency
response). Then, select THD + N and read distortion.
Some power amplifiers and am transmitters will not withstand continuous sine-wave power output at or near
their maximum ratings. In such a case, either the SG 505
Mod WR output OFF-ON switch or step attenuator may
be used to eliminate or reduce signal levels and permit
cooling of the device between short tests, yet allow a
quick return to the desired test level for a quick THD + N
test.
Signal-To-Noise Ratio (S/N)
Signal-to-noise measurements are extremely simple
using the dB RATIO mode and autoranging feature of the
AA 501 A Mod WQ with the SG 505 Mod WR output OFFON switch. Adjust the SG 505 frequency and amplitude
to provide the device output desired as the S/N reference. Select dB RATIO mode; press the PUSH TO SET
... button, and then press the SG 505 Mod WR OFF
button. This disconnects the oscillator and backterminates the SG 505 Mod WR output connector with a
600-fl resistor. The AA 501A Mod WQ will directly
display the device S/N ratio. If an 'C' MSG or low-passfiltered measurement is preferred select the appropriate
filter and read the display. Any other desired psophometric filter could be provided via the external-filter
capability. For more information, see the section on
user-supplied external filters.
If absolute noise measurements are required instead of
S/N ratio, use the VOLTS or dBm modes and the SG 505
Mod WR OFF button. It is sometimes necessary to
express noise in terms of equivalent device-input noise
6.1.8
Continuously swept distortion tests are not practical with
the AA 501 A Mod WQ, since it tunes in frequency bands
and requires several seconds to settle after each automatic band switching.
Distortion Versus Power or Voltage
Another common way to characterize a device is by a
series of distortion measurements at a single frequency
(usually midband), but across the entire dynamic range
of the device. This technique is particularly important
when you are looking for amplifier-crossover distortion
or other problems occurring at low levels rather than at a
device's maximum output.
At the selected frequency, drive the device to maximum
rated out-put across the specified load, measuring with
the AA 501A Mod WQ in LEVEL and in either VOLTS or
dBm mode. Select dB RATIO, press the PUSH TO SET ...
button, select THD+N, and measure the distortion.
Select dB RATIO again and reduce the SG 505 Mod WR
output until the next lower level at which distortion is to be
TM 09361A-12
Applications—F7523A1 Mod WQ
modulation monitor are at the same site, the connection
shown in Fig. 6.1.7 is used. Defeat or bypass any nonli near audio processing equipment in the chain. Connect
the SG 505 Mod WR output to the principal microphone
input jack, and connect the modulation monitor output to
the AA 501 A Mod WQ input (see Fig. 6.1.7). After adjusting microphone gain controls and SG 505 output amplitude for approximately 25% modulation with the
AA 501 A Mod WQ in THD + N mode, determine whether
the GND or FLOATING connection of the SG 505 Mod
WR results in the lowest distortion and noise product.
Use whichever is lowest.
measured is indicated in dB. For example, if readings
are to be made at maximum power and then at 2:1 power
reductions below that, readings will be taken at -3.0 dB,
-6.0 dB, -9.0 dB, etc. As each new level is established,
select THD + N and read the distortion. Since distortion
typically increases rapidly near maximum power, it may
be desired to make several t dB reductions first and then
go to larger steps. If only a few quick measurements
across a wide dynamic range are needed, the step
attenuator of the SG 505 Mod WR permits 10 dB
changes without use of the variable control. The lower
li mit of dynamic range is set by the AA 501A Mod WQ
60-mV minimum requirement for set level corresponding
At midband (usually 1 kHz), adjust the SG 505 Mod WR
amplitude until the modulation monitor indicates exactly
100%. Select LEVEL and dB RATIO; press the PUSH TO
SET ... button, select THD + N and record the distortion
value. Record a 0.0 dB value for relative frequency
response. At the same frequency, reduce the oscillator
amplitude to obtain the next lower required modulation
percentage (usually 85%) on the monitor. Select LEVEL
and record the dB reading; select THD + N and record
the distortion reading. A complete run normally consists
of oscillator level and THD + N readings at four modu-lation percentages (usually 100%, 85%, 50%, and 25%)
and at a number of frequencies across the audio band.
to power levels of 0.9 mW, 0.45 mW, and 0.225 mW
respectively across 4-, 8-, and 16-dl loads.
Disto rt ion and Response Versus Frequency
At Constant Modulation Percentage
In the broadcasting industry, regular proof-of-
pe rf ormance tests are required to assure that adequate
audio quality is being delivered to listeners. Each station
normally has an accurate modulation monitor that not
only measures percent modulation, but delivers a lowdistortion (and de-emphasized, in the case of
frequency-modulation broadcasting) output for connection to a Distortion Analyzer such as the AA 501A
Mod WQ.
Distortion graphs may be plotted directly from the data.
Frequency response graphs require all algebraic signs
to be interchanged on the level readings (plus/minus,
minus/plus), since a fall-off in station frequency
response requires an increase in oscillator level to
obtain a constant modulation percentage.
Two slightly different procedures are used, depending
on whether the studio and modulation monitor are at the
same location (within convenient audio-cable run
distances) or at separate sites. Where studio and
AA501
o ^
O
SG505
o
O
qo qq
INPUT q
qqqq
000
O
o
SC5021314
O
O
00 0
O
OO
OUTPUT
CONSOLE
MIS
LINE
AMPLIFIER (S)
AM
LIMITERS
(ACTION
DISABLED)
MODULATION
MONITOR
TRANSMITTER
7813-40
Fig. 6.1.7. Interconnection diagram for disto rt ion and response vs frequency measurements.
6.1.9
TM 09361A-12
Applications—F7523A1 Mod WQ
continuously bridged across the SG 505 Mod WR out
put. The other uses a second AA 501 A Mod WQ in LEVEL
and dB RATIO modes as the level indicator. A frequency
counter fed from the SG 505 Mod WR SYNC OUT is
A separated studio and transmitter set-up requires two
test-equipment packages: an oscillator, a level meter,
and (possibly) a frequency counter at the studio, and the
AA 501A Mod WQ Analyzer at the transmitter site.
Fig. 6.1 .8 shows two variations on the "send" package
at the studio One uses a DM 502A auto-ranging, dB-
convenient in either case if a relatively unskilled helper is
assisting with the proof-of-performance at the studio
reading multimeter as a digital-readout level meter
end.
SYNC
OUT
(0
qO
q
o q
DO
0
®O p
^0 q O O
SG505
dB2A
OSCILLATOR
METER
4
DC50X
COUNTER
1.I
^
ee^
NE
AMP
CONSOLE
MIC
LINE
TO
XMTR
SYNC
OUT
l.J
0
00
DO
00
0000
Q
o
o
O o
SG505
OSC.
00
00
0
O
0
BEVEL,
LEVEL,
dB RATIO
COUNTER
LINE
CONSOLE
MIC
LINE
AMP
TO
XMTR
7813-41
Fig. 6.1.8. Two variations of the "send" package.
6.1.10
TM 09361A-12
Applications—F7523A1 Mod WQ
In either case, the engineer at the transmitter controls the
test. He or she need never touch the AA 501 A Mod WQ
(which has been connected as before to the
modulation-monitor output); the AA 501A Mod WQ
remains in THD+N mode at all times. The transmitter
engineer requests each test frequency from the studio
operator. If this operator is only semi-skilled, the
frequency counter's digital display is a powerful
advantage and virtually eliminates frequency-setting
errors. Over the intercommunication facility, the transmitter engineer requests upward or downward
oscillator-level adjustments until the desired modulation percentage is achieved. The transmitter engineer
then records the THD + N reading and asks the studio
operator to provide the digital display of amplitude, in
dB. If the DM 502A is being used, this will be an absolute
reading in dBm or dBV. If a second AA 501 A Mod WQ is
available for studio use, it can be used in LEVEL and dB
RATIO mode and normalized at midband via the PUSH
TO SET button. This normalization is particularly convenient in fm proofs, where transmitter pre-emphasis
causes the required oscillator level to vary over a wide
dynamic range. The mid-band normalized dB readings
can be immediately compared to the permissible limits
without arithmetic computations.
The procedures described in the preceding paragraphs
use the voltage method of determining frequency
response. The voltage method and transducer method
normally produce identical results when measuring
broadcast system frequency response, since broadcast console microphone inputs typically approximate a
pure resistance within the audio band. If, however, you
wish to measure response on a transducer basis, a calibrated constant-impedance step attenuator (gain set)
must be inserted at the oscillator output. The oscillator
measurements even at low frequencies due to its dual--register architecture.
Determining Amplitude for a Specific
Disto rt ion Percentage
Certain applications, particularly those involving
measurements of magnetic-tape recorders, require
determining a reference amplitude level. This level is
defined as the amplitude that produces X% distortion.
The auto-set-level capability of the AA 501A Mod WQ
adds particular speed to this measurement.
Select THD + N mode and adjust the signal amplitude
until you observe the desired distortion percentage, frequently 3% in tape systems. Since a digital display is not
optimum for analog adjustments, you may wish to cali
brate the 10-segment LED indicator if you frequently
make these measurements To do this calibrating, carefully adjust the level until the desired distortion
percentage is obtained. Lock out the percent-distortion
autoranging feature by selecting the lowest range button
that does not produce an over-range indication. Note
how r^ zany segments of the LED "bar-graph" are lighted,
and the degree of variable intensity of the uppermost
li ghted one. Now you can quickly adjust levels to
approximate this "bar-graph" display in future tests,
observing the digital display for fine tuning.
SINAD
As specified in EIA Standard RS 204A, July 1972, the
SINAD test is a standard specification for sensitivity of
two-way mobile fm receivers SINAD stands for the
following ratio:
amplitude will then be left fixed, and the attenuator (gain
set) controls manipulated to obtain the desired modulation percentage. Operationally, the voltage method is
more convenient when semi-skilled helpers are
involved. They can read amplitude directly with 0.1 dB
resolution from either the DM 502A or AA 501 A Mod WQ
with much less chance of error than when using a complex step attenuator.
Several Tektronix TM 500 frequency counters are
suitable for this application. The DC 504 is the lowestpriced, and its 5-digit display is adequate for the application; 1-Hz resolution (1 second gate time) should be
selected. The DC 508/A offers more digits and an audiofrequency resolution multiplier providing 1-Hz resolution
in a 0.01-second gate time. While considerably more
expensive. The DC 508A also makes rf measurements
through VHF and UHF frequencies. The DC 509 should
also be considered for its ability to make high-resolution
Signal + Noise + Disto rt ion
Noise + Distortion
The test is performed with a frequency-modulated cali-
brated rf-signal generator and a distortion analyzer as
shown in Fig. 6.1.9. The rf generator is modulated at twothirds the rated peak deviation for the receiver being
tested. The automatic-nulling and auto-set-level
features of the AA 501 A Mod WQ Distortion Analyzer
greatly speed SINAD testing compared to what can be
done with earlier analyzers. The AA 501A Mod WQ is
placed in THD + N mode, and dB readout of distortion is
selected. The AA 501 A Mod WQ input is driven from the
speaker-output terminals (across a resistive load) of the
receiver. Start from a moderately higher rf-signal level
that produces at least a -20 dB SINAD reading. Then
reduce the generator rf output until the AA 501 A Mod WO
indicates -12dB. At this point, the generator output is
6.1.11
TM 09361A-12
Applications-F7523A1 Mod WQ
equal to the 12-dB SINAD sensitivity of the receiver.
Note that the audio signal being measured by the
AA 501A Mod WQ at this point is definite nonsinusoidal,
consisting of large amounts of noise. Thus, theoretically,
the true--RMS detector in the AA 501A Mod WQ should
be used for accuracy. However, when the SINAD technique was developed and rated sensitivities for fmmobile receivers were established, all distortion
analyzers had only average-responding, rmscalibrated detectors. Therefore, to obtain correlation
with existing sensitivity specifications, you must use the
AA 501 A Mod WQ AVG detector for SINAD tests.
Observation of the analog bargraph indicator may be
useful to get close to the 12dB SINAD value, with the
digital display then observed for the final adjustments.
Intermodulation Distortion at Nonstandard
Frequencies
Users may wish to use a high--frequency tone lower than
the 7 kHz of SMPTE or 8 kHz of DIN when measuring
low-bandwidth equipment. For example, a voice-grade
communications link or recorder with cutoff above 3 or
3.5 kHz could not be tested for IMD with the 7-kHz tone,
but could be by bringing the upper tone within its
passband.
Higher-than-standard upper-frequency tones are used
principally in determining the transient-intermodulation
susceptibility or slew-rate problems of a wide-band,
high-quality audio amplifier. The advantages of a
SMPTE--like IMD test with upper-frequency tones
between 15 kHz and 100 kHz are discussed in depth in a
technical paper, "A Comparison of Nonlinear-Distortion
Measurement Methods".'
These tests are far simpler to perform than other
suggested dynamic-intermodulation (DIM) or transient-intermodulation (TIM) tests and can be done fully automatically by the F7523A1 Mod WQ test system.
Filters-Internal and External
The ac voltmeter section of the AA 501 A Mod WQ
Analyzer, that ultimately performs all the analyzer's
measurements, is a wideband unit typically down 3 dB at
330 kHz. In many measurement applications this full
bandwidth is unnecessary or even undesirable. Furthermore, some particular applications call for very specific
control of bandwidth, perhaps passing or rejecting only
narrow frequency bands. Consequently, the AA 501 A
Mod WQ was designed with four commonly used filters
as standard, and with convenient external connections
for any other desired filters.
Built-In Filters
Figures 6.1 .10 through 6.1.13 show the typical frequency
responses of the four built-in filters of the AA 501A Mod
WQ. The 400-Hz high-pass filter (Fig. 6.1.10) is used to
reduce the effect on distortion or noise measurements
due to power-supply hum in the unit under test. It should
not be used for distortion measurements at fundamental
frequencies below approximately 500 Hz.
1 Richard C. Cabot, Audio Engineering Society paper
No. 1638, May 1980.
CALIBRATED
FM
SIGNAL
GENERATOR
ANT.
IN
0
0
0
0
°o °
2-WAY MOBILE
RECEIVER
00
0
SPKR.
OUT
°
0
00
°o o°
00
OOO
AA501
THD+N
dB DISPLAY
7813--42
Fig. 6.1.9. SINAD measurement setup.
6.1.12
TM 09361A-12
Applications—F7523A1 Mod WO
5
0 dB
10
- i5
20
i
30
35
-
40
45
I
_
25
^^
50
4
^
I
_^
r
fi —
-
55
60
I
^
- 65
70
10 Hz 20 30 50 100 Hz 200 300 500 1 kHz
i
2
5
10 kHz 20 30 50 100 kHz 200 300
7813-43
Fig. 6.1,10. Frequency response cu rve for 400 Hz high-pass filter.
-5
0 dB
10
15
20
25
30
35
40
45
50
!
jI
iIk
THE
0
v
^
s
N
55
60
65
70
10 Hz
20
30
50
100 Hz
200 300
500
1 kHz
2
EEEEE
5
10 kHz
20 30
50
100 kHz 200 300
1813-44
Fig. 6.1.11. Frequency response curve for 80 kHz low-pass filter
The 80 kHz and 30 kHz filters (Figures 6.1.11 and 6.1.12)
reduce the noise contributions to permit measurement of
lower distortion levels. Of course, they also reduce
harmonic-distortion products and are not normally used
when measuring distortion at fundamental frequencies
above one-fourth to one-third their cutoff frequencies.
The US Federal Communications Commission permits
use of the 30 kHz filter during broadcast-station proofof-performance tests.
'C' MSG (Fig. 6.1.13), normally used only during noise
measurements, provides better correlation to human
perceptions of noise levels because its low- and highfrequency roll-off approximates the frequency response
of the human ear.
6.1.13
TM 09361A-12
Applications—F7523A1 Mod WO
>5
0 dB
10
is
^o l
f
25
-
~
v
3o
a
35
90 —
A5
50
55
-60
- 65
- 70
10 Hr 20 30 50 100 Hz 200 300 500 1 kHz
2
5 10 kHz 20 30 50 100 kHz 200 300
7813-45
Fig. 6.1.12. Frequency response cu rv e for 30 kHz
+15
+10
+5
0 dB
-5
-10
-15
-20
-25
-30
-35
-40
-45
-50
-55
-60
20
10 Hz
low . -p;-iss
filter.
_
I_
iiiIIIii
C
ess
IZi
e
_
—
I
iiiiiii
30
50
200 300
100 Hz
500
2
1 kHz
5
20 30
50
10 kHz
7813-46
Fig. 6.1.13. Frequency response curve for the 'C' MSG weighted filter.
The °C MSG, 400-Hz, and 80-or30--kHz filters are independent, additive, and may be used in any combination.
Modifying a 30-kHz filter to the 22.4-kHz IEC
Standard
H wever, the 80-and 30-kHz filters share components;
if both are selected, only the 30-kHz response is in
effect.
You can convert the 30-kHz filter to a 22.4-kHz cutoff
as specified in IEC standard 268 and CCIR
6.1.14
TM 09361A-12
Applications-F7523A1 Mod WQ
recommendation 468-2 by replacing three resistors.
Change R1110, R1112, and 81210 to 21.0 kfl. Partslocation information is provided in the F7523A1 Mod WQ
Service Manual.
User -Supplied External Filters
There are many specific applications where it is
desirable to employ one or more specific filters such as.
- a 19-kHz reject (notch) filter to prevent the stereopilot carrier from masking distortion or noise
measurements of fm tuners and receivers.
- multiple-pole 300-Hz high-pass to reject continuous tone squelch-signaling (CTSS) tones when
making measurements in two-way mobile radio
systems.
- narrow band-pass filters to permit measurement of
second harmonic only or third harmonic only, rather
than total harmonic distortion. Such measurements
are common in magnetic-tape system measurements.
- psophometric filters other than 'C' MSG
- Dolby CCIR.
- low-pass or notch filters, as appropriate, to reject
remote-control signaling tones used in some
broadcasting networks with unattended remote
transmitters.
- a notch filter to reject a tone used to hold companders in an audio transmission line at some
reference gain level while making absolute noise
measurements.
External filters can be conveniently connected either via
AA 501A Mod WQ front-panel jacks or rear-interface
connections. FUNCTION OUTPUT (front panel, or pins
23B high and 24B ground at the rear) drives the filter
input. The filter output connects to AUXILIARY INPUT
(front, or pin 25B high and pin 26B ground at rear). Both
are single-ended, ground-reference signals. Source
i mpedance at FUNCTION OUTPUT is 1 kfl; input
i mpedance at AUXILIARY INPUT is 100 kfl and ac
coupled. The filter must be unity (X1) gain in its passband, and capable of passing 2-volt rms signals without
clipping or compression.
User-Built Filters
Commercial, lab-grade filters with the appropriate
characteristics may be used with the AA 501 A Mod WQ,
but most users will find it more convenient and less
expensive to build their own in TM 500 custom plug-in
kits, using modern active-filter technology. These kits
are available in three versions. The single-width kit without power-supply components is Tektronix P/N
040-0652-05; a single-width kit including parts to build
regulated plus-and-minus supplies on the rear part of
the board is Tektronix P/N 040-0803-02; and a double-width kit without power-supply components is Tektronix
P/N 040-0754-07. Each consists of the mechanical
structure (in knocked-down form) of a TM 500 plug-in.
The circuit board (or two boards in the 040-0754-07) is
perforated on 0.100-inch centers for convenient construction of custom circuits with integrated circuits and/
or discrete components.
Custom kits include information on interfacing with the
TM 500 mainframe's unregulated power supplies More
detailed information is available in Tektronix Application
Note number AX-3303-2, Suggested Power-Supply
Circuits for the TM 500 Blank Plug-in Kit. Switches and
connectors can be easily mounted on the kit's front
panel section. The completed filter project plugs into any
TM 500 mainframe.
Using the INPUT MONITOR and FUNCTION
OUT Connections
INPUT MONITOR provides a buffered, constantamplitude version of the AA 501 A Mod WQ input signal.
Output impedance is 1 kfl, ground referenced; rearinterface pins are 24A high and 23A ground. Amplitude
will be a constant one-volt mis with input signals
between 60 mV and 200 V. Below the agc and autoset-level threshold at approximately 60 mV, the INPUT
MONITOR output signal will decrease with a constant
gain of approximately 26 dB (X20) above the INPUT
connector.
FUNCTION OUT provides the ac signal following all
processing and filtering, just prior to feeding the
1.999-volt full-scale ac voltmeter that comprises the
final section of the AA 501A Mod WQ. This signal thus
comes after the notch filter in THD + N mode, after the
filters and demodulator in IMD mode, and after the four
built-in filters in all modes. Source impedance is 1 kfl,
single-ended; rear-interface terminals are 23B high and
24B ground. Since this signal is effectively at the input to
a 1.999-volt full-scale voltmeter, the calibration is
always one millivolt rms output per count in the digital
display (except in dB-display modes). For example, at a
displayed voltage of 1.456 mV, the output will be 1,456 V;
a displayed THD+N reading of 0.0083% will provide
83 mV at this jack. Decibel conversion in the AA 501A
Mod WQ follows the detector and thus does not affect
the FUNCTION OUTPUT signal.
6.1.15
Applications—F7523A1 Mod WQ
Oscilloscope Monitoring
Useful information on the content of the signal being
measured by the AA 501 A Mod WQ Analyzer can be
obtained by observing the FUNCTION OUTPUT signal
on an oscilloscope. Interpretation and stable oscilloscope triggering are aided by also observing the INPUT
MONITOR signal on a dual-trace oscilloscope and triggering from the channel displaying INPUT MONITOR.
The FUNCTION OUTPUT trace can then show whether
the predominant signals are broadband noise, individual harmonics or a combination of harmonics, or
power- line-related hum. Power-line-related hum is
most easily detected by placing the oscilloscope time
base on 2 ms per division and selecting LINE triggering;
50- or 60-Hz line-related noise will then be stable while
actual distortion products will run through the display.
The dual-trace scope, triggered from the INPUT
MONITOR channel and with the time base adjusted to
display one to two cycles on the INPUT MONITOR trace,
also becomes an extremely sensitive indicator of the
clipping threshold of the device under test.
Such a setup makes it easy to detect clipping even when
the products are below 0.01 % (-80 dB), long before any
flattening can be visually observed on the device's output waveform.
Some users prefer to use a monitoring oscilloscope as
an X-Y monitor rather than in conventional time-domain
fashion. With the INPUT MONITOR and FUNCTION
OUTPUTS as the two signals, Lissajous patterns result,
from which a trained observer can determine harmonicorder content.
Spectrum Analyzers and the AA 501 A
Mod WQ
Spectrum analyzers and total-harmonic-distortion
analyzers are often considered as alternative, even
competing, approaches to obtaining quantitative information about the distortion produced by a device.
The total-harmonic-distortion analyzer produces a
single reading that lumps together the effects of all
harmonics, wide-band noise, and any interfering
signals such as power-supply hum. A THD analyzer is
simpler to operate and interpret (particularly a totally
automatic digital-read-out instrument like the AA 501A
Mod WQ) than a spectrum analyzer. Although ultimately
li mited by noise since they are wide-band instruments,
state-of-the-art analyzers like the AA 501 A Mod WQ
are capable of readings approaching 100 dB below
fundamental (average-responding detector).
The spectrum analyzer, however, provides more information than a THD analyzer. It shows the amplitude of
6.1.16
TM 09361A-12
each individual spectral line—fundamental and
harmonic. It can also show interfering signals like
power-supply hum as discrete spectral lines. However,
it requires higher skill to use and interpret than a THD
analyzer. Furthermore, if a single % THD number is
required, a user with only a spectrum analyzer must
perform a root-sum-square computation upon the
amplitudes of the individual harmonics. The scanning
spectrum analyzer can be a very narrow-band device,
depending on choice of resolution bandwidth, and so is
theoretically less noise-limited than the wide-band THD
analyzer. However, current state-of-the-art spectrum
analyzers are limited to approximately 80- to 90-dB
dynamic range and thus cannot match the -90-- to
-100-dB residual floor of the AA 501 A Mod WQ.
An audio spectrum analyzer such as the Tektronix 7L5 or
5L4N can be connected with the AA 501 A Mod WQ
Distortion Analyzer to synergistically obtain greater
measurement power than either instrument provides
alone. Two connections are possible; each has different
applications and different benefits.
Spectrum Analyzer Driven From AA 501A
Mod WO FUNCTION OUTPUT Connector
The primary advantage of this setup (see Fig. 6.1.14) is
that it extends dynamic range, permitting measurements
significantly below what either AA 501 A Mod WQ or
spectrum analyzer could do alone. Such measurements
are possible because the AA 501A Mod WQ eliminates
the fundamental signal as a limiting item on spectrumanalyzer dynamic range, and the narrow resolution
bandwidths possible in the spectrum analyzer reduce
the basic-noise-floor limitation of the wide-band
AA 501 A Mod WQ. This dual analyzer configuration also
converts a single-ended spectrum analyzer to a highCMRR differential input as far as the signal is concerned.
Furthermore, the autoranging circuitry of the AA 501A
Mod WQ prior to FUNCTION OUTPUT makes it
unnecessary ever to reset the spectrum analyzer's
amplitude controls after an initial setup. The spectrum
analyzer can do its usual job of individual distortionproduct analysis, but now at levels it could not touch if
fed directly from the signal.
Amplitude setup and scaling to the signal are simple.
The spectrum analyzer will normally be set for a one-volt
(0 dBV) reference level; one exception will be noted
below. As noted earlier, the scaling of the FUNCTION
OUTPUT jack is one millivolt per count in the display. If,
for example, the THD is exactly 0.1% (-60dB), the
AA 501A will have autoranged to the 0.2% scale; a
reading of 0.1 000% and a FUNCTION OUTPUT of
1000 mV (1 \ rms will result.
TM 09361A-12
Applications— F7523A1 Mod WQ
7603
II
ii
II
II
SG505
AA501
o
O
OUT o
9
IN
gJj
SC50X
on
°
OoI
o qq
NP
OUT
9
O
op p
DO
coo
° O
O
0
°°
fool
O
OIN OIN
9 9O
O
0
O °o°° D
O
ao q °
qoq
pO 000 0
°
7L5
U
IN
oil
OUT
7813-47
Fig. 6.1.14. Spectrum analyzer driven from AA 501A Mod WO FUNCTION OUT connector.
The 0-dBV reference line on the spectrum analyzer will
thus be 60 dB below the signal fundamental and a 10 dB
per division vertical calibration will provide convenient
readings down to the 100 to -120 dB levels, where other
li mitations set in (to be discussed below). When the
AA 501 A Mod WQ autoranges or is manually ranged to a
higher scale, the same one-millivolt-per-count relationship holds at FUNCTION OUTPUT The 0-dBV reference
li ne on the spectrum analyzer that is -60dB (referred to
the AA 501A Mod WQ input signal) on the 0.2% range
becomes -40 dB on the 2%, -20 dB on the 20% range,
and 0 dB on the 100% range of the AA 501 A Mod WQ. It
is easy to determine which range the AA 501 A Mod WQ
has autoranged to by finding which button does not
change the decimal point's position in the display.
The one exception to a 0-dBV reference setting on the
spectrum analyzer occurs if any spectral-line peaks are
above the top (reference) graticule line of the spectrum
analyzer's CRT. This condition would occur only on percent THD readings between 01% and 0.2%, between
1 % and 2%, and between 10% and 20%. In these cases
the FUNCTION OUTPUT voltage will be between one
and two volts rms. Even then, depending on the individual harmonic amplitudes, displayed spectral lines
may not go above the reference line. If they do, go to a
+ 6-dBV (two-volt) reference and remember that the
reference-line-to-signal relationships are now -54dB,
-34 dB, or -14 dB respectively.
The ultimate limitations of the dual analyzer configuration cannot be rigidly specified, varying somewhat
from AA 501 A Mod WQ unit to unit, with temperature, and
with frequency. However, residual harmonic distortion at
the FUNCTION OUTPUT jack with fundamental frequencies between 20 Hz and 20 kHz is typically -100 to -115
dB at second and third harmonic and even less than
-115 dB at higher harmonics. Noise floors are a function
of spectrum-analyzer bandwidth, sweep rate, and
averaging; -120 dB is easily obtainable. Fig. 6.1.15 is an
example of a 7L5 spectrum-analyzer display when the
AA 501 A Mod WQ and 7L5 are measuring a . lowdistortion device. The 7L5 shows the suppressed fundamental at 1.6 divisions (16 kHz), second harmonic at
-98 dB, third at -104 dB, and a noise floor of approxi
mately -128 dB.
In harmonic-distortion analysis with the AA 501 A Mod
WQ and spectrum analyzer, it is normally convenient to
select a center frequency that places the suppressed
fundamental near the left of the screen and a span that
positions the first five to ten harmonics across the
screen. It is worth noting that the suppression of the
fundamental depends upon the amount of harmonic
energy present in the signal. The fundamental will
always be suppressed at least 10 dB below the
strongest harmonics and thus has a negligible effect on
the AA 501 A Mod WQ THD measurement. Likewise, it
will not limit the dynamic range of the spectrum analyzer.
The full fundamental rejection of 100 dB or more will
occur only when the signal harmonics are also 90 dB or
more below the fundamental.
6.1.17
TM 09361A-12
Applications—F7523A1 Mod WQ
7813-481
Fig. 6.1.15. Spectrum analyzer display with AA 501A Mod W0 and 7L5 distortion device.
Spectrum Analyzer Driven From AA 501 A
INPUT MONITOR Connector
This configuration (Fig. 6.1.16) does not increase the
effective dynamic range of the spectrum analyzer, since
no filtering precedes the INPUT MONITOR connector. It
does convert single-ended spectrum analyzers to differential input for good noise rejection. The constant
one-volt-mis signal level with any AA 501 A Mod WQ
input above 60 mV means the spectrum analyzer can be
set once for a 0-dBV (1 volt) reference and never
changed.
This configuration is generally used in intermodulation
testing when information on higher order products is
desired. For example, assume a Twin-Tone test is being
performed with frequencies 14 kHz and 15 kHz. The
AA 501 A Mod WQ in IMD mode will provide an automatic
digital readout of the amplitude of the second order
difference product at 1 kHz. If information is needed on
the second order sum at 29 kHz, third-order products at
13; 16, 43, and 44 kHz, or still higher-order products, a
spectrum analyzer must be used (see Fig. 6.1.17). The
constant output from the AA 501 A Mod WQ is particularly
convenient when IMD-versus-power-level tests are
being performed, since no adjustments of the spectrum
analyzer will be required after the initial 0-dBV setup.
6.1.18
Other intermodulation-testing techniques have been
proposed, though none is an accepted standard at this
writing. These techniques include three-tone tests,
combined sine-square tests, and phase-modulated
sawtooth tests. The AA 501 A Mod WQ INPUT
MONITOR—spectrum analyzer connection expedites
and simplifies any of these tests. However, as discussed
in the Cabot paper previously mentioned ("A
Comparison of Nonlinear-Distortion Measurement
Methods") SMPTE-like tests over an extended frequency range will quantify the same device short-comings
and are performed easily with the SG 505 Mod WQ and
AA 501 A Mod WQ without the complexity of a spectrum
analyzer.
Decibel-Converter Output
This signal provides a replica of the dc voltage after the
ac detector and dB converter that drives the digital display in all decibel-readout modes; the signal is present
even when a decibel display mode is not selected.
Source impedance is 1 kfl, and the scale factor is one
millivolt do per count displayed. Since display resolution
is 0.1 dB, this voltage equates to 10 mV dc per dB.
Polarity of this output voltage is exactly as in the display.
For example, a display of 40.3 dB would produce an output of 403 mV, and -63.7 dB yields -637 mV.
TM 09361A-.12
Applications— F7523A1 Mod WQ
audio-response sweeper package can be quickly
assembled from three standard TM 500 instruments as
shown in Fig. 6.1.18.
The decibel-converter output can be used to drive a storage oscilloscope in X-Y mode or a paper chart recorder
during swept-frequency-response testing. A complete
0o O
o
q O
qq
7603
q O
q
SG505
AA501
SC50X
O
O
O
of
0
DI IN
OUT a
O
o o
qqqq
0 qqq
INP FUNC
MON OUT
O
O
O
O
oq
qq
O
OINOIN 0
O
o
q
q
o °o O 7L5
q
000
o qq
O qqq
IN
•
I
i
OUT
7813-49
Fig. 6.1.16. Spectrum analyzer driven from INPUT MONITOR connector.
781
Fig. 6.1.17. Spectrum analyzer display showing second and third order products.
6.1.19
TM 09361A-12
Applications—F7523A1 Mod WO
AA501
LEVEL,
dB RATIO
FG507
20Hz - 20kHz
LOG SWEEP
O
qq
O
q q
oO
G
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G
iN
RAMP
OO
O
II 00
oq
O
Q q q q q p
q
^
q
0
OUT
X-Y
dB
OUT
Oq
O qq
O
SC503
o
o qoo
q q q q
X
(CH 1) O
000 o
Y
(CH 2)
9 9O
OUT
7813-51
Fig. 6.1.18. Audio-response sweeper package using AA 501A Mod WQ with FG 507 and SC 503.
The Sweeping Function Generator (FG 507 or FG 504)
provides a three-decade log sweep from 20 Hz to
20 kHz, and its linear-ramp output provides X-axis
deflection for the storage oscilloscope (or X-Y recorder,
if desired). The output of the device under test drives the
AA501 A Mod WQ input The AA 501 A Mod WQ, in Level
and dB RATIO modes, serves as detector and dB
converter. Its dB converter output drives the Y axis of the
storage scope.
Slow sweep speeds, on the order of 10 seconds or
longer, must be selected when sweeping from a 20-Hz
starting frequency if significant fm distortion is to be
Another possible application for the AA 501A Mod WQ
dB converter output would be in connecting the instru-
ment to a computer for data logging or manipulation. In
either THD + N, iMD, or LEVEL-dBm modes, this output
could be computer-interfaced via an appropriate
analog-to--digital converter. A convenient method would
be to use an inexpensive (perhaps talk-only) GPIB dc
voltmete with millivolt resolution on a one-or-two-volt
dc full scale. The fixed decimal location of the AA 501 A
Mod WQ in all dB modes simplifies system interfacing.
Decibel Conversion Limitations—Apparent
and Real
avoided. The AA 501A Mod WQ detector and dB
converter also have finite response times. If the device
Decibel displays in distortion, dBm, and dB RATIO
being tested has steep amplitude variations with
modes are provided by a log converter following the ac
detector. This converter has an effective dynamic range
frequency, sweep times up to one minute may be
necessary to provide accurate response
measurements.
For continuous sweep recordings, AUTORANGE should
not be used on the INPUT LEVEL RANGE switch, since a
glitch on the display will result each time the AA 501A
Mod WQ autoranges. Instead, the generator should be
manually swept to the frequency that produces maximum device-under-test output. This is extremely easy
with the MANUAL SWEEP mode of the FG 507, which
does not disturb sweep end points. The AA 501 A Mod
WQ INPUT LEVEL RANGE switch should then be turned
to the position at which neither the DECREASE RANGE
nor INCREASE RANGE LEDs are lighted, This will optimally position the 40-to-50-dB dynamic range of the dB
converter with respect to maximum signal. You can now
return the generator to triggered sweep and make a
response sweep.
6.1.20
of 40 to 50 dB, In certain applications, this dynamic
range sets performance limitations. In other cases, it
may appear to limit performance but actually does not.
This section explains the functioning of the AA 501 A Mod
WQ in these respects.
Autoranging of the AA 501 A Mod WQ involves manipulation of the decimal point's location and annunciator in
the digital display, adding precise dc offsets at the out
put of the dB converter, and gain/attenuator switching in
the instrument's front end. The AUTORANGING function
(or manual setting of the INPUT RANGE switch so that
both INCREASE/DECREASE RANGE indicators are off)
assures that the input to the detector is always between
2 V and 0.2 V mis except at AA 501A Mod WQ inputs
below 20 µV in LEVEL modes or distortion values below
0.01 % in THD and IMD modes. Thus, the dB converter is
normally working in the top 20 dB of its dynamic range.
As the input signal's amplitude is decreased, the
TM 09361A-12
Applications-F7523A1 Mod WQ
AA 501 A Mod WQ front end switches to keep detector
and dB-converter signal levels in their optimum range.
The switching also adds precise dc-offset voltages at
the dB-converter output so that the display shows the
absolute value of the signal.
Input-level sensing, which controls the autoranging,
occurs prior to all filtering. Selecting filters will thus not
change the attenuator range, but can change drastically
the signal level to the detector and dB converter. As an
example, assume an input-signal frequency of 50 Hz at
an amplitude of 0.775 V (0 dBm). Selecting the 'C' MSG
filter will attenuate the 50-Hz signal by typically 60 dB.
Selecting the 400-Hz high-pass filter will attenuate the
signal by typically 54 dB. When both are selected simultaneously, they are truly additive and the combined
attenuation will typically be 114 dB. However, the
AA 501A Mod WQ display will typically indicate only
about -50 to -60 dB due to the limited dynamic range
and low-level output noise of the dB converter. The
desired goal of attenuating 50-Hz components by
114 dB is occurring: their effect on a 1 kHz THD reading
or a noise reading is truly reduced by that amount. But,
due to the limited range of the dB converter, it cannot be
demonstrated by single frequency tests using the
AA 501A Mod WQ display. Thus, the limitation is only
apparent, not actual.
In applications where a fixed input range is selected,
however, the dB converter's dynamic-range limitation
becomes real. In the swept-frequency--,response application described above, for example, autoranging must
be defeated to avoid glitches on the display each time
the AA 501 A Mod WQ autoranges. On whichever manual
range is selected, the converter floor some 40 to 50 dB
below normal levels will mask measurements at still
lower levels, and the response time becomes progressively slower as the signal level approaches this floor.
Detector Output
The detector output provides a replica of the dc voltage
at the output of whichever detector, true RMS or AVG, has
been selected at the front panel. As with most other
inputs and outputs, the scale factor is one millivolt per
displayed count. Thus, for example, displays of 1.296 V,
129.6 µV, or 12.96% distortion would each produce
1296 mV (1.296 V) as the detector output. Source
i mpedance is 500 R.
Principal applications would be in swept frequency
response testing, as described above, if linear rather
than dB vertical display were desired. This output could
also be used via an A-to-D converter or GPIB voltmeter
to interface to a computer if linear data were needed.
However, instrument autoranging will cause the decimal
point to move in distortion measurements and both
decimal point and annunciators (VOLTS, mV, µV) to
change in LEVEL measurements. The dB converter output would be simpler to interface since no decimal point
or annunciator data would be needed by the computer,
even over the full dynamic range of the AA 501 A
Mod WQ.
As noted earlier, the AA 501A Mod WQ will not successfully track a continuously changing signal in THD+N
mode. If the detector output were to be used with a chart
recorder for plots of THD versus frequency, the pen
would have to be lifted before each frequency change
and lowered after the AA 501 A Mod WQ had settled at
each new spot frequency.
Twin -Tone
High-Frequency-Tone Output
This rear-interface output provides the high frequency
tone plus sidebands due to intermodulation by the low
frequency tone in Twirl-Tone IMD testing. The signal thus
follows the high-pass filter, which excludes the low
tones, but precedes the demodulator, which recovers
the sideband energy. Source impedance is 2 kfl; amplitude typically varies between 0.5 V and 3 V, depending
on input signal level and low-to-high amplitude ratio.
This output could be connected with a frequency counter
to measure only the high frequency tone, valuable in
extended IMD testing with higher frequencies than the
standard 7 kHz. This output, rather than the complex signal itself, can also be used to feed a spectrum analyzer,
adding 12 dB of dynamic range to the spectrum analyzer
for analysis of individual distortion products since the
low frequency tone.
Operator Traps
The AA 501A Mod WQ Distortion Analyzer and SG 505
Audio Oscillator were designed with humanengineering considerations playing an important part.
These instruments also provide excellent flexibility for
sophisticated measurements. Use within Tektronix has
shown that certain operator traps sometimes lead to a
nonfunctioning or apparently improperly functioning
instrument. Following is a list of several of these traps.
- Leaving the SG 505 Mod WR output switch in OFF
position following signal-to-noise measurements
- Selecting EXT Filter on the AA 501A Mod WQ, but
not connecting a filter
- Selecting any filter when inappropriate, especially
during frequency-response tests
6.1.21
Applications- F7523A1 Mod WO
- Selecting the Twin-Tone signal on the SG 505 Mod
WR when only a single sine-wave signal is desired
- Leaving the AA 501,E Mod WQ in IMD mode when
THD testing was intended
-- Sending a signal to the AA 501 A Mod WQ below
60 mV when THD testing is to be performed
Measuring low levels of external signals while either
SG 505 in the same mainframe is ON and set to high
amplitudes and/or high frequencies. Capacitive
coupling across the AA 501A Mod WQ REAR
6.1.22
TM 09361A®12
INTFC/INPUT switch will cause the SG 505 signal to
set a threshold preventing low-level measurements.
The cure is turning both SG 505 outputs OFF.
— Leaving either SG 505 GND/FLTG push button in the
GND position may increase distortion readings due
to noise pickup
Use of a dual-trace oscilloscope monitoring INPUT
MONITOR and FUNCTION OUTPUT, as described
earlier, has the additional benefit of quickly bringing to
the operators attention any of these traps except the
selection of EXT FILTER with no filter connected.
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