Tektronix 7L13 Instruction manual

Tektronix 7L13 Instruction manual
TEKTRONIX
7L13
SPECTRUM
ANALYZER
INSTRUCTION
Tektronix, Inc.
P.O . Box 500
Beaverton, Oregon
070-1673-00
97005
MANUAL
Serial Number
First Printing APR 1974
WARRANTY
All TEKTRONIX instruments are warranted against
defective materials and workmanship for one year.
Any questions with respect to the warranty, should
betaken up with yourTEKTRONIX Field Engineeror
representative .
All requests for repairs and replacement parts
should be directed to the TEKTRONIX Field Office
or representative in your area. This will assure you
the fastest possible service . Please include the
instrument Type Number or Part Number and Serial
Number with all requests for parts or service .
Specifications and price change privileges reserved .
Copyright c 1974 by Tektronix, Inc ., Beaverton,
Oregon . Printed in the United States of America . All
rights reserved . Contents of this publication may not
be reproduced in any form without permission of
Tektronix, Inc .
U .S.A . and foreign TEKTRONIX products covered
by U .S. and foreign patents and/or patents pending .
TEKTRONIX
is a registered trademark of Tektronix,
I
SECTION 1
TABLE OF CONTENTS
GENERAL INFORMATION & SPECIFICATIONS
Electrical Characteristics
Environmental Characteristics
Accessories
SECTION 2
1-2
1-4
OPERATING INSTRUCTIONS
Introduction
Function of the Front Panel Controls .
Operational Check
Using the Analyzer
Signal Application
Resolution, Sensitivity, and Frequency Span
Gain Desensitization Near 0 Hz
Using the Video Filter
Selecting Sweep Rate
Triggering the Display
Manual Scan of the Spectrum
How to Use an External Sweep Source
External Trigger Operation
Using the CAL OUT Signal Reference for Accurate
Frequency and Amplitude Measurements
Using the Analyzer Below 100 kHz
SECTION 3
Page
2-1
2-5
2-9
2-10
2-11
2-12
2-13
2-14
PERFORMANCE CHECK
Operational Performance and Instrument Familiarization
Equipment Required
Preliminary Preparation
Check the 10 dB/Div and LIN Mode Calibration
Check the Frequency Readout Accuracy
Check the Range of the REF VAR Control, the
Range and Accuracy of the Gain Selector, and
the Gain Accuracy of the 10 dB Pushbutton
Check the Operation of the Video Filters
Check Sensitivity
Check Spurious Signals from Internal Sources
(Residual Responses)
Check Resolution Bandwidth and Shape Factor
Check Incidental Wing
Check Sweep Circuit Operation with the TIME/DIV in the
MANUAL, and OFF Positions
Performance Checks Requiring Test Equipment
Equipment Required
Check the Calibrator Frequency
Check Calibrator Output Level
Check RF Attenuator Accuracy
Check Display Flatness
Check Intermodulation Distortion
Check Pulse Stretcher Operation
Check Triggering Operation and Sensitivity
Check The External Horizontal Input Voltage Requirement
Check the Video Output Level
Check Frequency Span Accuracy and Linearity
Check Time/Div Accuracy
3-1
3-2
3-3
3-5
3-6
3-7
3-9
3-10
3-11
3-12
3-13
3-14
3-15
3-16
TABLE OF CONTENTS (cont)
SECTION 4
CALIBRATION
Equipment Required
Short Form Procedure and Record
Time Base Section
Adjust Sweep Length, Offset, and Triggering
Function IF Alignment
Adjust the LIN Mode Baseline Offset
Adjust the Gain Compensation and Calibrate the
Reference Level
1st LO Phase Lock Loop
Error Amplifier Offset Adjustment
Frequency Span and 1st LO Calibration
Adjust the Frequency Span of the 1st LO and the
16-19 MHz Oscillators
Calibrate the Center Frequency and Frequency Readout
Phase Lock Calibration Adjustments
Adjust Memory Gain
Adjust Error Amplifier Gain
Resolution
Adjust the Bandpass of the 105 MHz IF Amplifier
and 300 kHz Filter
Adjust the Resolution Gain Leveling Compensation
Adjust the Post Resolution Amplifier Gain
Minimize Intermodulation Products
Page
4-1
4-3
4-6
4-8
4-10
4-11
4-12
4-14
4-16
50 MHz Calibrator
Adjust the Calibrator Output
SECTION 5
CIRCUIT DESCRIPTION
Block Diagram Description
Detailed Circuit Description
RF or Microwave Circuits
Phase Lock and Frequency Stablization
YIG Driver, Voltage Memory and Phase Lock Logic
Frequency Tuning Control and Readout
Tuning Control
YIG Driver
Frequency Span
Marker Generator
105 MHz IF Amplifier, 3rd Mixer and Oscillator
10 MHz IF Pre-resolution Amplifier and
Resolution Filter Circuits
YIG Oscillator Power Supply
30 Hz Filter
50 MHz Calibrator
Function IF Amplifier
Video Filter, Pulse stretcher, Baseline Clipper
& Vertical Output
Frequency Readout
Uncal Circuit
Sweep Triggering Sweep Generator and
Horizontal Amplifiers
5-1
5-2
5-3
5-4
5-5
5-6
5-7
5-8
5-9
5-11
5-12
TABLE OF CONTENTS (cont)
SECTION 6
MAINTENANCE INSTRUCTIONS
Page
Preventive Maintenance
Cleaning
Lubrication
Visual Inspection
Transistor and Integrated Circuit Checks
Performance Checks and Recalibration
6-1
Troubleshooting
Troubleshooting Aids
Diagrams
Circuit Board Illustrations
Wiring Color Code
Multiple Terminal (Harmonic) Connector Holders
Resistor Code
Capacitor Marking
Diode Color Code
Transistor and Integrated Circuit Electrode Configuration
Diode Checks
IC Checks
General Troubleshooting Techinque
Corrective Maintenance
Obtaining Replacement Parts
Repair and Exchange Program
Soldering Technique
Replacing Square Pins for Multi-pin Connectors
Replacing Assemblies
Front Panel Controls and Selectors
Circuit Board Assemblies
DVM Logic and Readout Circuit Board
Replacing the Sweep Circuit Board
Replacing the IF Function Circuit Board
Replacing the Resolution Circuit Board
Replacing Circuit Boards in the Honeycomb Assembly
Replacing Microwave Assemblies
Replacing the 2.095 GHz Filter Assembly A10,
or the Multiplier-Bandpass Filter A401
Replacing the Multipler 2.18 GHz Bandpass
Filter and 16-19 MHz Mixer Circuit Board Assembly
6-2
SECTION 7
OPTIONS AND MODIFICATIONS
SECTION 8
ELECTRICAL PARTS LIST
SECTION 9
DIAGRAMS AND CIRCUIT BOARD ILLUSTRATIONS
SECTION 10
MECHANICAL PARTS LIST
CHANGE INFORMATION
6-3
6-5
6-6
6-8
6-10
6-11
6-13
Fig. 1-1 . 71-13 Spectrum Analyzer.
Section 1-71-13
GENERAL INFORMATION
AND
SPECIFICATIONS
INTRODUCTION
Abbreviations used in the text and diagrams are based
on ANSI Y 1 .1, 1972 Standards . This manual is divided into
ten major sections that provide the following information :
Section 1 - General Information and Specifications :
Contains the instrument description and specifications .
Section 2 - Operation Instructions : Information
relative to installing and operating the instrument.
Section 3 - Performance Check: Provides procedures
to check the operational performance of the instrument
plus additional performance check procedures that require test equipment to verify that instrument performance is in accordance to specifications .
Section 4 - Calibration Procedure : Describes test
equipment setup and adjustment procedures required to
calibrate the instrument .
Section 5 - Circuit Description : Provides basic and
general circuit analysis that may be useful when servicing
or operating the instrument .
Section 6 - Maintenance Instructions : Describes
routine and corrective maintenance procedures with
detailed instructions for replacing assemblies, subassemblies, and individual components. Troubleshooting
procedures, plus general information that may aid in
servicing the instrument, are also provided . An exploded
drawing is part of Section 10 .
Section 7 - Options : Describes options available for
the instrument.
Section 8 - Electrical Parts List : Provides information
necessary to order replaceable parts and assemblies.
Section 9 - Diagrams: Provides functional block
diagram and detailed circuit schematics. Located adjacent to the diagram (usually on the back of the preceding
diagram) are pictoral layout drawings that show sub-
assembly and component locations . IC logic diagrams,
waveforms and voltage data, for troubleshooting orcircuit
analysis, are also provided adjacent to or on the diagram .
Section 10 - Mechanical Parts List, Exploded
Drawings and Accessories : Provides information
necessary to order replaceable parts. The Parts List is
cross-referenced to the Electrical Parts List . Exploded
drawing shows sequence of assembly and identifies
assemblies.
Changes and Corrections : Provides updating information for the manual in the form of inserts. These inserts are
incorporated into the manual text and diagrams when the
manual is reprinted .
DESCRIPTION
The 71-13 Spectrum Analyzer is a high-performance
communication spectrum analyzer that plugs into and
operates with the 7000-Series mainframe oscilloscopes . It
is a swept front end analyzer that displays absolute
amplitude information of signals within the frequency
span of 0 Hz to 1 .8 GHz. Time domain characteristics,
within a 3 MHz bandpass, can also be displayed .
Important features of the 71-13 are : 1) Greater than
70 dB dynamic range. 2) Sensitivity down to -128 dBm .
3) Resolution capability from 3 MHz to 30 Hz.
4) Incidental Wing less than 10 Hz . 5) Fully calibrated
display modes of either 10 dB/Div, 2 dB/Div, or Linear ;
and a calibrated reference level in dBm . 6) Calibrated
sweep spans from 100 MHz/Div to 200 Hz/Div . 7) Digital
frequency readout . 8) Full range of video filtering for noise
averaging . 9) Baseline clipping to subdue the bright
baseline of displays when photographing . 10) Pulse
stretching, to enhance pulsed spectra when using wide
frequency spans and resolution bandwidths . 11) Access
for a tracking generator . 12) Frequency and amplitude
reference calibrator.
If the 7000-Series mainframe features crt readout, the
signal parameters and other pertinent information, such
as resolution bandwidth, video filtering, and frequency
span, are displayed on the crt readout to simplify the
operation of the instrument. Records can then be made of
pertinent data by photographing the display .
Specification-7L13
The analyzer requires three plug-in widths in the 7000Series mainframe.
ELECTRICAL CHARACTERISTICS
The following characteristics and features of the 7L13
Spectrum Analyzer are applicable after a warmup period
of 30 minutes or more .
CENTER FREQUENCY
Range: 1 kHz to 1 .8 GHz.
Resolution of the Center Frequency Indicator: Within
1 MHz.
STABILITY (after a 2 hour warmup period)
Within 2 kHz per hour at a fixed temperature, when
phase locked ; within 50 kHz when not phase locked .
INCIDENTAL FM (see Fig. 3-5)
10 Hz (peak-to-peak) or less when phase locked, and
10 kHz (peak-to-peak) or less for 5 seconds when out of
phase locked mode .
VIDEO FILTERING
Three selections of video filtering; 10 Hz, 300 Hz and
30 kHz are provided for signal or noise averaging .
DISPLAY
Accuracy : f(5 MHz + 20% of the Freq Span/Div) .
The center frequency is indicated by LED readout on
the 7L13 and crt readout when the 7000-Series mainframe
has this feature.
FREQUENCY SPAN
Calibrated spans from 200 Hz/Div to 100 MHz/Div in a
1-2-5 sequence, plus O Hz and MAX SPAN positions. In the
0 Hz position, the analyzer is a fixed tuned receiver for
time domain analysis . In the MAX SPAN position the
frequency span is approximately 1 .8 GHz.
Accuracy : Within 5%of the indicated frequency separation . Linearity over the center 8 divisions is within 5% .
RESOLUTION
Six resolution bandwidth selections from 30 Hz to
3 MHz, in decade steps, are provided . Resolution
bandwidth may be coupled or uncoupled from the frequency span selector .
Bandwidth accuracy : Resolution bandwidth, at the
6 dB down point, is within 20% of the resolution selected .
Shape factor (60:6 dB ratio) : 12 :1 or better for 30 Hz
resolution and 4:1 or better with resolution of 300 Hz or
more except 3 MHz. Maximum bandwidth 60 dB down
with 3 MHz resolution, is 13 MHz.
LOG 10 dB/DIV : Provides a calibrated 70 dB dynamic
range with an accuracy that is within 0.1 dB/1 dB to a
maximum of 1 .5 dB over the full dynamic range.
LOG 2 dB/DIV : Provides a calibrated 14 dB dynamic
range with an accuracy that is within t0 .4 dB/2 dB to a
maximum of 1 .0 dB over the 14 dB dynamic range.
LIN: Provides a linear display from approximately
0 .7 /jV (100 dBm) full scale, to 7 .07 volts (+30 dBm) .
Amplitude linearity is within 10% over the graticule height .
REFERENCE LEVEL
Reference level operation is in calibrated 10 dB steps
from -110 dBm to +30 dBm, within t2 dB . (Accuracy
includes the attenuator and gain switching effects when
the two are not offsetting each other.) Reference level
operation below 100 kHz becomes limited to a rangefrom
+30 dBm to-50 dBm as the center frequency approaches
1 kHz.
Reference level deviation, between display modes, is
less than 2 dB from 2 dB/DIV to 10 dB/DIV and less than
0.5 divisions from 2 dB/DIV to LIN. This deviation is a
function of the oscilloscope vertical linearity.
An LINCAL indicator signifies when the display is not
calibrated .
DISPLAY FLATNESS
Signal level change over the six resolution bandwidth
selections is less than 0.5 dB .
+1 dB, -2 dB with respect to the level at 50 MHz, over
any selected frequency span .
'^
Specification-7L13
CALIBRATOR
50 MHz ±0 .01% with an absolute amplitude level of
-30 dBm ±0 .3 dB, at 25°C . 50 MHz harmonics are
generated to provide a comb of markers for frequency
span calibration .
CW SENSITIVITY (Signal + noise = 2x noise, In LIN
display mode)
The following characteristics are applicable from
100 kHz to 1 .8 GHz: Below 100 kHz the sensitivity
degrades approximately 0.3 dB/kHz ; for example, the
sensitivity at 50 kHz with 30 Hz resolution is, -113 dBm or
better; at 1 kHz, -98 dBm or better .
RESOLUTION BANDWIDTH
30
300
3
30
.3
3
Hz
Hz
kHz
kHz
MHz
MHz
SIGNAL LEVEL
-128
-120
-110
-100
-90
-80
dBm
dBm
dBm
dBm
dBm
dBm
positions provide an additional 40 dB of gain only in the
2 dB/DIV and LIN modes. The 10 dB pushbutton provides
the additional 10 dB of gain, when the resolution bandwith
is 30 Hz and the REFERENCE LEVEL is -100 dBm in the
2 dB/DIV or LIN mode .
The REF VARiable control provides continuous gain
adjustment between each calibrated REFERENCE LEVEL
setting.
RFATTENUATOR
Provides 60 dB of attenuation in calibrated 10 dB steps.
Accuracy is ±0 .2 dB or 1 % of the dB reading, whichever is
greater .
MAXIMUM INPUT POWER LEVEL
-30 dBm with the RF Attenuator at 0 dB, for linear
operation, +30 dBm with the RF Attenuator at 60 dB .
(+30 dBm is also the power rating of the RF Attenuator .)
NOTE
SPURIOUS SIGNALS FROM INTERNAL SOURCES
(Residual Response)
Equal to or less than -100 dBm, referred to the 1st
mixer input.
INTERMODULATION DISTORTION (Fig . 3-6)
100 kHz - 1 .8 GHz: Third order intermodulation
products are down 70 dB or more from two -30 dBm
signals within any frequency span, second order products
are down 70 dB or more from two -40 dBm signals within
any frequency span .
100 kHz - 1 kHz: Intermodulation products (3rd and
2nd) are down 50 dB or more for the same input level as
above.
GAIN
The gain range is 80 dB total . An eight position selector
changes the IF gain 70 dB in 10 dB (±1 .0 dB) steps and a
10 dB pushbutton adds an additional 10 dB of gain when
the REFERENCE LEVEL is -100 dBm and 30 Hz resolution bandwidth is used, in the 2 dB/DIV or LIN mode .
Four positions (blue sector) of the selector provide
30 dB of change in all display modes. The remaining four
The maximum input power level to the RFA ttenuator
is 1 watt average and 200 watts peak. +13 dBm will
destroy the 1st mixer.
SWEEP MODES AND RATE
Selection of an external sweep source, manual sweep,
or calibrated sweep rates from 10 s/Div to 1 ps/Div in a 12-5 sequence are provided . Sweep rate accuracy is within
5% of that selected .
TRIGGERING
Three triggering sources can be selected . INTernal
selects the vertical or video component from either vertical
plug-in compartment, EXTernal selects the signal applied
to the EXT IN HORIZ/TRIG connector and LINE selects a
sample of the mainframe line voltage . INTernal signal is ac
coupled with an approximate frequency range from 15 Hz
to 1 MHz. The external and line signals are do coupled .
Input impedance for the external input is about 30 kid for
the trigger mode and 9 kQ for external horizontal sweep
mode .
Trigger sensitivities are: 1) <0 .5 division of internal
signal (peak-to-peak) and <0 .5 volt of signal (peak-topeak) of external signal for NORM mode . 2) <0 .5 division
of internal signal peak-to-peak and <0 .5 volt of external
signal for SGL SWP mode .
Specification-71-13
In the NORM mode the sweep will automatically recur
at the end of holdoff time if a trigger signal is absent, to
provide a baseline on the crt.
The SGL SWP and "start" buttons function together to
provide a single sweep each time the "start" button is
pushed .
VIDEO OUTPUT CONNECTOR
Provides 50 mV t5% of video signal per display
division, aboutthe crt vertical center. Source impedance is
approximately 1 kit. A maximum of 50 mV offset may be
introduced by the error from the mainframe vertical
centering interface .
ACCESSORIES AND OPTIONS
STANDARD ACCESSORIES
1 . Spectrum Analyzer Graticule: Clear plastic implosion shield with LOG, LIN, REF and f (frequency) direction
markings. Tektronix Part No. 337-1439-01 for 7403N
oscilloscope and 337-1159-02 for other 7000-Series oscilloscopes.
2. Filter Light Amber
378-0684-01
3. 50 i2 Coaxial Cable,
with BNC connectors, 6 foot
012-0113-00
4. BNC Male to N Female Adapter
103-0058-00
5. Manual
070-1673-00
HORIZONTAL/TRIGGER
INPUT
EXTERNAL
CONNECTOR
Requires 0 V to 10 V t1 V, to sweep the full frequency
span .
OPTIONAL ACCESSORIES
1 . DC Block (for applying
signals riding on a DC potential) . Maximum potential is
50VDC
Requires 0.5 volt peak-to-peak to trigger the sweep
circuits . Maximum safe input; 50 volts (dc + peak ac) .
2 . 75 0 to 50 i2 minimum loss
attenuator with DC block
ENVIRONMENTAL CHARACTERISTICS
This instrument will meet the electrical characteristics
over the environmental limits of the 7000-Series mainframe. Complete details on test procedures, including
failure criteria, etc., can be obtained from Tektronix, Inc.
Contract your local Tektronix Field Office or representative .
015-0221-00
011-0112-00
OPTIONS TO 7000-SERIES OSCILLOSCOPES
1 . CRT with P7 phosphor and time domain graticule .
The external graticule for spectrum analysis (part of
standard accessories) should be used.
2. CRT with P7 phosphor and an internal spectrum
analyzer graticule (designated P7SA). This is
recommended when the oscilloscope mainframe is to be
used exclusively with spectrum analyzer systems .
Section 2-71-13
OPERATING INSTRUCTIONS
INTRODUCTION
This section describes : 1) Function of the front panel
controls, selectors,
indicators and
connectors .
2) Installation of the 71-13 into a 7000-Series oscilloscope .
3) General operation information, such as : Adjustments
required to mate the 71-13 to a 7000-Series oscilloscope .
Signal application to the RF INput. How to use the
calibrator for accurate frequency and power level
measurements, etc . 4) Some typical applications .'
The first steps of the General Operating information
calibrate and check the analyzer Frequency, Span/Div,
and the display modes . These steps serve as part of an
acceptance check and describe how to obtain a display on
the oscilloscope crt .
Performing this Operational Checkout procedure will
acquaint you with the functions of the controls and
selectors and the overall operation of the 71-13.
A safety latch must be released before the 71-13 can
be pulled from the oscilloscope compartment. The
unit will pull out part way, when the front panel
release is pulled, then the spring safety latch mustbe
pushed up to free the unit so it can be pulled the rest
of the way out. This safety latch is located underneath the right rail near the front corner (see
Fig . 2-113) .
FUNCTION OF THE FRONT PANEL
CONTROLS AND ADJUSTMENTS
The following is a general description of the 71-13
controls, indicators and connectors. This description will
familiarize you with theirfunction and Figs . 2-1Aand 2-1 B
illustrate their location .
A MARKER indicator lights when the FREQ SPAN/DIV
is at the MAX SPAN position and a notch on the baseline of
the display indicates the center portion of the span that
will be displayed when the FREQ SPAN/DIV is reduced.
The center frequency or marker frequency is indicated
by an LED digital readout dial .
CAL : Calibrates the frequency readout so it represents
the center of the span .
NOTE
When operating with Freq Spans of 50 kHz/Div or
less, the AUTO PHASE LOCKED switch must be
OFF if you want the center frequency and LED
readout to change when tuning .
FREQ SPAN/DIV : This switch selects the frequency
span of the display. The calibrated range of the selector is
100 MHz/DIV to 200 Hz/DIV in a 1, 2, 5 sequence . A MAX
SPAN position provides approximately 1 .8 GHz of spectrum and a 0 Hz position converts the analyzer to a fixed
tuned receiver for time domain displays . Time analysis of
the signal characteristics, within the bandwidth
capabilities selected with the RESOLUTION control, can
then be performed.
The FREQ SPAN/DIV knob is large enough to
provide ease in switching; however, excess torque
applied when the selector is at either of its extreme
positions may cause the aluminum bushing inside
the knob to slip. When this occurs, the selectors may
double detent or switch with a grinding noise. Refer
to Knob Removal and Installation instructions in the
Maintenance section of the manual for realignment.
FREQUENCY CONTROLS
TUNING : The center frequency is tuned by a two-speed
control with a ratio of approximately 1 :2.8 in the position
and 45 :1 in the slow orfine position . In addition, the tuning
range is decreased to 1 MHz (±9500 kHz) when the FREQ
SPAN/DIV is 50 kHz or less.
I A treatise on spectrum analyzer measurements and applications
Is contained In Tektronix Measurements Concepts Booklet;
"Spectrum Analyzer Measurement Theory and Practice :", Part
No. 082-1334-00 .
RESOLUTION : This control selects the resolution
bandwidth for the analyzer . The calibrated range (within
20%) is 30 Hz to 3 MHz in decade steps . The
RESOLUTION is normally coupled to the FREQ
SPAN/DIV control so the display amplitude remains
constant as the FREQ SPAN is changed ; however, a
concentric sleeve labeled PULL TO UNLOCK will uncouple the two selectors when it is pulled out and allow
independent settings of each control .
Operating Instructions-7L13
Fig . 2- 1 A . Front panel controls and selectors.
Operating Instructions-7L13
Fig. 2-28 . Front panel controls and selectors.
2-3
Operating Instructions-71
.13
DISPLAY CONTROLS AND SELECTORS
LOG 10 dB/DIV : Selects a calibrated display with a
dynamic range of 70 dB (to the 7th graticule line, from the
reference) at 10 dB/DIV . The bottom graticule division is
not calibrated .
reference level. The dynamic range of the display is now
-114 dBm (-100 dBm + 14 dB display window to the 7th
graticule line) . An additional 10 dB of gain, fora calibrated
-124 dBm, can be switched in with the 10 dB GAIN
pushbutton, when the RESOLUTION is 30 Hz .
LOG 2 dB/DIV : When this pushbutton is depressed, the
dynamic range of the display is a calibrated 14 dB at
2 dB/DIV .
VIDEO FILTERS : Three filters (30 kHz, 300 Hz, and
10 Hz) can be switched in to restrict the video bandwidth
and reduce high frequency components for display noise
averaging . Two pushbuttons select 30 kHz or 300 Hz
when depressed, and 10 Hz when both are depressed.
LIN : Selects a linear display. The LIN graticule calibration permits relative signal level measurements as follows:
Adjust the level of one signal to the 1 .0 line, with the gain or
RF Attenuation . Read the level of the other signals as a
percentage of this reference.
BASELINE CLIPPER: This controls the vertical
amplitude of that portion (baseline plus signal) of the
display that the intensity is subdued.
REFERENCE LEVEL (RF Attenuator and IF Gain) :
These are concentric controls that are connected in an
electro-mechanical differential arrangement. They select
input attenuation to the input mixer, and the IF gain . They
indicate, via readout windows; REFERENCE LEVEL in
dBm, of the full scale display, MAXimum signal input level
(in dBm) for linear operation, and the input RF attenuation
(from 0 to 60 dB) .
The RF attenuation is in series with the input signal path
to the input mixer, therefore its settings affect the
maximum input signal level to the 71-13 . With 0 dB
attenuation, maximim input signal level for linear operation, is -30 dBm . Changing the RF Attenuator to 60 dB
increases the maximum input signal level to +30 dBm .
The IF gain selector has a range of 70 dB in 10 dB steps.
The combination of RF Attenuator and IF gain settings
establishes the REFERENCE LEVEL ; therefore, both
controls function as REFERENCE LEVEL selectors. The
maximum sensitivity of the display will not exceed
-130 dBm . Since the dynamic window is 70 dB in the
10 dB/DIV display mode, the REFERENCE LEVEL
readout is valid to -60 dBm. With the RF Attenuator at
0 dB and the IF gain fully ccw, the REFERENCE LEVEL is
-30 dBm . Increasing the IF gain 30 dB, changes the
REFERENCE LEVEL to -60 dBm, which is the limit for a
calibrated reference level in the 10 dB/DIV mode . The blue
tint, that borders the 10 dB/DIV switch and four positions
of the gain selector, correlates REFERENCE LEVEL
readout to the gain settings applicable in the 10 dB/DIV
mode. Readings, with the gain selector outside the blue
tint sector are erroneous because the gain is electrically
locked out; the crt readout will display the < symbol to
signify that the reading is incorrect.
In the 2 dB/DIV mode, the full 70 dB range of the gain
selector is usable . Switching the gain fully cw with the RF
Attenuator at 0 dB, produces an accurate -100 dBm
2-4
CONTRAST : Adjusts the brightness ratio between the
clipped (subdued) baseline and the unclipped display.
The display intensity is set by the mainframe Intensity
control .
PULSE STRETCHER: Switching this on, stretches the
falltime of pulsed signals to enhance the visibility of
pulsed RF signals that may be within wide frequency
spans and resolution bandwidths .
LOG and AMP CAL: The LOG adjustment calibrates the
logarithmic accuracy of the display. The AMP adjusts the
REFERENCE LEVEL to the top graticule line .
AUTO PHASE LOCKED : This switch is used to disable
the phase lock for some applications, such as tuning the
analyzer more than 1 MHz when the analyzer is used as a
tuned receiver (0 span) .
VERTICAL POSITION : Positions the crt beam vertically.
HORIZ POSITION : Positions the crt beam horizontally .
OUTPUT AND INPUT CONNECTORS
VIDEO OUT: Provides ±50 mV of video per displayed
division of signal . The amplitude and polarity of this signal
is relative to the graticule vertical centerline . Source
impedance is about 1 kf2. This signal can be used to drive
an external device such as a recorder .
TRACK GEN: A source of control signals for a Tracking
Generator. Pin 5 of the connector is the source of a +10 V
to -10 V sweep ramp, with +10 V representing the left
edge of the display and -10 V the right side of the display.
Operating Instructions-71
.13
RF IN : A 50 f2 input connector for applying the input
signal to the 71-13. REFERENCE LEVEL readout refers to
the signal level at this connector . Any signals riding on
some do potential must be applied through a do block.
Refer to the General Operating Procedure with regard to
signal applications .
1st and 2nd LO OUT: These connectors provide access
to the output of the respective local oscillators . They must
be terminated into 50 O. Keep the termination plugs on the
output jacks unless these ports are connected to an
external device such as a tracking generator.
CAL OUT: Provides an accurate -30 dBm, 50 MHz
signal source . This signal provides an absolute reference
on the display to calibrate the REFERENCE LEVEL and
check dBm readings . Harmonics of the 50 MHz fundamental provide a comb of markers across the frequency
span for accurate frequency and span measurements .
SWEEP CONTROLS
TRIGGERING SOURCE : Three sweep triggering
sources can be selected plus a free run mode : INTernal
selects the vertical orvideo component from eithervertical
plug-in compartment. The signal is ac coupled with an
approximate frequency range from 15 Hz to 1 MHz;
EXTernal selects the signal that is applied to the EXT IN
HORIZ/TRIG connector; and LINE selects a sample of the
mainframe line voltage . External and line signals are do
coupled to the triggering circuits . Maximum signal input
to the external input connector should not exceed 50 volt
(dc + ac peak) for triggering . Input impedance for the
external input is about 30 kf2.
The FREE RUN mode will not sync the sweep to any
triggering signal .
MODE : Two modes are available, NORM and SGL
SWP. In the NORM mode the sweep will automatically
recur at the end of holdoff time, if a trigger signal is absent .
This feature provides a baseline on the display. In this
mode triggering occurs at the slope and level selected by
the SLOPE/LEVEL controls unless the triggering signal is
below the required amplitude or beyond the frequency
limits of the circuit. Minimum signal amplitudefor internal
triggering is 0.5 division of signal (peak-to-peak) and
0.5 volt of signal for external triggering .
In the SGL SWP mode, the sweep is triggered by
pushing the adjoining button . This button lights during
sweep time and serves as an indicator to determine
camera shutter time when photographing slow scan-time
displays . Minimum signal amplitude for triggering is
0.5 division of signal and 0.5 volt of external signal .
TIME/DIV and MANUAL SCAN : Three sweep modes,
plus an off state, are provided : A calibrated TIME/DIV in a
1, 2, 5 sequence from 10 s/DIV to 1 Ns/DIV, a manual
sweep control, and an external sweep . The TIME/DIV
control selects the sweep rates and the modes.
In the OFF position, the crt beam is horizontally
centered and the analyzer becomes a fixed tuned receiver
at the frequency indicated by the readout.
The EXT position connects any signal applied to the
EXT/HORIZ TRIG connector to the horizontal deflection
circuits of the 71-13. External sweep voltage (0 V to 10 V)
signal can be used to slave the 71.13 to an external device
such as a recorder .
The MANUAL position connects the sweep circuits of
the 71-13 to the MANUAL SCAN control, so the crt beam
deflection can be manually controlled .
SWEEP CAL : The adjustment calibrates the amplitude
of the sweep voltage to the FREQ SPAN circuits and
compensates for differences in deflection sensitivities
between oscilloscopes.
OPERATIONAL CHECK
that
1 . Preliminary
Operational
Procedure
Mainframe
Calibrates the 71-13 to the Osciliscope
When the 71_13 plug-in unit is installed in a 7000-Series
mainframe, the spectrum analyzer should be calibrated to
ensure correlation between plug-in and the mainframe
deflection sensitivities. We recommend that the front
panel calibration procedure be performed anytime the
instrument is first turned on, to ensure optimum accuracy .
a. Plug the 71-13 Spectrum Analyzer into the 7000Series mainframe. Ensure that the 71-13 is securely latched
in the compartment. This is a safeguard to ensure that the
instrument does not slide out, if the mainframe is tipped
forward.
NOTE
A safety latch is used to reduce the possibility of the
instrument slipping out of the mainframe.
b. Connect the oscilloscope mainframe to a suitable
power source and switch the power on . Allow about 30
minutes for instrument stablization .
2- 5
Operating Instructions-71
.13
c. Set the front panel controls as illustrated in Fig . 2-2
and connect the CAL OUT signal through a short coaxial
cable to the RF INput .
3. Calibrate the Sweep Span
d . Adjust the oscilloscope Intensity, Focus and
Astigmatism controls for optimum display definition with
normal intensity.
b. Position the 0 Hz response, or LO feedthrough, on
the zero (left) graticule line with the HORIZ POSITION
control .
e. Depress the 2 dB/DIV display mode button . Position the baseline of the display to the bottom graticule line
with the VERTICAL POSITION control and center the
display with the HORIZ POSITION control.
c. With the CAL OUT signal applied to the RF INput,
decrease the FREQ SPAN/DIV to 50 MHz and tune the 5th
marker (250 MHz) to the center graticule line (see Fig . 23) .
f. Depress the 10 dB/DIV (LOG) display button .
Display should now resemble that shown in Fig . 2-2.
d . Calibrate the frequency span to 50 MHz/DIV by
adjusting the SWP CAL for 1 marker/division. It may be
necessary to keep the 250 MHz marker centered with the
frequency TUNING control as the sweep is calibrated .
Final display should resemble that illustrated in Fig. 2-3.
NOTE
When the oscilloscope has a crt with P7 phosphor, a
viewing hood will help shield ambient light and
enhance the display information.
2. Calibrate the Frequency Readout
Due to hysteresis in the tuning system, the calibration
and accuracy of the readout must be performed and
checked by approaching each check point from the same
direction (low to high) .
a. Apply the calibrator signal to the RF INput, switch
the FREQ SPAN/DIV to MAX SPAN, and tune the CENTER
FREQUENCY to 0000.
b. Decrease the FREQ SPAN/DIV setting to 10 MHz
and increase the CENTER FREQUENCY until the 50 MHz
calibrator signal is tuned to thecenterl ine of the graticule.
NOTE
a. Switch the FREQ SPAN/DIV to MAX SPAN position .
4. Check and Adjust LOG-AMPL Calibration
The LOG CAL adjustment calibrates the gain of the
analyzer vertical output so the 2 dB/DIV and 10 dB/DIV
modes may be accurately set . The AMPL CAL adjustment
sets the reference level to thetop graticule line . There is no
interaction between these two, adjustments .
a. Set the 71-13 selectors and controls as directed in
step 2 and tune the fundamental 50 MHz calibrator signal
to the center of the graticule .
b. Uncouple the RESOLUTION selector from the
FREQ SPAN/DIV by pulling out the PULL TO UNLOCK
sleeve, then switch the FREQ SPAN/DIV to 5 MHz. The
RESOLUTION should remain at 3 MHz. As the FREQ
SPAN is decreased, it may be necessary to re-adjust the
tuning control to keep the signal centered on screen .
c. Switch the Display Mode to 2 dB/DIV and position
the baseline of the display on the bottom gratiucle line
with the VERTICAL POSITION .
It is important to tune the signal from low to high . If
the tuning direction is reversed, repeat the
procedure by returning the FREQ SPAN/DIV to MAX
SPAN and the CENTER FREQUENCY to 0000 to
establish the same reference point on the hysteresis
loop .
d. Adjust the AMPL CAL and the LOG CAL (if
necessary) to bring the 50 MHz signal within the graticule
window . Adjust the AMPL CAL to establish a signal
reference amplitude of 8 divisions (Fig . 2-4 shows a full
screen display) .
c . When the 50 MHz signal is centered on screen,
adjust the frequency CAL for a CENTER FREQUENCY
readout of 50 MHz.
e. Switch in 10 dB of attenuation with the RF
Attenuator . Amplitude change should equal 5 divisions at
2 dB/DIV .
2- 6
'~
-
Operating Instructions-71-13
CENTER
FREQUENCY
RESOLUTION
Top line is dBm level
indicated by REFERENCE
LEVEL window and
Readout .
Display Mode : 10 dB/DIV
Frequency : 250 MHz
UNCAL Light OUT
RF Attenuator : 0 dB
Sleeve pushed in so
FREQ SPAN/DIV and
RESOLUTION are
coupled together .
FREQ SPAN/DIV : 50 MHz
PULSE STRETCHER Out
Termination caps on
Output Ports
CAL OUT : Connect to
RF Input
Fig . 2-2 . Front panel selector positions and signal connections for initial operational check and front panel calibration .
Operating Instructions-71-13
Set the 250 MHz (5th) marker at
the centerline with the HORIZ
POSITION control .
0 Hz response
I-Jodam
0I"M IM, J 1 MHz, pz
g . Switch out the 10 dB of RF Attenuation . Now adjust
the AMPL CAL to return the signal level to the reference
line . (Ensure that the baseline of the display is still on the
bottom graticule line .)
h . Repeat these steps until the 2 dB/DIV display is
calibrated (see Fig . 2-4), then return the RF Attenuator to
0 dB (REFERENCE LEVEL -30 dBm) . Ensure that the
-30 dBm signal is 8 divisions in amplitude .
11
11
1I1
"
,s'~
1
,ll,
NOTE
ll~"
An alternate method of calibrating the display is to
switch between the 10 d8/DIVand2 d8/DIVdisplay
modes while adjusting the LOG CAL so the display
amplitudes are equal, then adjust the AMPL CAL so
the display amplitude, in 2 d8/DIV mode, equals
-30 dBm reference. Check the final calibration in
the 2 d8/DIV mode .
Fig . 2-3. Calibrating the sweep span .
2) Adjust AMP CAL to
position -30 dBm signal
to the REFERENCE
LEVEL (top graticule
line) .
-J(~dDm
40
050
_J
__ __ T
,
~MHZI Ai:S
k,
1) Adjust LOG CAL for
10 dB amplitude change
with 10 dB change in
RF Attenuator .
5. Check the 10 dB/DIV and LIN Mode Display
Operation
-so
Baseline of the display must be
positioned on the bottom
graticule line .
Fig . 2-4 . Calibrating the LOG and REFERENCE LEVEL . (Double
exposure to illustrate the relationship of the two displays .)
f. If the change is more than 5 divisions (e .g .,
amplitude decreases from 8 to 2 .5 div), adjust LOG CAL to
further increase the amplitude change (i .e ., decrease the
signal amplitude) . Conversely, if the change is less than
5 divisions (e .g ., amplitude changes from 8 to. 3.5 div),
adjust the LOG CAL to further decrease the amplitude
change (i .e ., increase the signal amplitude) . Correct for
approximately 1/2 the total indicated error. This adjustment may seem opposite to what is expected ; however, the
LOG CAL adjustment also shifts the reference level . This,
therefore will require a correction to the amplitude
change .
2- 8
i. Switch the display modes from 2 dB/DIV to
10 dB/DIV, then from 2 dB/DIV to LIN. Signal amplitude
reference level should not change more than 2 dB from
2 dB/DIV to 10 dB/DIV, or 0 .5 division from 2 dB/DIV to
LIN mode .
a . After completing the LOG CAL and AMPL CAL
adjustments, described in step 4, depress the 10 dB/DIV
button . Ensure that the RF Attenuator is at 0 dB and the
Gain selector is fully ccw so the REFERENCE LEVEL
reads -30 dBm .
b. Switch the FREQ SPAN/DIV to 1 MHz and the
RESOLUTION to .3 MHz. Tune the 50 MHz marker to the
graticule center .
c . Increase the RF Attenuator setting in 10 dB steps
and note that the signal amplitude decreases 1 divison
each step .
d . Switch the RF Attenuator back to 10 dB, and
depress the LIN display mode button .
e . Ensure that the baseline of the display is at the
bottom graticule line, and the 50 MHz signal is centered,
then adjust the VARIABLE Gain control for a signal
amplitude of 6.3 divisions.
f. Switch the RF Attenuator to 20 dB to add 10 dB of
attenuation, and note that the signal amplitude decreases
Operating Instructions-71-13
USING THE ANALYZER
to approximately 2 divisions fora ratio change of 3.16 (this
is equivalent to 10 dB in LIN mode) .
1. Signal Application
g . Return the RF Attenuator to 0 dB, the VARIABLE
Gain control to CAL. The signal amplitude should return
to full screen and the REFERENCE LEVEL should indicate
-30 dBm.
The RF INput impedance to the 71-13 is 50 O. At high
frequencies, impedance mismatches between the RF
INput and the signal source can cause reflections in the
transmission line and degrade instrument performance.
Flatness, sensitivity, spurious response, etc., are all
affected . To reduce mismatch, use good quality 50 f2
coaxial cable to connect the signal source to the RF INput
and keep the cable as short as possible . Cable losses
become excessive above frequencies of 1 GHz .
6. Adjust Contrast and Check Baseline Clipper
Operation
NOTE
Avoid applying high level signals (above -30 dBm) to
the 1st mixer of the 71-13. High level signals overload the
mixer and may produce spurious signals . A conversion
chart shown in Fig . 2-5 will aid in determining inputsignal
level, in dBm,pV, and uW, from a voltage or power source .
The contrast ratio between the clipped portion of the
display baseline and the rest of the display is
affected by the sweep rate, frequency span, resolution, and ambient light.
a. With the BASELINE CLIPPER control set midrange,
adjust the CONTRAST control for the desired ratio
between the clipped or subdued portion and the rest of the
display. Usually the contrast is adjusted so the clipped
baseline portion is just visible.
The input maximum power level to the RFAttenuator
is 1 watt average or 200 watts peak. When the RF
input signals are riding on a do potential, use the do
block (Part No . 015-0221-00), to prevent the do from
reaching the 1st mixer. When the signal source is
75 n and you are using the 75 to 50 0 minimum loss
attenuator, a do block is not required because one is
incorporated in the attenuator .
b. Adjust the BASELINE CLIPPER control so the
baseline is subdued. If there is excessive noise it may be
desirable to clip noise level as well .
NORMAL OPERATING
RANGE
~100pv
1Av
10'av
OdBm -130d13m -120dBm -110d13m -100dBm -90dBm
11W
NOTE :
11W
0.001pw
0.01pw
0.1PW
1 .0pw
100uv
1mv
~10mv
-80dBm
-70dBm
-60dBm
-50dBm
-40dBm
-30dBm
10pw
100PW
1 .0nW
10nW
1OOnW
1 .OgW
100mv
-20dBm
-10dBm
10JAW
100kW
OdB
Volts RMS . . . multiply by
2.8 for peak-to-peak .
0 dBm 1 milliwatt
Fig. 2-5. Volts-dBm-Watts conversion chart for 50 t2 Impedance.
2-9
Operating Instructions-71-13
Spurious response, caused by signal overload into the
1st mixer, can be minimized if the signal amplitude is kept
within the graticule limits . A recommended procedure is to
adjust the Gain selector for some baseline noise on the
display, then increase the RF Attenuator setting until the
strongest signals are within the graticule limits . If this does
not bring these signals within limits, add external
attenuators .
The 71-13 can be used with a 75 f2 signal source by
using a 75 f2 to 50 f2 minimum loss attenuator . This
attenuator is available as an optional accessory (refer to
the optional accessories list in the catalog or Accessory
page in the manual for ordering information) . Sensitivity
and power levels are often rated in dBm (dB with reference
to 1 mW regardless of impedance) . Sensitivity and power
levels for 75 fl systems are usually rated in dBmV (dB with
reference to 1 mV across 75 f2) . Fig . 2-6 is a circuit
diagram of a suitable matching pad for this purpose. The
conversion from dBmV to dBm, and dBm (75 0) to dBm
(50 0) through the matching attenuators, is shown in
Fig . 2-7 and described as follows:
[1] (dBmV, into 75 f2) - (dBm, at 50 f2 end) =54.46 dB
ordBmV=54.5 dB+dBm . Forexample :-30 [email protected] ()
= 54 .5 dB + (-30 dBm) or + 24 .5 dBmV at the 75 f2 input .
[31
[21
dBm
dBMV
(75 s2)
(5092)
INE NOME
[11
dBmV
(75 s2)
+87 M
+67
+47
EMIMMOMME
No MEMNON,
MEEMERNME
EMEMOMMIN
i
MPAAVMMMIM M
0
-107 -100
-80
-60
-40
dBm (50 92)
-104 .7
-20
Fig. 2-7. Graph to Illustrate relationship between dBm, dBmV,
and dBMV .
[21 dBm @ 75 f1 = dBm @ 50 f1 + 5.72 dB . For
example : -30 dBm @ 50 f2 + 5.72 dB = 24 dBm @ 75 0 .
bandwidth, sweep speed, frequency span, and incidental
FM . The frequency span and sweep time are adjusted for
minimum bandwidth to a cw signal . Theoretically, resolution and resolution bandwidth become synonymous at
very long sweep times.
[3] For some applications you may wish to know the
relationship between dBm and dBNV . For 50 f2 systems
dB,uV = (dBm) + 107 dB .
Resolution bandwidth is measured and specified for
the 71-13 as the bandwidth (separation) at the 6 dB down
point on the signal .
As the analyzer sweep rate is increased, the signal
amplitude will decrease and bandwidth will increase,
signifying that both sensitivity and resolution have been
degraded .
The best resolution with no video filter, for a given
frequency span and sweep time is expressed as :
-Frequency Span (in kHz)
Ro _
Sweep Time (in ms)
Fig. 2-6. Circuit of a 75-0 to 50-f) matching pad (ac coupled) .
2. Resolution, Sensitivity, and Frequency Span
Resolution is the ability of a spectrum analyzer to
discretely display adjacent signals within a frequency
span . This resolution ability is a function of analyzer
2- 1 0
Bandwidth determines both noise level and the resolution capability of the analyzer . As the bandwidth
decreases, the signal-to-noise level and, therefore, sensitivity increases. Maximum sensitivity, therefore, is obtained at the higher resolution settings .
The frequency span is symmetrical about the center
frequency. The frequency span to be used, depends on the
application . Wide frequency spans are used to monitor a
O
Operating Instructions-71-13
frequenc y spectru m for spurious signals, check harmonic
distortion, etc. Narrow frequency spans are used to
identify a particular signal ; check its characteristics such
as modulation, bandwidth, etc.
Again, the UNCAL indicator will light if thesweepspeed is
too fast for the video filtering, RESOLUTION and FREQ
SPAN/DIV selected .
When wide frequency spans are displayed, sweep rate
is usually increased to eliminate flicker; this requires the
use of wide resolution bandwidths . When narrowfrequency spans are used, high resolution capability is usually
desired and slow sweep speeds are required .
The FREQ SPAN/DIV and RESOLUTION selectors for
the 71-13 are normally coupled together to optimimize
resolution for the frequency span selected ; however,
either can be independently set by pulling out the "PULL
TO UNLOCK" sleeve around the FREQ SPAN/DIV selector.
An UNCAL indicator will light when the sweep time is
too fast for an amplitude calibrated display. Sweep speed
should be reduced to maintain a calibrated reference level
if the UNCAL indicator lights .
11rMM21MOME
(A)
I
"""
IM distortion obscured by noise. (1 MHz + 94 MHz)
For pulsed applications, the resolution bandwidth of
the analyzer should be on the order of 1/10 the side lobe
frequency width, or the reciprocal of the pulse width, in
order to ensure adequate resolution . The RESOLUTION
selector is usually set, after the sweep rate has been
adjusted, for optimum main lobe detail .
3. Gain Desensitization Near 0 Hz
If the Gain selector is set for a REFERENCE LEVEL that
is -50 dBm or more (e .g ., -60 dBm) with the RF
Attenuator at 0 dB, a decrease insensitivity will be noticed
below 1 MHz. This effect is caused by the 0 Hz response
overdriving the list IF amplifier. If you are operating
between 0 Hz and 2 MHz, do not set the Gain selector in
this region .
4. Using the Video Filter
The video filter is used for effective averaging of
distributed signals, such as noise, and high frequency
components on the display (see Fig . 2-8) . When signals
are closely spaced, the filter may be useful in reducing
modulation between the two signals so they can be more
easily analyzed . The filters can also be used to average the
envelope of pulsed RF spectra that has a relatively high
PRF (pulse repetition frequency) ; however, because the
filter is basically an integrating circuit, low PRF signals
produce poor results.
The use of the video filter may require a reduction in
sweep speed in order to maintain a calibrated display .
(B) Display with VIDEO FILTER added to average the
noise level.
Fig. 2-8. Integrating the display with the VIDEO FILTER .
5 . Selecting Sweep Rate
Because the FREQ SPAN changes the resolution and
sensitivity, the sweep rate must be decreased as the
frequency span and resolution bandwidth are decreased,
or when the UNCAL indicator lights . When the FREQ
SPAN is reduced to 0, the analyzer functions as a fixed
tuned receiver . The analyzer now displays time domain
characteristics of the signal, within the bandwidth
capabilities of the analyzer . Sweep Time/Div can now be
used to examine or analyze such characteristics as
modulation pattern, pulsed repetition rates, etc.
2- 1 1
Operating Instructions-71,13
NOTE
The RESOLUTION bandwidth should be maximum
for time domain analysis.
6. Triggering the Display
The sweep trigger source is usually switched to the
FREE RUN mode for normal spectrum displays ; however,
it may be desirable or necessary to trigger the display
when the event is time related to some source, or when the
frequency span has been reduced to zero and a time
domain analysis is performed .
7. Manual Scan of the Spectrum
This position is used to examine a particular point or
portion of the display, such as one of the null points of a
frequency modulation spectrum .
a. Calibrate the sweep span with the TIME/DIV selector in one of the scan positions as previously described,
then switch to the MANUAL position .
b. Use the MANUAL SCAN control to scan the
selected frequency spectrum .
The sweep can be triggered from the vertical or video
signal from either vertical plug-in compartment, from the
power line voltage, or from an external source. Trigger
slope for any mode can be + or -; the triggering level is
adjustable over the full range of a displayed signal when
using INTernal trigger source, over a 10 V range of an
external signal when using EXTernal source, and over the
peak-to-peak range of the line signal when using LINE .
8. Using an External Sweep Source
A signal source is required to sweep the analyzer
externally. A voltage ramp from 0 V to 10 V f1 V will
sweep the analyzer through its full span . 0 V corresponds
to 0 Hz and 10 V to the high frequency end of the selected
span. Input impedance is approximately 12 kC2 for an
external sweep signal.
In the NORM triggering mode, the display is triggered
when the triggering signal source is within specifications .
If the triggering signal is absent or outside of
specifications, the sweep recurs automatically to provide
a display baseline .
Before switching to external operation, calibrate the
sweep span using the internal sweep and the 50 MHz
calibrator signal as described under Operational Check .
Switch the TIME/DIV selector to its EXT position and
apply the external voltage to the EXT IN HORIZ/TRIG
jack. Adjust the upper end of the voltage (10 V) until the
analyzer sweep span is calibrated .
The amplitude of triggering signal that is required to
trigger the sweep depends on the sweep mode selected .
The internal signal is ac coupled ; the line and external
signals are do coupled . Trigger sensitivities are:
1) <0 .5 division of signal (peak-to-peak) and <0.5 volt
(peak-to-peak) of external signal for NORM mode .
2) <0 .5 division of signal (peak-to-peak) and <0.5 volt
(peak-topeak) of external signal for SGL SWP mode.
Maximum safe trigger input signal level to the EXT
INput is 50 volts (dc + peak ac) .
In the FREE RUN state, the sweep will not synchronize
with any input trigger signal .
When the SGL SWP button is depressed, the sweep will
run after the adjoining button is depressed . During the
sweep cycle, the activating button lights to indicate that
the sweep is running. This feature is useful when
photographing displays at slow sweep rates . The activating button does not arm the trigger circuit like some
time base units .
When triggering on pulsed spectra, it may be necessary
to fine tune the sweep start away from a null point to
trigger the display.
2-1 2
NOTE
The frequency deviation across the selected span is
a linear function (within 20%)of the inputvoltage, so
+5 V do should tune the analyzer to the center of the
selected frequency span.
9. External Trigger Operation
This procedure is applicable when an external trigger
source, such as a pulse generator or modulator, is used to
trigger the display so it can be synchronized to an event
(e.g ., measuring PRF of a radar signal) .
a. Apply the trigger signal (>0.5 V peak) to the EXT IN
HORIZ/TRIG jack of the 71-13 . Switch the TRIGGERING
SOURCE to EXT and the TIME/DIV selectorto thedesired
sweep rate.
b . Adjust the triggering SLOPE and LEVEL for the
desired triggering point.
c. If time domain information is desired, reduce the
FREQ SPAN/DIV to 0 and set the RESOLUTION to 3 MHz.
Operating Instructions-71
.13
--,
The analyzer is now triggered by the external source so
the display sweep rate can be contolled externally .
10 . Using the CAL OUT Signal Reference for
Accurate Frequency and Amplitude Measurements
The accuracy of frequency measurements may be
improved by using harmonics of the crystal controlled
Calibrator . The Calibrator accuracy is within 0.01% .
Frequency measurements within 2 MHz are possible by
using either of the two methods described below.
Measuring the Frequency Span between a Calibrator
Marker and the Signal to Obtain an Absolute Frequency
Measurement
a. Tune the signal to the center graticule line, approaching this point from the low frequency side of the
display. Couple the FREQ SPAN/DIV and RESOLUTION
selectors together and open up the display to obtain an
accurate setting, by reducing the FREQ SPAN/DIV to
5 MHz and increasing RESOLUTION to .3 MHz. Adjust
SWP CAL, if necessary, to calibrate the display for
10 divisions between the 50 MHz calibration markers.
(Remember to approach the center point from the low
frequency side .)
b. Connect the CAL OUT signal and the signal source
through a BNC "T" connector to the RF INput so both
signal and markers are displayed .
c . Measure the frequency span between the signal and
the nearest 50 MHz marker . (Frequency span is
5 MHz/Div .)
d . Add or subtract the frequency span to the respective
marker to obtain thesignal frequency. Since the maximum
frequency span between the signal and marker is 25 MHz
f5%, marker accuracy is 0 .01% and human observation
error is approximately 1/2 a minor division or0.5 MHz. The
accuracy using this method is within 2 MHz.
Measuring the Frequency after the Frequency Readout
Correction Factor Has Been Established
a . As described for the frequency span method, tune
the signal to the graticule centerline, opening the display
to 5 MHz/Div to obtain an accurate setting. Tune the
signal to the center from the low frequency side .
b. Note the frequency readout (e .g ., 1002 MHz) .
c. Apply the CAL OUT signal to the RF INput and tune
the nearest 50 MHz marker to the graticule centerline .
d . Set the frequency readout, with the CAL adjustment
to read the exact frequency (e .g ., 1000 MHz) .
e . Retune to the unknown signal, approaching it from
the low side and note the frequency readout.
Measuring Absolute Signal Levels
Since the top of the graticule is a calibrated
REFERENCE LEVEL and the graticule is calibrated in
dB/DIV, as described in the Preliminary Front Panel
Calibration procedure, at the beginning of this section, it is
easy to measure the absolute level of most signals.
a. Calibrate the graticule as previously described in
step 4 of the Operational Check procedure. Ensure that
the REF VARiable (gain) control is in its CAL detent .
b . Connect the signal source to the RF INput, as
described under Signal Application . Switch to the
10 dB/DIV or 2 dB/DIV display mode .
NOTE
For maximum accuracy, use the same cable that was
used to calibrate the REFERENCE LEVEL and use
the 2 dB/DIV display mode .
c. Select a REFERENCE LEVEL with the RF Attenuator
and gain selector to bring the signal, to be measured,
within the screen or graticule window .
NOTE
If you are operating in the 10 dB/DIV mode, thegain
selector must be within the blue sector.
d . The absolute signal level equals the number of dB
graticule divisions from the reference level (top of the
screen) to the signal reference (usually the signal peak)
plus the REFERENCE LEVEL readout in dBm. For example: A signal level 4.5 divisions below the top with a
REFERENCE LEVEL readout of-60 dBm, in the2 dB/DIV
display mode, is -60 dBm + (-9 dB) or -69 dBm . This
refers to the signal level at the RF INput connector. Add
the insertion loss of anyexternal attenuators and cables (if
they are used) between the signal source and the RF
INput.
NOTE
The maximum input level to the RF INput, for linear
operation, is -30 dBm with 0 dB RF attenuation ; or
+30 dBm with 60 dB of RF attenuation . Accurate
measurement of signals above this level can only be
performed if an external attenuator is used .
2-13
Operating Instructions-71-13
Accurate Signal Level Difference Measurements in dB
a. Using the 2 dB/DIV display mode, position the top
of the lowest amplitude signal to a reference line within the
graticule area with the REF VARiable or VERTICAL
POSITION controls . If display noise is excessive, use the
VIDEO FILTER and reduce the sweep speed to maintain
signal amplitude, or decrease the RESOLUTION
bandwidth .
b . Use the RF Attenuator selector to reduce the
amplitude of the larger signal until it iswithin thegraticule
area, and note the increased attenuator reading.
Figure 2-9 shows the performance of the 71-13 below
10 kHz. The center frequency is 2.5 kHz, with zero hertz
marker visible at the extreme left graticule. Two signals
were applied simultaneously to the input, one at 2.5 kHz
and one at 3 kHz .
Ivs
I
-30
i.
-30
-50
c . Measure the signal level from the reference line
established for the smallersignal (graticule is calibrated in
2 dB/DIV), then add the change in RF Attenuator reading
to obtain the difference level (in dB) between the two
signals.
Measuring Relative Signal Amplitude in LIN Display
Mode
The vertical scale on the spectrum analyzer graticule is
calibrated in dB for LOG display and in increments of 0.2
for the LIN display. Relative signal levels can be made by
adjusting the amplitude of one signal with the gain and
attenuator controls to 1 .0 division, then directly reading
from the graticule, the amplitude of the other signals as a
percentage of this reference.
Using the Analyzer Below 100 kHz
The sensitivity of the analyzer degrades about
0.3 dB/kHz below 100 kHz; for example, the sensitivity is
about -113 dBm at 50 kHz with 30 Hz resolution .
Reference level operation becomes limited to-50 dBm as
the center frequency approaches 1 kHz, because of the
LO energy that exists in the 1st IF pass-band .
Fig. 2-9 . Illustrating the dynamic range and performance at a
center frequency of 2.5 kHz .
APPLICATIONS
Applications for the spectrum analyzers, such as the
71-13, include: measuring intermodulation products, cross
modulation, radiation interference, modulation percentage, modulation index, absolute and relativesignal levels,
etc. A treatise on measurement and signal evaluation is
provided in the Tektronix Measurement Concept booklet,
"Spectrum Analyzer Measurement Theory" ; Part No . 0621334-00, and Spectrum Analysis and CATV Systems
brochure A2515 . If you desire assistance for a specific
application or current information on additional
applications, contact your local Tektronix Field Office or
representative .
Section 3-71
.13
PERFORMANCE CHECK
Introduction
This section consists of two parts ; an operational
checkout procedure for instrument familiarization and
incoming inspection, and a performance check that
verifies that the instrument meets specification
characteristics. The first part requires the minimum of test
equipment; the second part requires test equipment that
will serve as a standard to verify instrument specifications .
Performing this procedure will indicate if and what circuits
in the instrument need calibration . We recommend performing the checks as part of your routine maintenance
program.
OPERATIONAL PERFORMANCE
AND
INSTRUMENT FAMILIARIZATION
This portion of the section contains a sequence of
procedures that will check the operational performance of
the 71-13 . It provides an adequate incoming performance
inspection and a good familiarization of the instrument
operation . Because the 71-13 calibrator is a very accurate
signal source and the RF attenuator an accurate step
attenuator, they are used as the reference for this part of
the check. If you wish, their accuracy can be checked by
referring to the second part of this section .
Equipment Required
The following fixtures and equipment are required for
this part of the performance check. These are available
through your local Tektronix Field Office or representative .
The 1st and 2nd LO OUT ports must be terminated
into 50 f2 at all times. For optimum performance,
keep the termination caps in place when these ports
are not used .
2. Check the 10 dB/DIV and LIN Mode Calibration
a. Switch the RF Attenuator to 0 dB and turn the Gain
selector fully ccw, so the REFERENCE LEVEL readout is
-30 dBm. Ensure that the REF VARiable control is in its
CAL detent . Set the FREQ SPAN/DIV to 10 MHz and the
RESOLUTION bandwidth to 0.3 MHz.
b. Apply the Calibrator signal to the RF INput and tune
the fundamental 50 MHz signal to center screen .
c . Reduce the FREQ SPAN/DIV setting to 5 kHz and
the RESOLUTION bandwidth to 3 kHz, keeping the signal
centered on screen with the TUNING control.
d. Position the top of the signal to the top graticule line
with the VERTICAL POSITION control to establish a
reference level .
e. Increase the RF Attenuator settings in 10 dB increments, noting that the signal amplitude decreases 1
±0 .1 division between steps .
NOTE
1 . 80 dB of attenuation, in 20 dB increments : Four (4)
10X (20 dB) attenuators, Tektronix Part No . 011-0059-01 .
It may be easier to observe the change if the VIDEO
FILTER is switched in . If used, decrease the sweep
speed until the UNCAL indicator light goes out.
2. BNC to pin-jack adapter cable. Used to apply
signals to the EXT IN connectors . Tektronix Part No . 1751178-00.
f. Since the RF Attenuator range is 60 dB, the last
10 dB step of the 70 dB dynamic range may be checked as
follows:
1 . Preliminary Preparation
Perform the Preliminary Front Panel Setup Procedure
described in the Operating Instructions and calibrate the
71-13 sweep to the oscilloscope deflection sensitivity .
Adjust the contrast ratio between the clipped (subdued)
baseline and the remaining display.
(1) Return the RF Attenuator to 30 dB and add a
20 dB attenuator between the RF INput and CAL OUT
signal . Adjust the signal amplitude to some reference
line on the graticule with the REF VARiable control.
(2) Increase the RF Attenuator setting 20 dB and
note that the signal is still visible above the noise level .
Performance Check-71_13
The total deviation over the 70 dB dynamic range of the
display must not exceed 1 .5 dB or 0 .75 minor divisions .
g . Remove the 20 dB attenuator and again apply the
CAL OUT signal directly to the RF INput. Switch off the
VIDEO FILTER and set the RFAttenuatorto 10 dB . Set the
FREQ SPAN/DIV to 1 MHz and the RESOLUTION to
.3 MHz .
h . Change the display mode to LIN . Position the
baseline of the display on the bottom graticule line then
adjust the 50 MHz signal amplitude with the REF VARiable
control so it is 6.3 divisions .
i . Increase the RF Attenuation 10 dB by switching to
20 dB, and note that the signal amplitude decreases to 2.0
t0.6 division for an amplitude change ratio of 3.16:1,
t10%.
j . Return the REF VARiable control it its CAL detent
and the RF Attenuator to 0 dB.
3 . Check the Frequency Readout Accuracy
NOTE
Due to hysteresis in the tuning system (1st LO), the
accuracy of the frequency readout should be checked by approaching each check point from the same
direction (low to high). The FREQ SPAN/DIV is first
switched to MAX SPAN and the center frequency
tuned to 0000 before tuning to the desired check
point. If for any reason the direction of tuning is
reversed, this procedure must be repeated to establish the same point of reference on the hysteresis
loop,
a. Switch the display mode to 10 dB/DIV, the FREQ
SPAN/DIV to MAX SPAN and tune the CENTER FREQUENCY to 0000 . With the Calibrator signal applied to the
RF INput, decrease the FREQ SPAN/DIV to 1 MHz and
increase the CENTER FREQUENCY readout towards
50 MHz until the 50 MHz signal is centered on screen .
(The signals will move from right to left as the frequency is
increased .)
b . Adjust the front panel CAL for a CENTER FREQUENCY readout of 50 MHz.
c . Tune the CENTER FREQUENCY from low to high,
checking the accuracy of the readout in 50 MHz increments . Readout accuracy, when the signal is centered
on the screen, should be within f(5 MHz + 20% of the
FREQ SPAN/DIV) orwithin f5 MHz with a frequency span
of 1 MHz/DIV .
3-2
4. Check the Range of the REF VAR control, the
Range of the Gain Selector and Gain Accuracy of the
10 dB GAIN pushbutton . (Accuracy within
f1 dB/10 dB step . Variable range -10 dB.)
a . Switch the display mode to 10 dB/DIV, FREQ
SPAN/DIV to 0.5 MHz and the RESOLUTION bandwidth
to 30 kHz . Apply the CAL OUT signal to the RF INput and
tune the 50 MHz signal to the center of the screen then
decrease the FREQ SPAN/DIV to 50 kHz keeping the
signal centered with the TUNING control .
b. Switch the 30 kHz VIDEO FILTER in, turn the Gain
selector ccw and switch the RF Attenuator to 50 dB to
establish +20 dBm REFERENCE LEVEL.
c . Position the top of the signal at the 4th graticule line
(center screen) with the VERTICAL POSITION control .
d. Check the REF VAR control range by turning it fully
cw from its CAL detent . Gain increase should equal
approximately 10 dB or the signal amplitude should
increase 1 division . Return the REF VAR control to its CAL
detent.
e. Position the top of the 50 MHz signal at the 6th
graticule line from the reference level (top of graticule),
with the VERTICAL POSITION control .
f . Check the Gain selector accuracy of the three 10 dB
steps for the 10 dB/DIV display mode (blue sector) .
Accuracy between steps must equal 10 dB f1 dB .
g. Decrease the RF Attenuator to 40 dB so the
REFERENCE LEVEL is -20 dBm . Change the display
mode to 2 dB/DIV and position the top of the signal at the
5th graticule line from the reference, with the VERTICAL
POSITION control .
h. Increase the Gain selector setting 10 dB (one step) .
Check that the signal amplitude increases 10 dB f1 .0 dB
or 5 div t0.5 div.
i . Increase the RF Attenuator setting to 50 dB, and if
necessary, reposition the top of the signal to the 5th
graticule line from the reference . Check the accuracy of
the next 10 dB step of the Gain selector .
j . Increase the RF Attenuator setting to 60 dB and
check the accuracy of the next 10 dB step of the Gain
selector.
Performance Check-71-13
k. Return the RF Attenuator to 50 dB . Insert a 50 Q,
20 dB (10X) attenuator between the CAL OUT signal and
the RF INput.
-HddDm
I . Position the top of the 50 MHz signal at the 6th
graticule line from the reference with the VERTICAL
POSITION control and check the accuracy of the final
10 dB step of the Gain selector .
The signal level into the 1st mixer is now approximately -100 dBm.
"
' ~)KHZI RE5 ., ie
-zo
-30
a
m . Insert four (4) 20 dB attenuators, for a total of
80 dB, in series with the Calibrator signal and switch the
RF Attenuator to 0 dB so the REFERENCE LEVEL is
-100 dBm.
NOTE
1
-4s
`ro
(A)
Display without filter .
flEt
n . Reduce the FREQ SPAN/DIV to 0.2 kHz and the
RESOLUTION bandwidth to 30 Hz, keeping the 50 MHz
signal on screen with the TUNING control . Reduce the
sweep speed if necessary, until the UNCAL indicator light
goes out.
o. Position the top of the signal to a reference line with
the VERTICAL POSITION control (6th from the top is
usually the most convenient) .
p . Check for an additional 10 dB of gain when the
10 dB GAIN pushbutton is depressed .
q . Return the REFERENCE LEVEL to -30 dBm,
remove the 80 dB of attenuation and reconnect the
calibrator signal to the RF INput.
5. Check the Operation of the VIDEO FILTERS
The VIDEO FILTERS reduce or average the noise level
on the display. See Fig . 3-1 . Tune to one of the Calibrator
signals and check the operation of the filters with
RESOLUTION settings of 3 MHz and 3 kHz .
6. Check Sensitivity (-128 dBrn to -80 dBm,
depending on the resolution bandwidth)
NOTE
Sensitivity is measured in the LIN mode, and is
based on a signal amplitude that equals two times
the noise level.
dam
1.350 MH
t
J0 ° KHZ
PEKI_,
G
-su _
I
-ao
8
e
-so
(B) Same display with video filter . Note decrease in noise level.
Fig. 3-1. Video Filter operation.
a. Apply the CAL OUT signal to the RF INput and
switch the display mode to LIN . Uncouple the FREQ
SPAN/DIV selector from the RESOLUTION selector and
set the span for 2 MHz/DIV with a RESOLUTION of
3 MHz. Switch the RF Attenuatorto 0 dB and turn the Gain
selector fully ccw so the REFERNCE LEVEL readout
equals -30 dBm.
b . Tune to the 50 MHz fundamental signal and position the baseline of the display on the bottom graticule
line . Verify that the signal amplitude is 8 divisions or
-30 dBm signal level .
c . Increase the RF Attenuator setting to 50 dB so the
signal level into the 1st mixer of the 71-13 is now -80 dBm
(-30 dBm calibrator signal reduced 50 dB by the RF
Attenuator) .
3-3
Performance Check-7L13
d. Measure the instrument sensitivity (at 50 MHz) with
a resolution bandwidth of 3 MHz as follows:
(1) Adjust the Gain selector and REF VARiable
control settings for a noise level of 1 divison, in the LIN
display mode . Switch the 300 Hz VIDEO FILTER in, to
average the noise level . Decrease the sweep speed if
the UNCAL indicator lights .
(2) Compare the signal amplitude to the noise level .
Signal amplitude must equal or exceed 2X the noise
level (see Fig . 3-2A) .
e. Disconnect the CAL OUT signal to the RF INput,
return the REF VAR to its CAL detent and switch the RF
Attenuator to 0 dB . Set the Gain selector, if necessary, so
the REFERNCE LEVEL reads -60 dBm, then switch the
display mode to 10 dB/DIV .
f. Note or check the average noise level over the
20 MHz span . Noise level should be down 20 dB or more
from the 60 dBm REFERENCE LEVEL (2nd graticule line
from the top) .
Since
sensitivity is a measure of signal-to-noise
__
amplitude [(S + N], the noise floor is indicative of the
sensitivity value. This was verified in step d; therefore, the
average noise level should appear within or below the
specified sensitivity level (see Fig . 3-2B) .
Noise level set by Gain
controls to 1 .0 division .
(A) Check sensitivity at 50 MHz, with 3 MHz resolution . Signal
input level -30 dBm, RF attenuation 50 dB for an input
level, to the 1st mixer, of -80 dBm .
REFERENCE
LEVEL
7_e_T_.__"". I.. . __T
. .I _ I
Sensitivity
level
is
90
dBm
. Note :
I
Noise level moves up the screen as
the Gain is increased, because the _
top of the screen is the reference
level .
NOTE
Because the gain and noise floor of the display are
referenced to the top line of the graticule, the noise
floor may shift with Gain selector changes.
g . Switch the display to LIN mode, turn the Gain
selector fully ccw and the REF VAR control to is CAL
detent . Position the base of the display on the bottom
graticule line then switch the display mode to 10 dB/DIV .
h . Switch the RF Attenuator to 0 dB and increase the
Gain selector setting for a REFERENCE LEVEL readout of
-60 dBm (Gain selector must be in the blue sector) .
i. Reduce the FREQ SPAN/DIV to 1 MHz and the
RESOLUTION bandwidth to .3 MHz. Note the average
noise level below -60 dBm . Sensitivity for a resolution
bandwidth of 0.3 MHz must equal or exceed -90 dBm
(noise floor should be 30 dB below the reference level, or
below the 3rd graticule line from the top) .
3-4
(B) Average noise level, below the reference
sensitivity .
level is the
Fig . 3-2 . Measuring sensitivity .
j . Decrease the FREQ SPAN/DIV to 10 kHz and the
RESOLUTION bandwidth to 30 kHz. The noise floor must
be below the 4th graticule line or -100 dBm (-60 dBm +
40 dB) .
k. Decrease the RESOLUTION bandwidth to 3 kHz
and again note the noise level . Noise floor must be below
the 5th graticule line from the reference, or -110 dBm. It
may be desirable to switch in 10 Hz of video filtering by
depressing both VIDEO FILTER pushbuttons. Reducethe
sweep speed if the UNCAL indicator lights .
I . Decrease the RESOLUTION bandwidth to 300 Hz
and again note the noise level. The average noise level
must be below the 6th graticule line for a sensitivity that
equals or exceeds -120 dBm .
Performance Check-71-13
m. Decrease the RESOLUTION bandwidth to 30 Hz
and the FREQ SPAN/DIV to 0.5 kHz. Note that the noise
floor is 6.8 or more divisions below the reference level fora
sensitivity of -128 dBm or better .
NOTE
(2) Decrease the sweep speed if the UNCAL indicator lights . Note the spurious response amplitude
and verify that it does not exceed specifications .
f. Return the FREQ SPAN/DIV and RESOLUTION
selectors to their original settings (step. d) .
If the Gain selector is setso the REFERENCE LEVEL
is -50 dBm or more (e .g ., -60 dBm) with the RF
Attenuator at 0 dB, a decrease in sensitivity will be
noticed below 1 MHz. This effect or desensitization,
is caused by the 0 Hz response overdriving the 1st IF
amplifier. If you are operating in this frequency
range do not set the Gain selector this high .
8. Check Resolution Bandwidths and Shape Factor. (Bandwidth 3 MHz to 30 Hz within 20% in
decade steps; shape factor 4:1 to 300 Hz except
3 MHz resolution . Maximum bandwidth 60 dB
down, with 3 MHz resolution is 13 MHz. Shape
factor for 30 Hz is 12 :1)
7. Check for Spurious Signals from Internal
Sources (Residual Responses) . (,< -100 dBm,
referred to the RF INput)
a. Apply the Calibrator signal to the RF INput and set
the RF Attenuator to 0 dB . Turn the Gain selector fully ccw
for a REFERENCE LEVEL of -30 dBm .
a. Remove any signal connected to the RF INput so it is
free of signals from any external source . Switch the RF
Attenuator to 30 dB to further isolate the 1st mixer from
the input.
b. Tune the 50 MHz marker to the center of the screen,
set the FREQ SPAN/DIV to 1 MHz, and the RESOULITON
bandwidth to 3 MHz .
b. Switch out the VIDEO FILTER, turn the Gain
selector fully ccw and ensure that the REF VARiable
control is in its CAL detent . The REFERENCE LEVEL will
now read 0 dBm . The signal level at the 1st mixer of the
71-13 however represents -30 dBm, because the RF
Attenuator subtracts an additional 30 dB .
c. Set the FREQ SPAN/DIV to 1 MHz and the
RESOLUTION bandwidth to 30 kHz . Switch the TIME/DIV
to 50 ms or less so the UNCAL indicator is not lighted .
d. Switch to the 2 dB/DIV display mode, verify that the
trace is on the bottom graticule line, then switch the
display mode to 10 dB/DIV . The dynamic range of the
graticule is now a calibrated 10 dB/DIV, with the top line
representing -30 dBm into the 1st mixer as described in
step b.
e. Tune slowly across the frequency band (0 to
1 .8 GHz) checking for spurious signals. The amplitude of
any spurious signal must not exceed -100 dBm (signals
above the 7th graticule line from the top) . NOTE : Subtract
2 dB for noise which will be riding on top of the signal . If
the spur is marginal (within 3 dB of specifications) and
you desire to check its amplitude more accurately,
proceed as follows:
(1) Decrease the FREQ SPAN/DIV to 50 kHz or less
and the RESOLUTION bandwidth to 3 kHz. (This will
decrease the noise with respect to the signal
amplitude.) Keep the signal centered on screen with the
TUNING control as the FREQ SPAN is decreased .
O
c. Switch the display mode to 2 dB/DIV and adjust the
REF VARiable control if necessary, for a full screen
display.
NOTE
Ensure that the sweep rate is set so the UNCAL light
is out and the baseline of the display is on the bottom
graticule line .
d . Check the bandwidth of the signal at the 6 dB down
level (see Fig. 3-3A). Bandwidth must equal 3 MHz
±600 kHz .
e. Switch the display mode to 10 dB/DIV and the
300 Hz VIDEO FILTER in . Switch the FREQ SPAN/DIV to
2 MHz and check the shaper factor (see Fig. 3-38) .
f. Return the display mode to 2 dB/DIV, decrease the
FREQ SPAN/DIV to .1 MHz and the RESOLUTION
bandwidth to .3 MHz. Keep the signal centered on screen
with the TUNING control as the FREQ SPAN is decreased.
g . Check the bandwidth at the 6 dB down level .
Bandwidth must equal 300 kHz ±60 kHz.
h. Switch the FREQ SPAN/DIV to .2 MHz, display
mode to 10 dB/DIV, and check the shape factor as
described in step e.
3- 5
Performance Check-7L13
i. Reduce the FREQ SPAN/DIV to 10 kHz, the
RESOLUTION bandwidth to 30 kHz, and the display mode
to 2 dB/DIV .
REF
,,
OB1
~Jddotool
MH
J
JMHZ Its'
_Eo
j. Check the bandwidth . Bandwidth must equal 30 kHz
±6 kHz.
-20
7
~
6 dB do
Lo
-30
Bandwidth
r2 .6 MHz
k. Reduce the FREQ SPAN/DIV to .2 kHz and the
RESOLUTION bandwidth to 300 Hz . Center the display
with the TUNING control if necessary.
-40
r~r~r~r~rr~~rr~~rr
(A)
I. Check the bandwidth of the response at the -6 dB
level . Bandwidth must equal 300 Hz ±60 Hz .
Display mode LIN. Bandwidth measured at 6 dB down
level. Resolution 3 MHz. Frequency Span 1 MHz/DIV.
'I
Edsm
-6 dB
e,
HZ
CO) 50
m . Switch the display mode to 10 dB/DIV, depress the
30 kHz VIDEO FILTER pushbutton to increase the filtering
to 10 Hz . Reduce the sweep speed to 2 s/Div to maintain a
calibrated display. Measure the response shape factor .
;MHz
Shape factc r
I
12 .6 = 4.E
2
.6
z
n . Reduce the RESOLUTION to 30 Hz and change the
display mode to 2 dB/DIV . Check the bandwidth at the
-6 dB (half screen) level . Bandwidth must equal 30 Hz
±6 Hz .
_40
6
T
man
-60 dB
(B) Display mode 10 dB/DIV . Shape factor is ratio of bandwidth at -60 dB to -6 dB levels .
4
2
,_
i .o
e
t
-
-JC deM,
REF
Hz
30 Hz
}
.
n
Shape Facto r
360
3
0 =
12 :'
_
.E
MMM
6
(C) Shape factor of 12 :1 with 30 Hz resolution .
Fig. 3-3. Three displays to illustrate how to measure bandwidth
and shape factor.
3-6
o . Switch the display mode to 10 dB/DIV and measure
the shape factor . Shape factor for 30 Hz resolution must
equal 12 :1 or better (see Fig. 3-3C) .
9. Check Incidental Wing . (<10 Hz for any internal sweep rate, when phase locked ; <20 kHz without
phase lock) .
NOTE
A storage mainframe is
FM'ing .
desirable when
measuring
a. With the Calibrator signal applied to the RF INput,
switch the RF Attenuator to 0 dB and the Gain fully ccw.
Switch the FREQ SPAN/DIV to0 .1 MHz, RESOLUTION to
30 kHz, display mode to LIN, VIDEO FILTERS off, sweep
rate to 20 ms/Div, and the AUTO PHASE LOCKED mode
OFF.
b. Tune the CENTER FREQUENCY to one of the
50 MHz markers, then adjust the Gain selector or REF VAR
control for a fully screen display. Decrease the FREQ
SPAN/DIV to 10 kHz and the RESOLUTION bandwidth to
3 kHz.
c. Check the FM'ing of the displayed marker . FM'ing
must not exceed 20 kHz (2 .0 div) . Fig . 3-4 illustrates one
method of measuring FM'ing .
Performance Check-71_13
-J df~m
, ;-O05io ` MH
JO #4Z bES
HEr
-ID
I
I
-
Power line frequencY
ands down more
40 dB from th e
. .1 reference level
J
Fig . 3-4 . Measuring incidental Wing .
d. Switch the AUTO PHASE LOCKED mode on and
tune the signal to center screen . Decrease the FREQ
SPAN/DIV to .2 kHz and the RESOLUTION to 30 Hz .
Decrease the sweep rate to 1 s/Div or until the UNCAL
light goes out and add both VIDEO FILTERS so filter
bandwidth is 10 Hz . Switch the oscilloscope mainframe to
store mode with auto erase, if available.
e. Switch the display mode to 10 dB/DIV . Check the
Wing for each sweep. 10 Hz is only a trace width at
200 Hz/DIV ; however, Wing can be checked by noting
that the line frequency sidebands are down at least 40 dB
from the reference level . See Fig . 3-5.
10 . Check Sweep Circuit Operation with the
TIME/DIV Selector in the MANUAL and OFF
Positions
a. Switch the TIME/DIV to the MANUAL position and
rotate the MANUAL SCAN control through its range . Note
that the crt beam scans the full 10 divison graticule width.
b. Switch the selector to the OFF position and note
that the crt beam is now centered on the screen .
c. Return the TIME/DIV selector to 50 ms position for
normal operation .
This completes the verification of the major
characteristics of the 71-13 . The remaining characteristics
have indicated by reliability tests that they can be
accepted without further checks ; however, the procedure
to verify these characteristics is contained in the second
part of this section . These checks require elaborate test
equipment. If you wish to verify the remaining
characteristics, continue to the next part of this section .
w
Fig. 3-5. Illustration to show how Wing is measured with a
resolution bandwidth of 30 Hz .
PERFORMANCE CHECKS THAT
REQUIRE TEST EQUIPMENT
Introduction
The following procedures check the accuracy of the
71-13 calibrator and RF Attenuator, the display flatness,
intermodulation distortion, video output amplitude, sweep
triggering operation, sweep Time/Div accuracy, and external sweep operation . It does not include any internal
adjustment or checks . If the instrument fails to meet a
specified performance requirement, the adjustment
procedure for the related circuits will be found under a
similar title in the Calibration Procedure, Section 4.
History Information
The instrument and manual are continually evaluated
and updated . Circuits as well as procedures are modified .
Procedures and information, applicable to earlier instruments, are included as deviations within these steps or
as subparts of the steps . These are indicated in the
procedure .
Equipment Required and Recommended
The following test equipment and fixtures are
recommended to perform this portion of the performance
check . Test equipment specifications arethe minimum for
accurate checks . Substitute equipment must meet or
exceed these specifications .
Special calibration fixtures are used where necessary
to facilitate the procedure. These are available from
Tektronix, Inc., and may be ordered through your local
Tektronix Field Office or representative .
3-7
Performance Check-7L13
When equipment is required to check or verify close
tolerance specifications, a compromise is made . Any
compromise is indicated by a footnote to the equipment
list, along with a statement that the high tolerance
specification is not checked because of the compromise .
TABLE 3-1
EQUIPMENT LIST
NOTE
This equipment is also required to recalibrate the instrument .
EQUIPMENT OR TEST
FIXTURE
CHARACTERISTICS
REQUIRED
TYPE OR MODEL
RECOMMENDED
7000-Series Storage or
Variable Persistence
Oscilloscope with Readout
Frequency bandwidth: 50 MHz
Tektronix 7313, 7613 mainframe
Test Oscilloscope
Vertical sensitivity : 50 mV/Div
to 5 V/Div
Any Tektronix 7000-Series Oscilloscope with plug-in units for
a real time display
Bandwidth : 50 MHz
Time Mark Generator
Marker outputs : 1 s to 1 /is
Accuracy : 0.001%
Pulse Generator
Pulse period : 40 ps
Pulse duration : 0.2 ps
Tektronix 2901 with Harmonic
Modulator, Part No . 067-0640-00
(Used to check TIME/DIV and
FRED SPAN/DIV accuracies)
Tektronix 2101 Pulse Generator (Used to check
PULSE STRETCHER)
Pulse amplutude: 0.5 V P-P
Digital Counter
To 50 MHz
Tektronix 7D14 Digital
Counter with a readout 7000Series Oscilloscope and
Vertical Amplifier Unit .
(Used to check 50 MHz
accuracy of the Calibrator)
Signal Generators
Frequency range: 10 Hz
to 1 .8 GHz.
Used to check intermodulation,
triggering, and flatness
characteristics
Output amplitude: 0 V to 5 V
(10 Hz to 10 MHz) ; -110 dBm
to 0 dBm (10 MHz to 1 .8 GHz) .
Output variable and calibrated
in dBm from 10 MHz to 1 .8 GHz.
Accuracy f1 .0 dB .
LF
1 Hz to 1 MHz, output amplutide
at least 10 V peak . Output
impedance 50 f2 to 600 f2
General Radio Model 1310A or
Hewlett Packard Model 202C
HF
22 kHz to 10 MHz
Hewlett Packard Model 8651A
Performance Check-71-13
TABLE 3-1 (cont)
TYPE OR MODEL
RECOMMENDED
CHARACTERISTICS
REQUIRED
EQUIPMENT OR TEST
FIXTURE
VHF
10 MHz to 480 MHz
Hewlett Packard Model 608D
or 608E
UHF
450 MHz to 1230 MHz
and 800 MHz to 4500 MHz
Hewlett Packard Model 612A
and HP Model 8614A or 8614B
Measure -30 dBm within
±0 .1 dB . Filter must
have rolloff >40 dB
at 100 MHz.
General Microwave Model 454A ;
or Hewlett Packard Model 432A
-30 dBm, 50 MHz
Signal Source
Power source may be
calibrated by Power Meter.
Hewlett Packard Model 608D
or 608E
or
Vector Voltmeter'
Frequency: 50 MHz
Hewlett Packard Model 8405A
RG-58C/U
Tektronix Part No . 012-0076-00
Power Meter with 50 MHz
Low Pass Filter;
or
Two 18 inch 50 Q low
loss coaxial cables
BNC-to-BNC connectors
Two 10 :1 50 S2
Attenuators
Tektronix Part No. 011-0031-00
BNC "T" connector
Tektronix Part No . 103-0030-00
Pin-jack to BNC
Adapter cable;
20 inch
Signal application to the
EXT IN pin jacks or connect
an external device to the
VIDEO OUT jack
Tektronix Part No . 175-1178-00
'Three methods are described to check output power level of the Calibrator . Refer to this step in the procedure to determine
which test equipment you desire.
1 . Check the Calibrator Frequency
a . Frequency check: (Accuracy 50 MHz ±0 .01%)
The frequency of the calibrator may be checked by an
accurate frequency counter, such as Tektronix 7D14
Digital Counter Plug-In Unit with a readout 7000-Series
oscillosocope and a 50 MHz vertical plug-in unit . The
Vertical Amplifier (e .g ., 7A15) is used to amplify the
-30 dBm 50 MHz signal to approximately 30 mV peak-topeak to trigger the 7D14 . No procedure for this check is
provided because the CAL OUT signal frequency can be
measured by connecting through an amplifier unit to the
input of the counter .
2. Check
±0 .3 dB)
Calibrator
Output
Level
(-30 dBrn
Three procedures are given : Vector Voltmeter method,
Power Meter method, and the use of an accurate-30 dBm
source . The output of the calibrator contains harmonics;
therefore, direct measurement is not possible .
a. Vector Voltmeter Method (Hewlett Packard Model
8405A Vector Voltmeter)
(1) Terminate the "A" probe with a BNC 50 0
feedthrough termination and connect the probe,
through the termination, to the CAL OUT connector on
the 71-13.
3-9
Performance Check-711.13
(2) Switch the Vector Voltmeter frequency to
50 MHz .
(5) If necessary, adjust the output of the calibrator
as described in the Vector Voltmeter method, for
-30 dBm .
(3) Check for an RMS reading between 6.85 mV to
7.3 mV (-30 dBm is 7.07 mV-RMS, into 50 C2) . If
output is out of specification refer to Calibrator Output
adjustment in the Calibration Procedure .
3. Check RF Attenuator Accuracy (Within f0.2 dB
+1% of the dB readout whichever is greater .)
b. Accurate Power Meter (within 0 .1 dB) and a 50 MHz
Low Pass Filter with 40 dB or more rolloff at 100 MHz
(General Microwave Power Meter Model 454A, or Hewlett
Packard Model 432A Power Meter) .
NOTE
The insertion loss, of the filter, must be accounted
for to an accuracy of 0.1 dB
(1) Connect the power meter through the filter to
the CAL OUT connector .
(2) Measure the output level.
c. Using a -30 dBm Signal Source to check the
Output by Signal Substitution Method .
NOTE
The power meters suggested for the second method
can be used to verify the signal source output level.
(1) Set the FREQ SPAN/DIV to 0.5 MHz and the
RESOLUTION bandwidth to .3 MHz . Switch the RF
Attenuator to 10 dB and the Gain selector fully ccw .
Push the 2 dB/DIV LOG display button .
(2) Apply 50 MHz, from the calibrated - dBm
source, to the RF INput of the 71_13 and tune the signal
to the graticule center . Adjust the REF VAR control to
position the top of the signal to some reference line
(2nd or 3rd from the top) .
(3) Disconnect the -30 dBm reference signal, then
apply the 71_13 CAL OUT signal to the RF INput
connector .
(4) Check-The displacement of the 71_13
calibrator 50 MHz signal level, from the reference
signal level must not exceed 110 .3 dB (0.75 minor
divisions with a 2 dB/DIV display mode) .
3- 1 0
NOTE
The RF Attenuator accuracy is checked at the
factory to ensure that it is within specifications. This
check will detect any component failure within the
attenuator but it will not check the tolerance
characteristics . If the exact attenuation error of the
selector is required, a reference attenuator,
calibrated by the user or manufacturer to more rigid
specifications than the 71_13 attenuator, must be
used.
a. Set the front panel controls and selectors as follows :
RF Attenuator
Gain
Display Mode
FREQ SPAN/DIV
RESOLUTION
Center Frequency
0 dB
ccw
LOG 2 dB/DIV
1 MHz
.3 MHz
200 MHz
b. Apply a -60 dBm, 200 MHz signal from the VHF
signal generator to the RF INput. Adjust the Gain selector
and REF VAR control fora signal amplitude of 4 divisions .
c . Check the RF Attenuator selector accuracy by
increasing the RF Attenuator setting in 10 dB increments,
and decreasing the Variable Attenuator setting (on the
VHF generator) 10 dB . The display amplitude should
remain at 4 divison f0.2 dB or 1% of the RF Attenuator
setting, whichever is greater .
4. Check Display Flatness
(Maximum amplitude variation over the 100 kHz to
1 .8 GHz frequency span is +1 dB, -2 dB, with respect to
the reference level established at 50 MHz .)
a. Set the front panel controls and selectors as follows :
CENTER FREQUENCY
Display Mode
RF Attenuator
Gain
FREQ SPAN/DIV
RESOLUTION
50 MHz
2 dB/DIV
10 dB
Fully ccw
MAX SPAN
3 MHz
Performance Check-71-13
b. Apply a -30 dBm, 50 MHz signal from the VHF
signal generator to the RF INput of the 71-13. Adjust the
REF VAR control for an amplitude of 6 divisions.
c . Check the flatness response, by tuning the signal
generator across its frequency range, maintaining a
constant output level, and noting signal amplitude
variations . Amplitude variations about the reference
6 division level should not exceed +1 dB, -2 dB .
d. Change to a UHF signal generator, then a SHF
signal generator as required, to check flatness over the
remaining frequency span of the 71_13.
freq
fl
f2
(A) Third (3rd) order intermodulation products.
NOTE
Cable losses become significant at frequencies
above 1 .0 GHz. Use RG-8C cable with BNC to N
adapter, or use very short cable lengths (< 1 foot)
between the signal generator and the 71-13 RF INput
connector. Impedance levels between the source
and RF INput are also important; refer to General
Operating Information; "Signal Application".
5. Check Intermodulatlon Distortion
(Third order distortion, 100 kHz-1 .8 GHz, is down
70 dB or more from two -30 dBm signals within any
frequency span . Second order distortion is down 70 dB or
more from two -40 dBm signals . Intermodulation
products, 1 kHz to 100 kHz, (3rd and 2nd) are down 50 dB
or more for the same input level. Fig . 3-6 illustrates third
and second order intermodulation products .)
a. Set the FREQUENCY SPAN to 1 MHz/Div and
RESOLUTION bandwidth to 30 kHz. Set the RF
Attenuator to 0 dB and the Gain selector fully ccw . The
REFERENCE LEVEL should read out -30 dBm. Switch
the 300 Hz VIDEO FILTER on and the display mode to
10 dB/DIV . Decrease the sweep speed until the UNCAL
indicator light goes out.
b. Apply two signals that are separated approximately
2 MHz, from the output of two 50Q signal sources,
through 10X attenuators (for isolation), then through a
BNC "T" connector, to the RF INput of the 71_13 . Fig. 3-7
illustrates this setup.
freq--P-f1
f2
(t3) Second 12nd) order intermodulation products (cross
modulation)
Fig . 3-6 . Intermodulatlon products (distortion) .
the level of the two signals, or below the 7th graticule line
from the top.
NOTE
Typically these intermodulation products are difficult to see. An alternate procedure, which will
average noise level, is to switch the 300 VIDEO
FILTER on and use a very slow sweep, looking for
any sidebands. If your oscilloscope has storage or
variable persistence, use the storage mode .
e. Tune the CENTER FREQUENCY towards 10 MHz
until the 0 Hz response is on screen .
f. Tune one signal generator frequency to approximately 500 kHz and adjust its output for a signal level
of -40 dBm or 1 division below the top of the graticule
(-30 dBm reference) .
NOTE
c. Adjust the output of both generators for -30 dBm
signal amplitude (full screen) .
Both generators must be connected as described in
step b.
d . Check the amount of third order intermodulation
distortion, by noting the amplitude of the IM products . The
amplitude of these IM products must be down 70 dB from
g. Tune the CENTER FREQUENCY of the 71-13 to the
frequency of the second signal generator and adjust the
generator output for a signal level of -40 dBm .
3- 1 1
Performance Check-71_13
7000 Series Oscilloscope
with 71-73 Spectrum Analyzer
10X attenuators
for isolation and
BNC "T" connector
Fig . 3-7 . Equipment setup and connections necessary to measure Intermodulation distortion .
NOTE
Refer to step b and have the frequency above
10 MHz .
h. Switch the Gain selector one step cw to shift the
-40 dBm signal to the REFERENCE LEVEL. Decrease the
FREQ SPAN/DIV to .2 MHz and the RESOLUTION
bandwidth to 3 kHz. Change the sweep rate to establish a
calibrated display (UNCAL indicator out) . The noise
amplitude should now equal about 1 division . The
dynamic range below the reference is now 70 dB .
i . Check-Second order intermodulation distortion
must not exceed 1 division, or 70 dB below the two
reference signals (see Fig. 3-7B).
j . Check-Intermodulation products from 1 kHz to
100 kHz, using the above procedures . IM products must
not exceed 50 dB below the reference signals .
6. Check PULSE STRETCHER Operation
(Pulse Stretcher should increase pulse falltime to at
least 2 .5 ps per vertical division .)
3- 1 2
Since the pulse stretcher responds only to pulsed
spectra, a pulse generator is used to make this
check. Use extreme care to ensure that the pulse
amplitude, into the RF INput of the 71_13, does not
exceed 100 mV (100 mV is approximately-3 dBm) .
a. Switch the display mode to LIN and the VIDEO
FILTER off. Set the TIME/DIV to 10 ms, the FREQ
SPAN/DIV to 2 MHz, and the RESOLUTION bandwidth to
300 kHz . Switch the RF Attenuator to 0 dB and the Gain
selector for a REFERENCE LEVEL readout of -30 dBm .
b . Tune the CENTER FREQUENCY to center the 0 Hz
response .
c. After ensuring that the pulse generator output is
below 1 V, apply its output through a 20 dB (10X) 50 Q
attenuator, to the RF INput of the 71_13 .
d . Set the generator pulse duration to .2 /is and its
period to 40 ps .
O
Performance Check-71_13
e . Adjust the oscilloscope Intensity and the 71-13
BASELINE CLIPPER controls until the pulsed spectrum,
about the 0 Hz response, can be observed (see Fig . 3-8) . It
may be necessary to adjust the output of the pulse
generator to approximately 0.1 V ; however, do not exceed
1 V peak .
d3m'
v
at'
0 - 'I+MHz 300KHZ1 f6 tc
f. Depress the PULSE STRETCHER pushbutton . Note
that the intensity of the pulsed spectra increases . Return
the pushbutton to its off position .
g . Switch AUTO PHASE LOCKED mode OFF, and
tune the 0 Hz response to the left edge of the screen .
Decrease the FREQ SPAN/DIV to 0 and switch the
TIME/DIV to the 10 us position . Switch the Trigger
SOURCE to INT and the Trigger MODE to NORM, then
adjust the Trigger LEVEL control for a triggered display of
two or more pulses .
0
-so
(A) Display without PULSE STRETCHING .
NOTE
To increase the display amplitude, tune the CENTER
FREQUENCY towards 10 MHz and increase the
pulse generator output until the signal amplitude
equals 4 divisons .
h . Depress the PULSE STRETCHER button and note
that the pulse falltime increases to approximately 10 us
(2 .5 us/DIV) .
i . Return the TIME/DIV selector to the 0.1 s position,
the FREQ SPAN/DIV to 10 MHz, and release the PULSE
STRETCHER pushbutton .
Disconnect the pulse
generator signal to the RF Input connector.
7. Check Triggering Operation and Sensitivity
a. Apply a 100 MHz signal from the VHF signal
generator to the RF Input of the 71-13 and tune the
CENTER FREQUENCY to the signal .
b. Apply a 10 kHz signal from the sine wave signal
generator; through a "T" connector, BNC to BNC cable,
and BNC to pin-jack cable, to both the EXT IN
HORIZ/TRIG jacks on the 71-13 and the External Modulation Input of the VHF signal generator (see Fig. 3-9) .
c . Modulate the VHF signal with a O.5 V peak-to-peak,
10 kHz signal .
NOTE
If the output of the sine wave generator is not
calibrated, monitor its output with a test oscilloscope .
(B) Same display with PULSE STRETCHING .
Fig. 3-8. Displays of a pulsed spectra that illustrate the effect of
the PULSE STRETCHER.
d . With the CENTER FREQUENCY of the 71-13 tuned
to the 100 MHz signal from the VHF signal generator,
uncouple the FREQ SPAN/DIV and reduce the span to 0,
leaving the RESOLUTION at 3 MHz . Switch the display
mode to LIN.
e. Adjust the VHF signal generator output for a display
amplitude of 1 divison . Switch the Triggering to INT
(SOURCE) and NORM (MODE) . Set the TIME/DIV to
.1 ms .
f. Adjust the TRIGGERING LEVEL for a triggered
display, then reduce the VHF signal generator output to
decrease the display amplitude to 0.5 division and ensure
that the 71-13 will still trigger on the 1 kHz modulation .
3-13
Performance Check-71-13
7000 Series Oscilloscope
with 71-13 Spectrum Analyzer
Fig. 3-9. Equipment setup to check triggering operation.
g. Check triggering operation through the frequency
range of 15 Hz to 1 MHz, maintaining 0.5 division of
display.
h. Switch the TRIGGERING (SOURCE) to EXT . Set
the sine wave generator output level for 0.5 V peak-topeak at 10 kHz.
i . Check triggering through the frequency range of
15 Hz to 1 MHz as described in step g . Ensure that the
input level remains at 0.5 V peak-to-peak .
j. Switch the TRIGGERING (SOURCE) to FREE RUN
and note that the display will not trigger.
k . Switch the TRIGGERING (SOURCE) to LINE and
check that the display triggers at line frequency.
I. Switch the TRIGGERING (MODE) to SGL SWP and
the TIME/DIV to 1 s. Check for a single sweep each time
the sweep button is pushed .
NOTE
The pushbutton should light during sweep time .
3- 1 4
m . Return the TRIGGERING (SOURCE) to FREE RUN
and the (MODE) to NORM .
8. Check the External Horizontal Input Voltage
Requirement . (0 V to 10 V ±1 V should sweep the
analyzer the full span .)
a. Switch the oscilloscope (mainframe) Vert Mode
switch off the vertical signal (right for 3-hole mainframes)
and the 71-13 TIME/DIV to EXT.
b. With no signal applied to the EXT IN HORIZ/TRIG
input jacks, position the crt beam to the left graticule edge
to establish 0 V, 0 Hz reference .
c. Apply a variable voltage source, such as a variable
power supply, to the EXT IN HORIZ/TRIG pin-jacks and
adjust the voltage source so the beam is deflected the full
span . Check that the voltage source equals +10 V ±1 V.
NOTE : The sine wave generator can be used to check
external sweep operation as follows :
1) After the beam has been positioned to the 0 V,
0 Hz reference, apply a 10 V peak (positive swing will
go to +10 V), 10 Hz sine wave to the EXT IN connectors .
Performance Check-71-13
2) The crt beam should sweep to the graticule
centerline when the input voltage is 10 V peak f1 V.
10 . Check Frequency Span Accuracy and Linearity.
(Freq Span accuracy within 5%, linearity accuracy
within 5% over the center 8 divisions.)
d . Disconnect the pin-jacks to the EXT IN connectors ;
return the TIME/DIV selector to 50 ms and the oscilloscope Vert Mode to Left .
a. Apply the marker and trigger output from the time
mark generator through the Harmonic Modulator to the
RF Input of the 71-13. Set the 71-13 selectors and controls
as follows:
9. Check the Video Output Level. (50 mV t5% per
displayed division about the crt center.)
FREQUENCY
Display Mode
RF Attenuator
REFERENCE LEVEL
PHASE LOCKED Mode
FREQ SPAN DIV
RESOLUTION
(Uncoupled)
a. Apply the VIDEO OUT signal to the Input of a
vertical amplifier unit in the test oscilloscope . Use the pinjack to BNC cable adapter. Set the Volts/Div selector of the
amplifier to 50 mV .
b. Apply the CAL OUT signal to the RF Input of the
71-13, set the FREQ SPAN/DIV to 2 MHz, and tune the
CENTER FREQUENCY to center one of the 50 MHz
markers in the display.
800 MHz
10 dB/DIV
O dB
-30 dBm
ON
100 MHz
3 MHz
b . Check frequency span accuracy and linearity as per
Table 3-2 .
c. Adjust the RF Attenuator and the Gain of the 71-13
for a signal amplitude of 4 divisons, then position the
display about the vertical center of the crt with the
VERTICAL POSITION control. Adjust the REF VARiable
control for precisely 4 divisons of signal amplitude.
NOTE
A t some settings a better display may be obtained by
using the VIDEO FILTER or by tuning the FREQUENCY to a different setting. When the VIDEO
FILTER is used, the sweep speed must be decreased
to obtain optimum marker amplitude.
d. Check the video output amplitude on the test
oscilloscope . Amplitude should equal 200 mV ±10 mV .
TABLE 3-2
FREQ SPAN/DIV
RESOLUTION
100 MHz
50 MHz
20 MHz
10 MHz
5 MHz
2 MHz
1 MHz
.5 MHz
.2 MHz
.1 MHz
50 kHz
20 kHz
10 kHz
5 kHz
2 kHz
1 kHz
.5 kHz
200 Hz
3 MHz
3 MHz
300 kHz
300 kHz
300 kHz
300 kHz
30 kHz
30 kHz
30 kHz
30 kHz
3 kHz
3 kHz
300 Hz
300 Hz
300 Hz
300 Hz
300 Hz
30 Hz
Marker
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
Time Mark Generator
Trigger
Markers/Div
0
0
0
.1 us
.1 ps
.1 Ps
1 us
1 PS
10 ps
lops
10 /is
10 ps
.1 ms
.1 ms
.1 ms
1 ms
1 ms
1 ms
1 per div
1 per 2 div
1 per 5 div
1 per div
1 per 2 div
1 per 5 div
1 per div
1 per 2 div
2 per div
1 per div
1 per 2 div
1 per 5 div
1 per div
1 per 2 div
1 per 5 div
1 per div
1 per 2 div
1 per 5 div
Tolerance
(over center
8 div)
5%
5%
5%
5%
5%
5%
5%
5%
5%
5%
5%
5%
5%
5%
5%
5%
5%
5%
3- 1 5
Performance Check-71-13
11 . Check the Time/Div Accuracy .
within 2% of the sweep rate selected .)
(Accuracy
a . Switch the RF Attenuator to 0 dB and the Gain
selector fully ccw for a REFERENCE LEVEL of -30 dB .
b. Apply a 100 MHz, -40 dBm signal from the VHF
signal generator to the RF INput of the 71-13 and tune the
CENTER FREQUENCY to the signal . Apply .1 ms time
markers from the Marker Output of the time mark
generator to the External Modulation input of the VHF
signal generator (see Fig . 3-10) so the signal generator
output can be modulated by time markers.
c . With the CENTER FREQUENCY tuned to the
100 MHz signal from the VHF signal generator, uncouple
the FREQ SPAN/DIV selector and reduce the span to 0,
leaving the RESOLUTION at 3 MHz. Switch the display
mode to 2 dB/DIV .
d. Switch the TRIGGERING to INT (SOURCE) and
NORM (MODE) and the TIME/DIV to .1 ms . Adjust the
VHF signal generator output for a display amplitude of
approximately 2 divisions (see Fig . 3-11) .
EE_
Edam
rs
0 ov*MH
_U_
I
i
MHz
a~ '°
i -50
low
Fig. 3-11 . Display showing time markers for checking TIME/DIV
accuracy .
e . Adjust the TRIGGERING LEVEL for a triggered
display, then check the accuracy of the TIME/DIV selections by applying appropriate markers from the time mark
generator and noting the displacement error between the
graticule marks and the time markers. The error must not
exceed ±2% (0 .2 div) over the center 8 divisions of a
10 division display .
7000 Series Oscilloscope
with 71-13 Spectrum Analyzer
ccacT-'~_-`
Marker Ou
Fig. 3-10 . Test equipment setup to check TIME/DIV accuracy.
Performance Check-71-13
NOTE
Use the HORIZ POSITION control to position a
marker on the 1st graticule line, then note the error
between each marker and its respective graticule
line .
f. Disconnect the signal to the RF INput and return the
71-13 to normal spectrum operation.
This completes the performance check for the 71-13. It
will now perform within the specifications described in
Section 1 .
Section 4-71-13
CALIBRATION PROCEDURE
This section provides procedural information for internal checks and adjustment . Performing the complete
procedure will recalibrate the instrument to its
specifications . After calibration, the instrument performance can be verified by performing the Performance
Check .
Limits, tolerances, and waveform illustrations in this
procedure are guides or aids to calibrate the instrument;
they are not intended as instrument specifications .
Waveform illustrations are typical.
Complete or Partial Calibration
The instrument should be cleaned and inspected as
outlined in the Maintenance section, before performing a
complete calibration . Perform the checks and adjustments in sequence for a complete calibration, then
verify the performance by the Performance Check .
Many circuits within this instrument, are very stable,
and some require extensive facilities with expensive test
equipment to calibrate. It may therefore be desirable, to
perform only a partial calibration . Turn to the desired step,
prepare the instrument for adjustment by referring to the
nearest setup and control instructions, proceeding the
step, then adjust or calibrate as directed .
History Information
The manual and instrument are constantly evaluated
and updated . These modifications may require changes in
the calibration procedure . History information that is
applicable to earlier instruments is included either as a
deviation within a step or as a subpart to a step.
Interaction
Differential Comparator (optional) : Common mode
signal range ±10 V, comparator accuracy 0 .1% . Tektronix
7A13 plug-in unit.
Adapter : BNC female to subminiature (SEALECTRO)
female . Tektronix Part No. 175-1162-00, SEALECTRO
Part No . 51-077-6801 .
Adapter: SEALECTRO male to male. Tektronix Part No .
103-0098-00, SEALECTRO Part No. 51-072-0000 .
Shorting Strap or Jumper: Jumper lead approximately
4 inches long with miniature alligator clips.
00.
Plug-in Extenders (three) : Tektronix Part No. 067-0616-
SHORT
Equipment for calibration includes the equipment
listed for the Performance Check plus the following
additional equipment:
DC voltmeter : Checked to within 1% at 15 V, 5 V and
20 V, for example; Triplett Model 630-PL.
AND
The following abridged procedure provides a calibration record and an index to help locate adjustment steps .
71_13 Serial No .
Calibration Date
Calibrator
TIME BASE SECTION
1.
Adjustments that interact with other circuits are noted
and reference is made to the affected circuit which may
require re-adjustment .
Equipment Required
FORM PROCEDURE
RECORD
Adjust Sweep Length,
Offset, and Triggering
Timing,
Page 4-3
FUNCTION IF
2.
Adjust LIN Mode Baseline Offset
Page 4-6
3.
Adjust Gain Compensation and
Calibrate the Reference Level
Page 4-6
1ST LO PHASE LOCK
4.
Error Amplifier Offset Adjustment
Page 4-8
.13
Calibration Procedure-71
Preliminary Procedure
FREQ SPAN AND 1ST LO CALIBRATION
5.
6.
Adjust the Frequency Span of the
1st LO and 16-19 MHz Oscillator
Calibrate the Center Frequency and
Frequency Readout
PHASE
7.
8.
LOCK CALIBRATION
JUSTMENTS
Page 4-8
Page 4-10
AD-
Adjust the Memory Gain
Adjust the Error Amplifier Gain
Page 4-11
Adjust the Bandpass of the 105 MHz
IF Amplifier and 300 kHz Filter
Page 4-12
10 . Adjust the Resolution Gain Leveling
Compensation
Page 4-14
11 . Adjust the Post Resolution Amplifier
Gain
Page 4-16
12 . Minimize Intermodulation Products
Page 4-16
1 . Check the front panel controls and selectors for
smooth operation and proper indexing .
2 . Remove the 71-13 from the mainframe and
reconnect it to the mainframe interface through the
flexible plug-in extenders. (Connect the 71-13 into the two
vertical and left horizontal compartments of four hole
mainframes .)
NOTE
50 MHz CALIBRATOR
13 . Adjust the Calibrator Output Level
Instrument calibration should be performed at a
temperature equal to the ambient operating
temperature that is normally within +20° C to +30° C
after a warmup period (with power on) of atleast 30
minutes to allow the instrument to stabilize.
Page 4-11
RESOLUTION
9.
NOTE
Page 4-16
The guide pin on the extender cable plug to the RF
section of the 71.13 must be removed before it will
plug into the interface connector. The guide pin is
removed by pulling it out with a pair of pliers.
3. Turn the power ON and allowthe instrument circuits
to stabilize before making any adjustments (approximately 20 minutes) .
Calibration Procedure-71-13
TIME BASE SECTION
1 . Adjust Sweep Length, Offset, and Triggering
Set the front panel controls and selectors as follows :
71-13
TIME/DIV
Triggering SOURCE
Triggering MODE
FREQ SPAN/DIV
RESOLUTION
Display Mode
.5 ms
FREE RUN
NORM
MAX
Coupled to the FREQ
SPAN
2 dB/DIV
Test Oscilloscope
Time/Div
Volts/div
(Calibrated)
Input Coupling
.1 ms
5V
do
f. Decrease the FREQ SPAN/DIV to .1 MHz, keeping
the marker centered with the CENTER FREQUENCY
control .
g . Increase the FREQ SPAN/DIV to 100 MHz and
adjust the Swp Offset with R1255 to bring the signal to the
center of the screen . This will eliminate signal shift as the
dispersion is changed .
h . Repeat steps f and g until the signal remains on
screen as the frequency span is decreased from
100 MHz/Div to approximately 200 kHz.
NOTE
The hysteresis in the tune control system may shift
the center frequency slightly when the frequency
span is switched back through its positions .
TRACK GEN
b . Connect the test oscilloscope probe to pin 3 of the
TRACK GEN connector (Fig . 4-1A) .
r-~
c. Adjust the Swp Gain with R1250 (Fig . 4-2) on the
sweep board, fora 20 volt (±10 V) sweep ramp (Fig . 4-1 B) .
Adjust R1255 (Fig . 4-2) to center the ramp about 0 volts.
NOTE
This sweep ramp should be an accurate 20 volt
(±10 V) ramp . If a differential comparator plug-in
(A)
unit (e .g ., 7A13) is available, use the comparator to
measure the amplitude and offset of the sweep
ramp .
The offset level should be adjusted to 0 volt with
R1255 (Swp Offset) .
d . Adjust the sweep length of the 71-13 to 10 divisions,
with the front panel SWP CAL, then center the trace within
the graticule area . Apply the CAL OUT signal to the RF
INput and switch the display mode to 10 dB/DIV .
e . Change the FREG SPAN/DIV to 10 MHz and tune
the center frequency to one of the calibrator markers.
(B)
Location of pin 3 on the TRACK GEN connector .
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Adjust R1250 for an accurate 20-volt ramp .
Fig . 4-1 . Calibrating the sweep ramp .
Calibration Procedure-7t_13
Fig. 4-2. Location of adjustments on the Sweep board.
i . Switch the display mode to 2 dB/DIV . Turn the
BASELINE CLIPPER fully ccw. Pull transistor Q1210
(Fig 4-3) and use a screwdriver with a small blade to short
between the base and collector terminals. This pulls the
collector terminal to ground potential and disables the
sweep so a reference near center screen is provided .
j . Position the crt beam at the center line of the
graticule with Integrator Offset Adjust R1215 (Fig . 4-2) .
Replace transistor 01210.
k. Remove the flexible extender plug from the right
vertical compartment of the 71-13 mainframe oscilloscope
and install a vertical amplifier unit (e .g ., 7A16, 7A18) .
I. Switch the mainframe trigger Source to Vert Mode
and apply the 40 mV Calibrator signal to the amplifier
input. Set the Volts/Div to .1 V .
m . Switch the 71-13 TRIGGERING SOURCE to INT
and adjust the LEVEL control for a triggered display.
4-4
Use . ; screwdriver
short between the
base and collector
terminals
Fig. 4-3. Base to collector terminals for 01210.
n . Check that the display triggers on either the+ orslope. If the index mark on the LEVEL control is off center,
loosen the set screws and reposition the control.
Calibration Procedure-71-13
r~
o. Change the TRIGGERING MODE to SGL SWP and
the TIME/DIV to .5 s.
s. Adjust the Time/Div Cal R1190 (Fig . 4-2) for 1
marker/division .
p. Check that the sweep runs each time the sweep
button is pushed and that the button lights while the sweep
is running.
t. Check the timing accuracy for each TIME/DIV
selection. Timing accuracy must be within 5% .
NOTE
The remaining triggering modes of operation can be
checked if desired by referring to the Performance
Check section of the manual.
q. Return the TRIGGERING MODE to NORM, the
TIME/DIV to 1 ms and remove the signal from the
Calibrator to the vertical amplifier plug-in unit . Apply 1 ms
markers from a time mark generator (e.g ., 2901) through a
50 0 feedthrough termination, to the Input of the vertical
amplifier unit . Set the VoltslDiv to .5 V.
r. Adjust the 71-13 TRIGGERING LEVEL control for a
triggered display.
u . Change the TIME/DIV to 50 /is and apply 50 ps
markers from the time mark generator.
v. Adjust Miller
marker/division.
Offset
R1200
(Fig . 4-2)
for
1
w . Repeat 1 ms/DIV and 50 ps/DIV adjustments to
compensate for interaction .
x. Disconnect the signal from the time mark generator,
remove the vertical plug-in unit and reconnect the extender from the 71-13 interface to the right vertical
interface connector.
CParloic
FUNCTION IF ALIGNMENT
Preliminary
Pull the harmonica (multipin) connector P560, on the
Function IF circuit board (Fig . 4-4) .
Set the following controls to the positions indicated .
71-13
RF Attenuator
Gain Selector
REF VAR
Display Mode
TIME/DIV
Triggering
MODE
SOURCE
FREQ SPAN/DIV
RESOLUTION
0 dB
Fully ccw
CAL
LIN
20 ms
NORM
FREE RUN
50 MHz
3 MHz
Oscilloscope
Vertical Mode
Horizontal Mode
Right
A (if applicable)
2. Adjust the Lin Mode Baseline Offset
a . Position the trace to the lower area of the graticule
with the VERTICAL POSition control .
b. Adjust the Lin Baseline Offset R803 (Fig . 4-4)
clockwise, from a fully ccw position to a point where the
trace stops moving down . (Do not adjust past this point) .
c . Switch between LIN and LOG display modes,
checking the baseline shift. Repeat the Offset adjustment
if the baseline shifts .
3. Adjust the Gain Compensation and Calibrate the
Reference Level
a. Switch the display mode to 2 dB/DIV and position
the baseline of the display on the bottom graticule line if
necessary .
b . Apply a 10 MHz signal at -10 dBm, from a
calibrated signal source, through appropriate adapters
(BNC female to SEALECTRO female, SEALECTRO male
to male adapter, and SEALECTRO female to harmonica
connector) to P560 . (Fig . 4-4) . Part numbers for these
adapters are provided under Equipment Required List . If
an accurate 10 dB, 50 Q step attenuator is available,
connect it in series with the signal source .
Fig . 4-4 . Calibration adjustments and test points on the Function IF board .
4-6
Calibration Procedure-71.13
c. Adjust the 2 dBm/Div Ref Level R801 (Fig . 4-4) so
the trace is at the 5th graticule line down from the top.
d . Increase the signal input level 10 dB . Adjust the
front panel LOG CAL for a 5 division increase in signal
amplitude, (trace is at the top graticule line) .
e. Return the signal level to -10 dBm. Repeat steps c
and d to null the interaction between the adjustments.
NOTE
Because of some mainframe drift, it is advisable to
periodically remove the signal and check that the
display baseline returns to the bottom graticule line.
'~
k. Increase the signal level to 0 dBm, then adjust the
10 dB Ref Linearity R542 (Fig . 4-4) so the trace is at the
graticule line .
I. Decrease signal level in 10 dB steps, checking the
display calibration for the 10 dB/DIV mode . Trace should
shift down 1 f0 .1 division per each 10 dB step, to a
maximum of 1 .5 dB overthe 70 dB dynamic range. Repeat
steps h through k until this accuracy is obtained .
m . Set the signal input level to-20 dB m and switch the
display mode to2 dB/DIV . If necessary, adjust the trace to
the bottom graticule line with the VERTICAL POSITION
control .
n. Increase the Gain selector setting 50 dB so the
REFERENCE LEVEL readout is -80 dBm .
f. Switch the display mode to LIN and the signal input
level to 0 dBm.
o. Adjust the 40 dB Gain R603 (Fig . 4-4) so the trace is
at the reference level or top of the graticule .
g . Adjust Lin Ref Level R733 (Fig . 4-4) so the trace is at
the top graticule line .
p. Decrease the signal level to -40 dBm. If necessary,
position the trace on the bottom graticule line with the
VERTICAL POSITION control.
h . Switch the display mode to 10 dB/DIV . Decrease
the signal input level to -70 dBm .
i . Adjust the 10 dB/DIV Ref Level R802, (Fig . 4-4) so
the trace is 7 divisions down from the top graticule line .
j . Increase the signal input level so it is -10 dBm.
Adjust the trace so it is 1 division from the top graticule line
with 10 dB/DIV R703 (Fig . 4-4) .
q . Increase the Gain selector setting 20 db for a
REFERENCE LEVEL readout of -100 dBm .
r. Adjust the 60 dB Gain R663, (Fig . 4-4) so the trace is
at the reference level .
s . Remove the signal from the input to the Function IF
amplifier and replace the connector P560 .
Calibration Procedure-71.13
Fig . 4-5 . Grounding strap connected to pin 2 of U2200 .
Fig . 4-6 . Location of P69 and R51 on Hybrid Assembly A50.
1st LO PHASE LOCK LOOP
a. Set the front panel selectors as follows:
4 . Error Amplifier Offset Adjustment
a . Switch the 71_13 into phase locked mode by setting
the FREQ SPAN/DIV to 50 kHz and switch the AUTO
PHASE LOCKED switch on . Ground pin 2 of U2200 on the
tune control circuit board, with a jumper strap (Fig . 4-5) .
Remove P69 (Fig . 4-6) from the hybrid assembly A50 .
b . Set the test oscilloscope Time/Div to 10 ms and the
vertical amplifier deflection sensitivity to 1 V/div . Connect
the test oscilloscope probe to J69 and observe the beat
signal from the error amplifier .
c . Adjust R51, (Fig . 4-6) so the do reference level of the
error signal is 0 volt .
d . Check for a beat note amplitude that equals or
exceeds 4 volts peak-to-peak through the frequency
range of the 71-13 .
e . Reconnect P69 and remove the grounding strap to
pin 2 of U2200 .
FREQUENCY SPAN AND
CALIBRATION
1st
LO
5. Adjust the Frequency Span of the 1st LO and 1619 MHz Oscillators
NOTE
If the gain and offset adjustments run out of range
during this procedure, check the accuracy of the
20 volt ramp as set in step 1 .
4-8
FREQ SPAN/DIV
100 MHz
RESOLUTION (Uncoupled) 3 MHz
TIME/DIV
CENTER FREQUENCY
Display Mode
REFERENCE LEVEL
VIDEO FILTER
SWP CAL
10 ms
500 MHz
10 dB/DIV
Minimum sensitivity, then
increase for full screen
display .
30 kHz
10 division trace
b . Apply the marker and Trigger output of the time
mark generator through the Harmonic Modulator (0670640-00) to the RF INput of the 71-13 . Switch on the 10 ns
markers . This provides 100 MHz markers . If this equipment is not available the 50 MHz Calibrator signal can be
used .
c . Adjust the YIG oscillator driver gain with R2510
(Fig . 4-7) to calibrate the 100 MHz/div frequency span at 1
marker/division (see Fig . 4-8) .
NOTE
Adjusting the driver gain also adjusts the display
offset. The gain should be adjusted for the correct
marker interval and the offset should be adjusted
last. It may be helpful to hold one marker at screen
center while adjusting the gain so the markers fall on
graticule lines each side of center .
d . Switch the FREQ SPAN/DIV to MAX and increase
the RF Attenuator setting to 60 dB to attenuate the time
markers . Adjust the offset to the YIG oscillator main coil
with R2505 (Fig . 4-7) so the 0 Hz marker is at the left edge
or start of the display .
Calibration Procedure-7L13
Fig. 4-7. Location of the YIG Driver and Voltage Memory adjustments .
e . Decrease the RF Attenuator setting to 0 dB, FREQ
SPAN/DIV to 1 MHz, and the RESOLUTION bandwidth to
30 kHz. Apply 10 ns markers and 1 us trigger signals from
the time mark generator.
g . Decrease the FREQ SPAN/DIV to 50 kHz,
RESOLUTION bandwidth to 3 kHz, and the TIME/DIV to
20 ms . Apply 10,us trigger signals and 10 ns markers to
the Input .
f. Adjust the FM coil driver gain with R2530, (Fig . 4-7)
to calibrate the 1 MHz/div frequency span .
h . Adjust the 16-19 MHz sweep gain with R1960,
(Fig . 4-9) for 1 marker/2 divisons .
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Fig. 4-8. 100 MHz markers on a 100 MHz/DIV frequency span .
Fig. 4-9. Location of R1069, Sweep Driver adjustment for the 1619 MHz oscillator.
4- 9
Calibration Procedure-71-13
i . Return the FREQ SPAN/DIV to MAX, RESOLUTION
to 3 MHz, and the TIME/DIV to 10 ms .
j . Check the frequency span accuracy as per the
procedure in the Performance Check Section .
6. Calibrate the Center Frequency and Frequency
Readout
Couple the FREQ SPAN/DIV and RESOLUTION selectors together and switch the FREQ SPAN/DIV to 100 MHz.
Tune the CENTER FREQUENCY for an LED readout of
0888 .
b. Adjust the DVM reference current with R2065
(Fig . 4-10) so the mainframe readout matches the 71-13
readout. (This adjustment is not necessary if the 71-13 is
operated in a non-readout mainframe.)
c. Apply 10 ns markers from the time mark generator.
Couple the FREQ SPAN/DIV to the RESOLUTION selector and switch the FREQ SPAN/DIV to 100 MHz. Tune the
CENTER FREQUENCY to center the 900 MHz marker on
screen as the FREQ SPAN/DIV is decreased to 1 MHz.
(The 900 MHz marker is the 9th marker to the right of the
0 Hz marker .)
d . Adjust the DVM offset with R2135 (Fig . 4-10) so the
LED readout is 900 MHz.
e . Return the FREQ SPAN/DIV to 100 MHz and tune
the CENTER FREQUENCY to the 100 MHz marker .
Reduce the FREQ SPAN/DIV to 1 MHz, so the 100 MHz
signal can be accurately tuned to center screen .
f. Adjust the DVM gain with R2110, (Fig . 4-10) so the
LED readout is 0100 .
g . Repeat the offset and gain adjustments respectively, to compensate for any interaction .
Fig . 4-10 . Frequency Readout circuit adjustments .
h . Check the readout tracking accuracy from 0100 to
1800 MHz in 100 MHz increments, approach each check
point from the low side . Accuracy must equal
±(5 MHz + 10% of the Freq Span/Div) .
i. Switch the FREQ SPAN/DIV to MAX.
j. Check that the center frequency marker position
corresponds to the CENTER FREQUENCY through the
tuning range .
PLACHODJS
Calibration Procedure-7L13
7 . Adjust the Memory Gain
a . Couple the FREQ SPAN/DIV and RESOLUTION
selectors together, then switch the FREQ SPAN/DIV and
RESOLUTION to 10 MHz/300 kHz . Turn the error
amplifier loop gain R1755 (Fig . 4-11 B) fully cw . Connect a
shorting strap across S2608 (Fig . 4-11 A) . Apply the CAL
OUT signal to RF INput and tune the CENTER FREQUENCY to one of the calibrator markers .
b . Switch the front panel AUTO PHASE LOCKED
switch off, decrease the FREQ SPAN/DIV and
RESOLUTION to 50 kHz/30 kHz, keeping the signal
within the display area with the CENTER FREQUENCY
tuning .
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c. Tune the CENTER FREQUENCY so the signal is
approximately two divisions to the right of center .
d . Switch the AUTO PHASE LOCKED switch on and
off while adjusting R2605 (Fig . 4-12) so the signal locks
near the same position it was at with phase lock off . If it
appears that R2605 does not have enough range, proceed
with step e .
81755
e. Switch the phase lock off and tune the signal two
divisions to the left of center .
(B)
f. Switch the phase lock on and off and check that the
signal locks remain near the same point.
Phase lock error amplifier gain and adjustment .
Fig . 4-11 . Location of the Phase Lock calibration adjustments.
g . Remove the shorting strap across S2608. Switch the
AUTO PHASE LOCKED switch on and center the signal
on screen .
8. Adjust the Error Amplifier Gain
a . With the signal centered, decrease the FREQ
SPAN/DIV and RESOLUTION to 200 Hz/30 Hz . Switch
the display mode to 10 dB/DIV and decrease the sweep
rate so the display remains calibrated . Switch the mainframe to Store mode so the full span can be observed .
b. Adjust 81755 (Fig . 4-11 B) to obtain the best signal
to noise ratio and still maintain phase lock . If phase lock is
lost, turn 81755 cw and repeat the above procedure.
'-
c. Switch FREQ SPANQDIV to 5 kHz, RESOLUTION
to 3 kHz. Check that the noise level, 25 kHz from center, is
down at least 70 dB from the signal reference level .
Fig . 4-12 . Location of Memory Adjust 82605 .
4- 1 1
CParloic
RESOLUTION
9. Adjust the Bandpass of the 105 MHz IF Amplifier
and 300 kHz Filter
a. Set the following front panel selectors to the
positions indicated .
FREQUENCY
FREQ SPAN/DIV
RESOLUTION
400 MHz
1 MHz
30 kHz (Uncoupled from
the FREQ SPAN/DIV
selector)
2 dB/DIV
On
10 ms
OFF
Display Mode
Phase Lock
TIME/DIV
VIDEO FILTER
Helical resonator : Adjust 1st two
on left for bandpass shape and the
right adjustment for center freq .
b. Apply either a 400 MHz signal from a signal
generator, or the 50 MHz CAL OUT signal from the 71_13
calibrator to the RF INput. Adjust the generator output or
the gain from the 71-13, until the 400 MHz signal is
displayed on screen . Center the signal on screen with the
tuning control.
c. Change the RESOLUTION to 3 MHz and establish a
signal amplitude of approximately 7 divisions with the
signal generator output control or the 71-13 REF VARiable
control.
d. Adjust the response of the 105 MHz IF amplifier, and
the wide filter bandpass, with C82, the 3 MHz helical
resonator. (Fig . 4-13) and C456, in the filter circuit. (Fig .
4-14) so the response is similar to that illustrated in Fig .
4-16 .
(B)
Center section extended so 105 MHz, 3 MHz bandwidth
helical resonators can be adjusted .
Fig . 4-13 . 105 MHz IF and 3 MHz bandwidth adjustments .
NOTE
Keep the signal centered as the tuning adjustments
are made . Switch back to 30 kHz or 3 kHz
RESOLUTION periodically, to ensure that the signal
is tuned to the graticule center. This locates the
center of the 10 MHz IF. There is no recommended
sequence of adjustments, however, the following is
applicable for most instruments:
1) Adjust C82 so the response moves slightly to the
left of center or the low frequency side of the display.
2) Adjust the input and center resonators to shape
the display and the output resonator to keep the
response centered .
3) Adjust C456 (Fig . 4-14) for maximum bandwidth
and amplitude.
Fig . 4-14 . Wide-Band Filter adjust C456 .
Calibration Procedure-7L13
Bandpass, at the -6 dB down point, should equal
3 MHz ±10% ; however, the bandwidth specification is
within 20% of the resolution bandwidth selected . The
response flatness can vary as much as 2 dB . Fig . 4-15
illustrates this variation with dashed lines . The shape
should resemble that of the illustration .
t,
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Jumper P304 r
for relay K357e
(remove)
able W356 on P303
(Remove and plug
J307 on,;.-, ()" '
Flatness can
vary as much
as 2 dB
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Fig. 4-15 . Typical response characteristics for the 105 MHz IF
through the Wide Filter.
e. Set the FREQ SPAN/DIV to .1 MHz and the
RESOLUTION to 30 kHz. Carefully center the signal with
the tuning controls .
NOTE
It is important to calibrate in the phase lock mode.
Remove the shield cover over the post-resolution
amplifier. Remove P304 (jumper for relay K357, see Fig.
4-16A) . Remove P301 and P303, of cables W307 and W356 .
Connect P301 of cable W307 to J303 . Ensure that the
signal lead, of P303, is connected to pin 1 of J303 .
f. Change the RESOLUTION to 3 MHz. Adjust the
narrow filter circuits with C472 and C475 (Fig . 4-16A), for
a flat-topped response that is similar to that illustrated in
Fig . 4-16B. Keep the response centered as these adjustments are made . Do not change the front panel tuning
control setting or the frequency of the signal generator .
Bandpass at the 6 dB down point, should range between
500 kHz to 600 kHz.
5 0 kHz to 600 kHz
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(B)
Typical flat top response when narrow filter is adjusted
correctly .
Fig. 4-16. Connections, adjustments, and typical response when
adjusting the Narrow Post-Amplifier Filter.
g . Reconnect, the plugs for cables W307 and W356, to
their respective pins and replace the jumper plug for relay
K357 .
h. Switch the RESOLUTION to 30 kHz, FREQ
SPAN/DIV to 100 kHz. Ensure that the signal is still
centered on screen . If necessary, tune the signal to center
then switch the RESOLUTION to 300 kHz.
Calibration Procedure-7L13
i. Adjust the 300 kHz filter, with C322 through C348
(Fig . 4-17A), for a response that is similar to that shown in
Fig . 4-1713 .
NOTE
If the response is similar to the illustration of Fig.
4-17, try tweaking each capacitor a slight amount .
If the response is not centered or is assymetrical,
adjust the capacitors to center and peak the
amplitude of the response, then adjust each filteruntil the response is symmetrical and300 kHz±10%
wide . (The input and output resonators usually
affect the centering and bandwidth of the display
and the center resonators the display slope.)
_---_-_s_-
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9
E
d . Compensate the gain for each RESOLUTION setting, with the amplitude adjustments listed in Table 4-1
and illustrated in Fig. 4-18, so the signal amplitude
remains constant through all resolution settings .
,
NOTE
Decrease the sweep speed to maximize the signal
amplitude for the 300 Hz RESOLUTION setting .
r
TABLE 4-1
f
F
3
9
1
(A)
300 kHz filter shaper adjustments C322, C326, C328,
C342, C345, C348 .
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11
+
11,1
-6 dB down
300 kHz + 30 kHz
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i
(B)
300 kHz filter response .
Fig . 4-17 . 300 kHz Filter adjustments and typical response
characteristics .
4- 1 4
Leveling
a. With the signal phase locked, reduce the FREQ
SPAN/DIV to 10 kHz and switch the RESOLUTION to
30 kHz . Center the signal on screen with the tuning
control and set the signal amplitude to approximately 7
divisions with the REF VARiable control .
.
i
s
Gain
c . Switch the RESOLUTION between 30 kHz at
10 kHz/Div span and 3 kHz at 1 kHz/Div span . Select the
RESOLUTION setting with the lowest signal amplitude
and adjust the signal level to 7 divisions with the REF
VARiable control .
I
i
i .
Resolution
b . Preset R367 and R377 for maximum amplitude at
3 kHz and 30 kHz resolution .
I
t
t
10 . Adjust the
Compensation .
RESOLUTION
3 MHz
.3 MHz
30 kHz
3 kHz
300 Hz
30 Hz
FREQUENCY
SPAN/DIV
ADJUST
1 MHz
.1 MHz
10 kHz
1 kHz
.5 kHz
200 Hz
R307 (3 MHz Ampl)
R2705 (300 kHz Ampl)
R367 (30 kHz Ampl)
R377 (3 kHz Ampl)
R387 (300 Hz Ampl)
82730 (30 Hz Ampl)
e . Change the FREQ SPAN/DIV to 1 MHz,
RESOLUTION to 3 MHz, RF Attenuator to 0 dB, and turn
the Gain selector fully ccw. Position the baseline of the
display on the bottom graticule line, then adjust the REF
VARiable control for a signal level of 7 divisions. If you run
out of range on the REF VARiable control, tune to a lower
frequency signal .
f. Switch the RF Attenuator to 10 dB and increase the
Gain setting 10 dB (one position cw from the reference
setting) .
g . Adjust the 10 dB gain R267 (Fig . 4-18) so the signal
amplitude equals the 7 division reference amplitude established in step e .
h . Increase the RF Attenuator setting to 20 dB and the
Gain setting an additional 10 dB . Switch in the 300 Hz
VIDEO FILTER .
i . Adjust the 20 dB Gain R297, (Fig . 4-18) sothesignal
amplitude is again 7 divisions.
Calibration Procedure-7L13
Pr-11111,m
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dB GAIN
82730
>J Hz
AMPL
(B)
Gain compensation adjustments on the YIG driver, 30 Hz filter circuit boar
Fig . 4-18 . Resolution gain compensating adjustments.
4- 1 5
Calibration Procedure-71
.13
j. Switch the RF Attenuator to 30 dB and increase the
Gain setting 10 dB. Check that the signal amplitude
equals 7 divisions f0 .5 divisions . Since there is no
adjustment for 30 dB gain, it may be necessary to
compromise between the 10 dB gain adjustment and the
20 dB gain adjustment .
k. Apply the CAL OUT signal through a 10 d8 step
attenuator (such as Hewlett Packard Model 355D) to the
RF INput ; orapply a 50 MHz signal from a signal generator
with a calibrated variable attenuator, such as Hewlett
Packard Model 608D, to the 71-13 RF INput .
I . Tune the signal to center screen . Decrease the FREQ
SPAN/DIV and RESOLUTION bandwidth to 200 Hz/30 Hz
while keeping the signal centered on screen with the
tuning control .
m. Switch the 300 Hz VIDEO FILTER on and the
display mode to 2 dB/DIV . Increase the signal input
attenuation, with the step attenuator or the variable
attenuation, while increasing the 71-13 gain until the
REFERENCE LEVEL is-100 dBm and the signal attenuation is 80 dB. The signal level is now -110 dBm .
n. Adjust the signal amplitude to some reference point
on the graticule, with the REF VARiable control . Increase
the signal attenuation 10 dB and switch the 10 dB GAIN
button on.
o. Adjust the signal amplitude to the reference established in step n, with R2735 (Fig. 4-18) .
p. Disconnect and remove the test equipment cables.
Switch the 10 dB GAIN off and return the REFERENCE
LEVEL to -30 dBm . Switch out the VIDEO FILTER .
11 . Adjust the Post Resolution Amplifier Gain
This adjustment sets the gain of the post resolution
amplifier so an input of -17 dBm will provide full screen
deflection .
a . Switch the FREQ SPAN/DIV to .1 MHz (100 kHz)
and the RESOLUTION to .3 MHz (300 kHz) . Set the
TIME/DIV to 10 ms . Switch the REF VARiable to CAL.
Switch the display mode to 2 dB/DIV and position the
trace at the bottom graticule line .
b. Apply a 10 MHz signal at -17 dBm, from the signal
generator, through a BNCto subminiature (SEALECTRO)
adapter, to J2700 (Fig . 4-18b) .
4-1 6
c. Adjust the post resolution amplifier gain with R425
(Fig. 4-18a) for a display reference level of 8 divisions .
d . Remove the cable from the signal generator to
J2700 and replace P2700 .
12. Minimize Intermodulation Products
a. Set the following front panel controls as indicated :
FREQ SPAN/DIV
RESOLUTION
Display Mode
RF Attenuator
Gain
REFERENCE LEVEL
.5 MHz
30 kHz
10 dB/DIV
0d13
Fully ccw
-30 dBm
b. Apply two signals, separated by 1 MHz, from two
50 Q signal generators, through 10X attenuators (for
isolation) then through a BNC "T" connector to the RF
INput . (Fig . 4-19) .
c. Tune the 71-13 CENTER FREQUENCY midway
between the two signals and adjust the output of the
generators so the amplitude of both signals is at least full
screen, or until sidebands can be observed on the display .
d . Adjust IM Adj C95 (Fig. 4-20) to minimize the
amplitude of the sidebands .
e. Remove the signal generator hookup to the RF
INput .
50 MHz CALIBRATOR
13. Adjust
t0 .3 dB)
the
Calibrator
Output
(-30 dBrn
Since the output of the 71-13 Calibrator contains
harmonics, direct power measurement is not possible.
The following are suggested methods and procedures :
Vector Voltmeter Method (Hewlett Packard Model 8405A
Vector Voltmeter)
1) Terminate the "A" probe, with a BNC 50 A
feedthrough termination and connect the probe through
the termination, to the CAL OUT connector on the 71-13.
Calibration Procedure-71-13
7000 Series Oscilloscope
with 71-13 Spectrum Analyzer
10X attenuators
for isolation and
BNC "T" connector
Fig. 4-19 . Equipment setup to measure IM distortion.
2) Switch the Vector Voltmeter frequency to 50 MHz.
3) Check that the RMS reading is between 6.85 mV
and 7.3 mV (-30 dBm is 7.07 mV RMS, into 50 i2) .
4) The calibrator output level can be adjusted by,
removing the left vertical plug-in unit and the oscilloscope
left side panel to gain access to the 71-13 calibrator . Adjust
R956 (Fig . 4-21) for an output level of -30 dBm (7 .07 mV
RMS) .
C95
Adjust for minimum
3rd order intermodulation products
Fig. 4-20. Location of C95 in 3rd Mixer Assembly .
Fig. 4-21 . Location of R956, Calibrator Output Level adjustment .
4- 1 7
Calibration Procedure-71.13
Using a Power Meter (within 0.1 dB) and 50 MHz Low Pass
Filter, with 40 dB or more rolloff at 100 MHz through
2.0 GHz; (General Microwave Power Meter Model 454A, or
Hewlett Packard Model 432A Power Meter)
NOTE
The insertion loss of the filter and cables, must be
accounted for to an accuracy of 0.1 dB .
1) Connect the power meter through the filter to the
CAL OUT connector and measure the output level .
1) Set the FREQ SPAN/DIV to .5 MHz and the
RESOLUTION to .3 MHz . Switch the RF attenuator to
10 dB and the Gain selector fully ccw. Push in the
2 dB/DIV, LOG display button .
2) Apply a calibrated -30 dBm 50 MHz signal to the
RF INput of the 71-13 and tune the frequency to center the
signal in the graticule window . Adjust the VARIABLE Gain
control to position the top of the signal to a reference line
(2nd or 3rd from the top) .
2) If necessary, adjust the 71-13 calibrator output as
described in the Vector Voltmeter method (step 4) .
3) Disconnect the -30 dBm reference signal, then
apply the71
.13 CAL OUT signal to the RF I Nput connector.
Accurate -30 dBm Signal Source (Signal substitution
method)
4) Adjust R956 so the output of the 71-13 Calibrator is
-30 dBm .
NOTE
The power meters that were recommended for the
preceding method, can be used to verify the signal
source output level.
This completes the calibration of the 71.13. The Performance Check will verify that the instrument meets
specifications .
Section 5-71.13
CIRCUIT DESCRIPTION
This section describes the functions of the major
circuits in the 71-13 and their relationship in the overall
operation of the instrument . The description is general
and intended as an aid for the technician and operator to
help service or operate the instrument at maximum
efficiency . A general description of circuit concepts,
common to spectrum analyzers, is provided in Tektronix
Concept Booklet, "Spectrum Analyzer Circuit," Part No .
062-1055-00.
The section begins with a functional block diagram
description, followed with more detailed analysis of the
major circuits . Positive logic is used for digital circuits .
The diagrams contain typical waveform and voltage data
that should be helpful to understand circuit functions and
aid in troubleshooting the instrument .
BLOCK DIAGRAM
The 71-13 is a swept front end spectrum analyzer that
covers the frequency range from 1 kHz to 1 .8 GHz and
provides a frequency span of 1 .8 GHz. A detailed block
diagram in the Diagrams section, illustrates signal paths
and function of the major circuits . Refer to this diagram
while reading the description .
The input signal path to the 1 st mixer consists of a 0 to
60 dB step attenuator, a 1 .8 GHz low-pass filter, and a
3 dB isolation pad . The stop band for the filter begins at
2.095 GHz. The filter attenuates frequencies of 2 .095 GHz
(1st IF) and higher, that may exist between the 1st mixer
and the RF INput. This reduces susceptibility to image
responses, IF direct feed-through from the RF INput, and
keeps the 1st LO output from reaching the RF INput
connector.
The 1st mixer is a double-balanced type mixer, with its
input and output isolated by a 3 dB pad and a traveling
wave directional filter, respectively . The 3 dB pad reduces
VSWR interaction and improves the response flatness .
The traveling wave directional filter reduces intermodulation distortion and provides a termination for image
responses from the 1st mixer.
The frequency of the 1st LO is swept, when the
frequency span is 100 kHz/Div or more, through some
portion or all of the frequency range from 2.095 GHz to
3.895 GHz. The center frequency of the oscillator can also
be tuned through the selected frequency span . When the
frequency span is 50 kHz/Div or less, the 1st LO frequency
is fixed and the 2nd LO is swept through the selected span .
The output of the 1st mixer (1st IF) is centered at
2 .095 GHz. A bandpass filter 10 MHz wide (with a center
frequency of 1 .095 GHz) attenuates the upper sideband,
and a 2.2 GHz low-pass filter ensures the outband integrity of the bandpass filter . The 1st IF is converted to
105 MHz (2nd IF) in the 2nd mixer by mixing the 2nd LO
frequency of 2 .2 GHz with the 1st IF of 2.095 GHz.
The 2nd IF signal is amplified by a Pre-Resolution
amplifier, then reduced in bandwidth to 3 MHz by a threecavity helical resonator filter . The 105 MHz IF is converted
down to 10 MHz in the 3rd mixer by the 3rd LO frequency
off 95 MHz mixing with the 2nd IF of 105 MHz. Amplification and bandwidth of the 10 MHz 3rd IF, are controlled in
the resolution and function IF amplifier stages . Amplification is controlled by switching in amplifier stages .
Bandwidth is controlled, in decade steps from .3 MHz to
30 Hz, by switching bandpass filters into the signal path .
IF gain can be selected in 10 dB steps from 0 to 70 dB .
Gain stages are in the Pre-Resolution amplifier and the
Function IF amplifier, with an additional 10 dB of gain in
the 30 Hz filter . The additional 10 dB of gain may be added
only when the resolution bandwidth is 30 Hz and the
display mode is 2 dB/DIV or LIN . Variable gain between
the 10 dB steps, is provided by a variable gain stage in the
Post-Resolution amplifier.
The Function IF amplifier contains circuits for
logarithmic, linear, and vertical deflection factor . The log
displays are 2 dB/Div and 10 dB/Div . The amplifier also
compensates for the gain variation when the resolution
bandwidth and display modes are changed, so the
reference level remains constant through all combinations
of resolution and display modes .
The detected signal from the Function IF amplifier is
amplified and summed with voltage levels for vertical
positioning, then applied through push-pull amplifiers to
the oscilloscope mainframe interface. Three auxiliary
circuits can be switched into the video signal path . These
circuits provide; video filtering (30 kHz, 300 Hz, and
10 Hz), pulsed video signal processing or pulse
stretching, and baseline suppression.
The sweep circuits provide the frequency base or time
base for the display. In the frequency domain, the output
from the sweep generator is applied through the horizontal amplifier to the mainframe interface, for the horizontal
deflection, and through the frequency span attenuator to
the 1 st or 2nd local oscillator, for frequency sweeping . The
frequency span of the display is therefore a function of
how much the 1st LO or the 2nd LO is swept .
Circuit Description-7L13
The sweep ramp from the sweep generator, is
attenuated in calibrated increments by the FREQ
SPAN/DIV attenuator, then applied through switch contacts to either the 1st LO (YIG) driver circuits or the voltage
controlled 16-19 MHz oscillator in the 2nd LO phase lock
loop .
A current ramp through the main tuning coil, sweeps
thelstLOforfrequency spans from 100 MHz/Divthrough
5 MHz/Div, the current ramp is then applied to the FM coil
of the YIG oscillator for spans of 2 MHz/Div through
0.1 MHz/Div. When the frequency span is decreased to
50 kHz/Div or less, the 1st LO may be phase locked and
the sweep ramp is applied through switch contacts to a
voltage controlled 16-19 MHz oscillator in the 2nd LO
phase lock loop . The 2nd LO phase lock loop is a servo
system which transmits changes of the 16-19 MHz oscillator frequency to the 2nd LO .
The marker (or ditch) that is displayed when the FREQ
SPAN/DIV selector is in MAX position, is produced by the
marker generator. The marker position is relative to the
setting of the TUNE control so it indicates to the operator
the portion of the span that will be display center, when the
frequency span is reduced. The marker, is summed with
the video at the amplifier that drives the vertical output
stage.
This completes the signal path flow and the function of
the frequency span circuits .
DETAILED CIRCUIT DESCRIPTION
The following is more detailed than the block diagram
description and should assist in servicing and operating
the instrument .
RF or Microwave Circuits O2
The RF section consists of sealed microwave
assemblies that contain hybrid circuits on ceramic substrates, or circuit boards mounted in a metal substrate .
The cover of the assembly is then sealed with a conductive
sealant. This seal should not be broken, nor repair
attempted . Components in the RF microwave assemblies
are identified with a circuit number when they are referred
to in the calibration procedure (e .g ., C15, C16, and C17 in
A10) . The circuitry within the block is simplified to
illustrate the function of the hybrid assembly .
As previously described in the block diagram description, input signals to the unit can be attenuated in 10 dB
increments up to 60 dB, by AT1 . These signals then pass
through a 1 .8 GHz low-pass filter (FL2) with a stop band
that begins at 2.095 GHz. Signals in the frequency band
from 0 to 1 .8 GHz, then pass through a 3 dB isolation pad
to the 1st mixer.
5-2
The 1st mixer, a double balanced type, converts the
incoming broad spectrum of signals to a 2.095 GHz IF, by
mixing these incoming signal frequencies with the output
of the 1st LO (Al 2) . The 1st LO may be swept and tuned
within the 2.095 GHz to 3.895 GHz band .
The output of the 1st mixer (A11) is isolated by a
traveling wave directional coupler that couples the
2.095 GHz IF signal to a 2.2 GHz LP filter, 2.095 GHz band
pass filter, and into the 2nd mixer in assembly A11 . As
previously described this isolation improves the performance of the 1st mixer and reduces spurious signals.
The 2nd mixer in assembly A11, mixes the output of the
2.2 GHz 2nd LO (in A20) to convert 2.095 GHz down to
105 MHz IF .
The bandpass and center frequency of the 2 .095 GHz
IF is adjusted by the capacitors C15, C16, and C17 (in A10)
and the coupling of the 2nd mixer, in assembly A11 . These
adjustments are performed to obtain a bandpass of
10 MHz that is centered at 2.095 GHz with optimum skirt
shape. The mixer is oriented in the chamber to one of two
balance points to provide the best rejection of spurious
products generated by the 1st LO and 2nd LO .
Band reject filters, consisting of 1/4 wavelength stubs
that are separated 1/4 wavelength, are distributed along
the output transmission lines of the 2nd mixer to the
105 MHz IF . These suppress 2.3 GHz and 4.6 GHz .
The active component for the 2nd LO (in A20) is
transistor Q20. Its collector load is a stripline resonator.
The center frequen^,y of this oscillator and the frequency
span are controlled by an error voltage from the 2nd LO
frequency servo system . The oscillator output is coupled
through a directional coupler to the 2nd mixer and
through a low pass filter to another directional coupler
which is part of the 2nd LO frequency servo system .
The phase lock loop for the 2nd LO (in A20) contains a
99 .2045 MHz oscillator which is multiplied by a factor of
22 . This frequency of 2.1825 GHz is then passed through a
bandpass filter (A40) and mixed in A41 with the output of
the 2nd LO to produce an IF between 16 to 19 MHz.
Bandpass characteristics and center frequency response
of A40 are adjusted by the same procedure that is used to
adjust the bandpass characteristics of assemblies A10 and
Al 1 .
The 16-19 MHz IF output from assembly A41, is also
passed through a 2.3 GHz and 4 .3 GHz filter that is
identical to the filter in assembly A20.
Circuit Description- 7L13
The 1st LO (in A12) is a YIG (yittruim-iron-garnet)
tuned oscillator . YIG is a material that changes its
resonant frequency when it is subjected to a changing
magnetic field . The intensity of this field is controlled by
current through the tuning coil . When the oscillator is
swept, a current ramp from the YIG driver amplifier stage
is applied to this tuning coil . The amplitude of this current
depends on the setting of the FREQ SPAN/DIV selector .
With FREQ SPAN/DIV settings of 100 kHz/Div or less, the
normal state of the 1st LO is to operate in a phase locked
mode at a frequency which depends on the setting of the
TUNING control and some multiple of a 2.21 MHz
reference oscillator.
switch is in the OFF position . The 2nd LO is always phase
locked by a translation phase lock system which is
described below.
Stabilization
The 1st LO phase lock loop contains a reference
oscillator, a pulse generator and sampler, a phase detector, an error amplifier, and a compensating amplifier that
drives thefrequency determining element of the oscillator .
A narrow rectangular pulse from the sampler driver, at
one-half the reference oscillator period, and the output of
the 1st LO are applied to a diode detector . The detector
output charges to the voltage of the pulse plus the
amplitude (at the instant) of the coupled oscillator signal .
The summation of these signals is proportional to the
phase difference between the 1st LO and the reference
oscillator. This voltage is amplified by the error amplifier
and drives the compensating amplifier. The output of the
compensating amplifier maintains a constant phase
difference between the 1st LO and some multiple of the
reference oscillator . While a phase difference may exist,
there is no frequency error. When locked, the long term
frequency stability of the locked oscillator is that of some
multiple of the reference oscillator .
Frequency stabilization is increased and incidental
FM'ing reduced to 10 Hz or less, by a phase lock system
that automatically locks the 1st LO at frequency spans of
50 kHz/Div or less unless the front panel PHASE LOCK
To achieve the required stability, the 2nd LO is
controlled by a translation phase lock oscillator system .
The phase lock loop consists of the circuitry shown in
Fig. 5-1 . The 2nd LO output is applied through a direc-
The front panel 1st LO and 2nd LO OUT jacks (J30 and
J36) provide access to the two oscillator outputs. These
outputs are used by tracking generators . The two ports
must be terminated at all times to prevent reflections back
into the system . Termination plugs P30 and P36 provide
this termination when the ports are not used .
Phase
Lock
and
Frequency
SUM OF : OFFSET,
TUNE CONTROL, AND
MEMORY VOLTAGE
SWP IN
(50 kHz/DIV TO
0.2 kHz/DIV)
Frequency of 2nd LO - 2182 .5 MHz + Frequency of 16-19 MHz VCO .
Fig. 5-1 . Functional block diagram of 2nd LO phase lock circuit or frequency servo system .
5-3
Circuit Description-71
.13
tional coupler to the phase lock loop mixer A41 . It mixes
with the 22nd multiple of a 99 .2045 reference oscillator in
A1400A4, and generates an IF signal between 16 to
19 MHz. The 16 to 19 MHz IF signal is amplified and
applied to a phase detector (A1400A3) where it is compared with the signal from a 16 to 19 MHz oscillator
(A1400A2) . The phase difference is detected, amplified by
the error amplifier (A1400A5), and applied as a control
voltage to the 2nd LO .
When the 1st LO switches from a swept oscillator to
phase locked mode, it may shift in frequency. This shift in
frequency is coupled through to the VCO for the 2nd LO
frequency servo system and pulls the frequency of the 2nd
LO in a direction to offset the frequency shift of the 1st LO .
The center frequency on the display therefore remains
stable . This offset information is provided by the memory
offset digital circuit.
The memory looks at the offset voltage of the 1st LO
before and after phase lock is set, then generates an offset
voltage to apply through a summing amplifier to the 2nd
LO frequency servo system .
The 16 to 19 MHz oscillator consists of an emitter
coupled logic (ECL) IC with a high Q resonant circuit, that
is tuned by a hyperabrupt tuning diode CR1564 . The
frequency of this voltage controlled oscillator (VCO) is
affected by the voltage it receives from the TUNE control
memory circuit, offset voltage, and at spans 50 kHz/Div or
less, the sweep voltage. The control voltages are applied
to both ends of the diode. The summed combination of
offset, tune control, and memory voltage is applied
through pin F to one side of the tuned circuit and the
sweep voltage is applied through pin G, a 30 :1 divider
(R1560, R1562) to the anode of CR1564 .
The sweep voltage comes through the 5 volt regulator
circuit board, where its amplitude is adjusted by the Swp
Gain adjustment R1960 . Additional filtering with C1960,
C1962, is switched in at the slower sweep rates to reduce
the amount of residual line related noise that may be riding
on the sweep line .
The summing amplifier for the tune control, memory,
and offset voltage, is U1735. The memory voltage is
applied through pin AC and the tune control voltage
through pin AN, to the input of the amplifier. The offset
voltage that establishes the center frequency of tuning, is
supplied by VR1720 and a selectable resistor R1725.
Select resistor R1735 sets the gain of U1735 and the
response of the 16 to 19 MHz oscillator to the tune and
memory voltage.
The output of the phase detector (A1400A3) is
amplified by the error amplifier U1715, Q1715, on
A1400A5. The amplifier output drives the collector of the
2.2 GHz oscillator to control its frequency.
5- 4
The sampling generator and driver (A1400A6) are part
of the 1st LO phase lock loop . The output from a
2.1944 MHz crystal controlled oscillator is applied
through Q1820 and Q1825 to a divide-by-two counter
U1825. The 1 .0972 MHz output, from the counter, triggers
avalanche diode CR1832 to generate strobe pulses for the
sampling gate in A50 .
The error voltage from the phase detector is applied
through J1900 and pin S to the input of U1755, which is the
active component for a double-bounded conditionally
stable search amplifier. The double bounding of this
amplifier is achieved with diodes CR1748 and CR1749
(low leakage, temperature stable diodes) which limit the
search amplitude ; and CR1742, CR1744, CR1745, and
CR1746 which limit the holding range of the loop within
the stable gain response range of the phase detector .
The 5 volt regulator board contains ; a 5 volt regulated
supply, phase lock enable relay K1955, sweep gain
adjustment for the 16-19 MHz oscillator, and additional
filtering for the sweep voltage line when the resolution is
30 Hz . The phase lock enable relay K1955 switches the 1 st
LO FM coil from the sweep voltage source to the output of
compensating amplifier U1755 (in the phase lock circuit)
when phase lock is set. Relay K1965 is energized when the
resolution bandwidth is reduced to 30 Hz and adds
additional filtering to the sweep line . Gain adjustment
R1960 calibrates the 5 kHz/Div and less, frequency spans .
YIG Driver, Voltage Memory, and Phase Lock
Logic
4O
The YIG driver consists of a main coil driver and an FM
coil driver . The main coil driver contains an operational
amplifier U2510, and a Darlington transistor Q2520. The
FM coil driver contains amplifier U2530, driving transistors
Q2540 and Q2545. Operation of these drivers is described
under Frequency Tuning and Readout that follows this
title .
The sequence of events required to phase lock the 1st
local oscillator are performed by the phase lock logic
circuit. When phase lock mode is set, the sequence of
events is as follows: 1) The 2nd LO tune control is
engaged and the 1st LO tune control is disengaged . At the
same time the sampling generator for the 1st LO phase
lock loop is enable . 2( At the end of a delay period, the
phase lock enable relay is energized and the search cycle
of the loop begins . 3) At the end of another delay period,
the memory is activated and it looks at the shift the 1st LO
made to reach a lock point. 4) The memory stores this
data, which is later applied to the 2nd LO and summed with
other controlling voltages to shift the 2nd LO frequency an
equivalent amount so it compensates for the shift of the 1 st
LO frequency when it locked .
Circuit Description-71
.13
Pin 1 of P2550 (input to U2560E) is grounded through
the FREQ SPAN/DIV selector when the frequency span is
50 kHz/Div or less . The output of a set-reset flip-flop
(U2565A, U2565C) is low when the PHASE LOCK switch
S125 is ON . The two high inputs at U2565B produce a lowto-enable signal out, which is inverted by U2560A and
applied through pin 4 of P2550 to switch the tuning logic
from the 1st LO tuning potentiometertothe2nd LO tuning
potentiometer R20. This high is also applied through
U2575A, 02570, and 02575 to enable the sampling
generator for the 1st LO phase lock loop .
The low-to-enable signal out of the NAND gate
U2565B, also triggers a mono-stable multivibrator, U2570.
At the end of some delay period, the output of U2570 goes
high . This is compared by NAND gate U2565D, to the high
at the output of U2560A .
The delayed low, out of U2565D, is applied through
buffer amplifier U2575D and energizes phase lock enable
relay K1955, on the 5 V regulator board . The delayed low
signal is also inverted by U2560B and applied through
buffer amplifier U2575B, as a high for the TRACK GEN
connector J70, and through a second buffer, U2575C, to
another delay circuit in the voltage memory .
At this time, the phase lock loop is closed and starts its
search mode . Before one cycle is complete, the 1st LO
should acquire lock . To provide the time necessaryforthe
loop to lock, a second delay is inserted in the sequence
path by a one shot mono-stable multivibrator U2620 and
NAND gate U2625B . At the end of this delay, the outputof
U2625B goes high which is inverted by U2625A and
energizes L2608 to close S2608.
The closing of S2608 contacts allows the capacitor
C2610 to charge to the input error voltage at pin 2 of
P2600 . This error voltage is indicative of the direction and
amount the 1st LO traveled to reach a lock point. The
contacts of S2608 open and the output of 02610 and
02615 goes to the voltage that was stored across C2610.
Memory now sends this compensation voltage to the 2nd
LO and the center frequency on the display remains
stationary .
Frequency
Tuning
Control
and
Readout
Three modes of operation are used to tune the center
frequency: 1) Tune control voltage is summed with the
sweep voltage at the driver input for the main coil of the
YIG oscillator, over frequency spans of 100 MHz/div
through 5 MHz/div. 2) The sweep voltage is removed from
the main coil driver and applied to the FM coil driver for
frequency spans of 2 MHz/div to 0.1 MHz/div . The tune
control voltage is still applied to the main coil driver .
3) The sweep and tune control voltages are removed from
the YIG oscillator driver circuits and applied to the 2nd LO
driver, for frequency spans of 50 kHz/div or less . The 1st
LO is phase locked, providing the front panel PHASE
LOCK switch is on .
Tuning Control OS
The input to P2230-3 (U2200F, U2200D, U2200E) is
high when the phase lock is set (PHASE LOCK switch
S125 on and FREQ SPAN/DIV selector 50 kHz or less).
This condition energizes MP22, which engages the drive
clutch to the tuning potentiometer R20 for the 2nd LO .
MP20 engages when the input to P2230-3 is low, which is
its state for frequency spans of .1 MHz/div (100 kHz/div)
and higher . This drives the tuning potentiometer R22 for
the 1st LO .
The voltage source for the tuning potentiometers is the
outputs of operational amplifiers U2210, 02215, and
U2220, 02225. Zener diode VR2212 sets the inverting
input of U2210 at 9.0 volts, which establishes approximately -9 .2 volts at the emitter of 02215 and
+9 .2 volts at the emitter of 02225 .
The output of U2225 is proportional to the position of
the tuning potentiometer . This voltage is summed with the
sweep voltage at the input to the search marker generator,
then applied through cam 33 (100 MHz/Div or less) to the
YIG driver . The center arm potential of the tuning
potentiometer R20, is applied to the summing point at
U1735, which drives the frequency determing circuits for
the 2nd LO oscillator .
YIG Driver
4O
The do level, out of the center frequency tuning
potentiometer R22, is summed with the sweep voltage at
the inverting input to U2510. U2510 is an operational
amplifier with a Darlington transistor 02520 as the
negative supply source . Increasing the voltage input to the
amplifier increases the current demand from the negative
supply . This forward biases 02520 and increases the
current output so the current through the YIG main coil
increases until the voltage output of R22 balances the
input voltage change to U2510. As the current increases
through the YIG main coil, the frequency of the oscillator
increases.
When the FREQ SPAN/DIV is reduced to 2 MHz or less,
the sweep voltage is removed from the input to U2510 and
applied to the FM coil driver (U2530, 02545 and 02540) .
Current through the main coil is now dependent on thedc
level from the tune potentiometer R22, which sets the
center frequency of the YIG oscillator . K2526 is energized
to shunt the main coil with a filter network consisting of
R2525, C2524 and C2526.
5-5
Circuit Description-71
.13
The FM coil driver is similar to the main coil driver, with
the addition of Q2540 supplying positive current to the FM
coil .
is reduced to 3 MHz. The 3rd mixer converts the 105 MHz
IF to 10 MHz IF, by mixing 105 MHz with the output of a
crystal controlled 95 MHz oscillator .
R2505 adjusts an offset voltage into the summing point
of U2510 so the center frequency of the YIG oscillator can
be calibrated . R2510 and R2530 set the gain of the
operational amplifiers so the frequency span of the YIG
oscillator is calibrated for spans of 100 kHz/div and
higher .
Aperature coupling is used between each section of the
helical resonator. The 3rd mixer is a blanced mixer. 1.85,
and C95 are tuned to the sum of the two input frequencies
(about 95 MHz) . This reflects the upper sideband back
into the mixer and reduces IM signals. C87, R87, L89, and
R241 provide a constant impedance matching circuit to
the input of the 10 MHz IF amplifier.
Frequency Span
O
10 MHz IF Pre-resolution Amplifier and Resolution
1>0
The sweep ramp from either the sweep generator
(U1170), the external sweep source, of the manual control
circuit, is applied through R1254 to the inverting input of
operational amplifier U1250A . This is a voltage ramp from
0 to about 9 volts, which is summed with a do offset
voltage set by R1255 . The output sweep amplitude of
U1250A, is set by R1250 (Swp Gain) so the ramp is a
calibrated 20 volts centered about 0 V. This voltage ramp
drives both the search marker generator (U2580A and
U2580B) and the frequency span attenuator circuit.
Three circuit blocks comprise the resolution circuit; the
10 MHz preamplifier, five selectable resolution filters, and
a post-resolution amplifier. As the resolution bandwidth is
selected, gain compensation is provided to maintain a
constant signal level input to the Function IF amplifier.
The Function IF amplifier is then adjusted so a constant
signal reference level is maintained on the display for
changes of resolution or display modes.
U1250B is the active component of an operational
amplifier whose gain is a function of the input-to-feedback
resistance ratio. This ratio is selected by the FREQ
SPAN/DIV selector S108B. The output voltage ramp of
U1250B is applied to the YIG oscillator main tuning coil
driver U2510, for frequency spans of 5 MHz/Div or more
and to the FM coil for spans of 0.1 MHz/Div and
2 MHz/Div. When the FREQ SPAN/DIV is 50 kHz or less,
this sweep is applied to the phase lock loop forthe 2nd LO .
The signal path through the Resolution Preamplifier
depends on the position of relay K28 . This relay is
energized in all positions of the Gain selector except the
first two (0 dB and 10 dB). When energized, the signal
path is through Q280 and 0290, which has a gain of 20 dB .
Gain of the operational amplifier, containing Q250 and
Q260, is increased by 10 dB when the base of 0270 is
grounded through the gain selector . This occurs every
odd 10 dB step of the selector .
Marker Generator
O
Switching the FREQ SPAN/DIV selectorto MAX SPAN,
closes cam 34 and opens cams 33 and 32 . This routes the
tune control do voltage and sweep voltage output from
U1250A to the input of amplifier U2580A . The YIG
oscillator is now swept its full frequency span and a
marker is generated that is commensurate to the do
potential out of the list LO tune control (R22) .
The output of U2580A causes diodes CR2590 and
CR2592 to switch as the sweep ramp crosses through the
do level setting of the tune control circuit, developing a
negative ditch or marker at the output of U2580B . This
marker is applied to the vertical output circuit to provide
the center frequency marker on the display.
105
MHz
Oscillator
IF
Amplifier,
3rd
Mixer
and
Signals within the 10 MHz bandwidth of the 105 MHz IF,
are amplified by Q85. The output load for Q85, is a three
sectional helical resonator that is tuned so the bandwidth
5-6
Filter Circuits
With the gain selector fully ccw (0 db), the 10 MHz
input signal to T240 is amplified by the IF amplifier Q240
and the operational amplifier that contains Q250 and
0260 . The front panel AMPL (CAL) adjustment R80, sets
the gain of Q240 so a -30 dBm 50 MHz signal, at the RF
INput provides full-screen signal amplitude.
Switching the Gain selector one position cw, grounds
the base of Q270, turning the transistor on, and bypasses
some of the feedback current of the operational amplifier
Q250 . The closed loop gian of the stage is therefore
increased 10 dB . Gain is accurately calibrated by the
10 dB gain adjustment R267 .
Increasing the Gain selector position an additional
10 dB, opens the base of 0270 and energizes relay K281 .
The output of T264 is now switched through Op Amp
Q280-Q290, for 20 dB of additional gain .
Increasing the Gain position to30 dB grounds the base
of 0270, increasing the gain of the preamplifier an
Circuit Description-71
.13
.s
additional 10 dB for a total gain increase through the
preamplifier of 30 dB . As previously described, the relay
K281 remains energized through the remaining four
positions of the Gain selector (total range of the selector is
70 dB, the additional gain variation is provided by the
Function IF) .
The resolution section contains four crystal filters (for
30 Hz to 30 kHz resolution) and a 300 kHz coupledresonator filter . The 300 kHz filter consists of six resonant
sections and an amplifier. Signal path through or around
the filters, is directed and controlled by relays K300, K353,
K354, K355, K356, and K357 . (The 30 Hz filter is located on
YIG Driver Voltage Memory and 30 Hz filter board,
Diagram 8) . These relays are energized as the
RESOLUTION cam switch S108A is switched to positions
that connect the relay armature to the -15 V power
source .
Amplitude adjustments for each filter section establish
a signal output level as the resolution is changed, so the
signal reference level on screen remains constantthrough
the RESOLUTION range . It is important when aligning the
filters, that their center frequency is centered on the
others . This is done by switching in one of the crystal
filters periodically to re-establish the center of the bandpass for the 300 kHz and 3 MHz filters.
The resolution output amplifier provides approximately
15 dB of gain . The gain compensates for loss in sensitivity
through the microwave circuits . The response across the
1 .8 GHz span remains relatively flat (within +1 dB,
-2 dB) .
The 10 MHz IF signal is routed (by K357) through either
a wide filter (3 MHz) or a narrow filter, for additional
shaping and noise reduction. Bandpass of the narrow filter
is between 500 kHz and 600 kHz. K357 is de-energized
when the RESOLUTION is switched from 3 MHz to
0.3 MHz .
YIG Oscillator Power Supply
O8
This supply furnishes a regulated +20 volt and -5 volt
to the YIG oscillator . The +20 volt supply uses +50 volt
supply from the mainframe. R2550 and R2554 set the
reference to the non-inverting input of U2555 . U2555
drives the output transistor 02555. 02565 is a current
limiter for the supply .
Reference level for the -5 volt supply is set by R2583
and R2584 at the non-inverting input to U2585. U2585
drives the output transistor 02580.
30 Hz Filter
18
This filter contains an amplifier, crystal filter, and a
10 dB gain boost circuit. The 10 MHz IF is routed through
the filter when K354 is de-energized, and K2710 is
energized . 02710 and 02715 are emitter coupled
amplifiers . Gain of the amplifier is set by adjusting the
amount of feedback from the output of T2714 to the base
of 02715 . This adjustment is R2730.
An additional 10 dB of gain is provided when the 30 Hz
filter is in the signal path and S27 (10 dB Gain) is closed .
This turns 02735 on and decreases the negative feedback
for the amplifier. Gain is calibrated by adjusting R2735 .
50 MHz Calibrator
O8
The calibrator is a crystal controlled oscillator configured with the crystal in the feedback loop of a multivibrator . Output of the oscillator is calibrated to a
-30 dBm with adjustment R956 . Output impedance is
500.
Function IF Amplifier O9
The Function IF consists of six cascode amplifier cells
or blocks connected in cascade. Each cell operates as a
linear or logarithmic amplifier depending on the display
mode selected to provide the gain characteristics required
for the three display modes of the 71-13. The gain of each
cell is a function of the emitter resistance of the input
transistor. In the Log mode, diodes in the emittercircuitof
the amplifier reduce the gain at a logarithmic rate from
10 kB to 0 dB as the signal level increases.
When the operator depresses the 10 dB/DIV display
button, +15 V is applied through S130A, pin 1 of P135 and
pin 2 of P520 to the anodes of the log diodes ; CR511CR512, CR514-CR515, CR517-CR518, CR521-CR522,
CR524-CR525, and CR531-CR532. These diodes are
forward biased (with no signal input) and the amplifier cell
operates at full gain . As the signal input level increases,
the emitter voltage approaches the bias of the diodes to
turn the diodes off . The amplifiergain therefore decreases
to 0dB .
The gain decreases to 0 dB progressively as the signal
level increases, starting with Q720-0710 and progesses
towards the front end .
In the 2 dB/DIV mode, +15 V is applied to diodes
CR527-CR528 and CR534-CR535 in the emitters of Q680
and Q720 and +15 V is removed from the anode of the
10 dB log diodes so they are now back biased .
5- 7
Circuit Description-71
.13
CR534-CR535, in the emitter of Q720, and CR527CR528 in the emitter of Q680, provide approximately 4 dB
of log gain per amplifier cell . This provides two break
points, at about 4 dBend 8 dB of the gain curve over the
dynamic window . These two break points change the
curve slope sufficiently to shape the curve for 2 dB/DIV .
R737 and R697 set the slope of the curve after the break
point.
The 10 dB and 2 dB/Div Ref Level adjustments R802
and R801, position the linear portion of the log gain curve
(see Fig . 5-2) within the 8 division graticule window .
The 2 dB/DIV and LIN mode displays require at least
70 dB of gain through the analyzer's IF ; therefore, additional stages are switched in to increase the Function IF
gain . S130A is disengaged when the 2 dB/DIV or LIN
mode buttons are pressed . The base of transistors Q570
and Q600 now have a return path to ground, through S83
and pin 4 of P84, in the40 dB or 50 dB positions of the gain
selector . Grounding the base of the transistors, turn them
on and boost the gain through these amplifier cells an
additional 10 dB per cell . Transistors 0630 and Q660 are
turned on when S83 is switched to the 60 or 70 dB
positions.
Gain of the Function IF amplifier, in the LIN and 2 dB
modes, is calibrated at the 40 dB and 60 dB steps by
adjusting R603 and R664 . 0730 is turned on when the LIN
mode is selected and R733 (LIN Ref Lvl) sets the reference
level of the display to the top line of the graticule.
The output signal of Q700 is coupled to a linear
detector . The linear detector consists of Q740 driving the
common emitter amplifier Q750-Q760 with feedback
through C766, the detector diodes CR772-CR771,
resistors R775-R776, and C776 to the input of the
amplifier.
During the positive and negative excursion of the IF
signal, feedback current is supplied through CR772 and
CR771 . This produces a circulating current through the
diodes proportional to the average signal input level. The
negative video output signal is developed across R772R819 and R771 . The video is then applied through a filter
network to the vertical output stages .
Linear Baseline Offset adjustment R803, compensates
for baseline shift when the display mode is switched from
LOG to LIN.
Video Filter, Pulse Stretcher, Baseline Clipper and
Vertical Output
Video signals from the detector, are amplified by
operational amplifier U820B . Its feedback resistance,
R826, is shunted by baseline clamping diodes and fast or
slow video filter circuits that are switched in by U830 and
U840 .
Clamping diodes CR825 and CR826 maintain thevideo
baseline reference by clamping the amplifier input and
output signal levels . CR825 clamps the input of the
amplifier from shifting positive and CR826 clamps the
output at P820-2 so this point cannot shift negative .
The three sections of U840 are connected so they
operate as OR gates to connect C840 in the feedback loop
for U820B . Pulling pin 2 or 3 of P830 low, or closing the
front panel 30 kHz switch S90C, turns one section of U840
on, to connect C840 in the feedback loop . Pin 2 of P830 is
pulled low when the front panel RESOLUTION selector is
switched to the 30 kHz position and pin 3 of P830 is pulled
low when the RESOLUTION is switched to 3 kHz or
300 Hz position .
The three sections of U830 and one section of U840 are
connected to operate as an AND-OR gate . When 300 Hz
(S90A) switch is closed, one section of U830 is turned on
to connect C830 in the feedback loop . Closing both S90A
and S90C (300 Hz and 30 kHz) turns two sections of U830
and one section of U840 on . This connects C830, C832,
and C840 in the feedback loop . The following logic
describes the three filter combinations :
30 kHz = (30 kHz RESOLUTION) OR (3 KHz to 300 Hz
RESOLUTION) OR (C90C closed) .
300 Hz = (S90A closed) .
Fig. 5-2. Log converter curve.
5-8
10 Hz = (S90A) AND (S90C closed) .
O
Circuit Description-71-13
The output of U820B is isolated from summing
amplifier U820C by Op Amp U820D . U820C sums the
video signal with the do level set by the vertical position
control plus the search marker, when present. The output
of U820C drives the positive output for the oscilloscope
interface, the inverting amplifier U820A (which drives the
negative output to the oscilloscope interface) and the
Baseline Clipper circuit.
state is high, 02320 is switched on and positive current
through the interface pin A17 (High) reduces or clips the
crt beam intensity.
The amount of current through 02320 or 02330 is a
function of the Baseline Clipper logic circuit. The common
emitter current switch Q887-0890, switches transistor
0898 off when 0887 is on . Composite video from U820C
will cause the circuit to switch at some level set by the
BASELINE CLIPPER control R96. When Q890 switches
on, Q898 is switched on increasing the current through
02320 to increase the crt beam intensity.
Closing the PULSE STRETCHER switch S90B, turns
0880 on . Current through an emitter follower output
transistor, of amplifier U820D, provides a fast charge path
for C880 on the positive excursion of pulsed video signals
and a long discharge time-constant to stretch the decay
time .
The BASELINE CLIPPER control range isabout50%of
the display amplitude. The CONTRAST control sets the
quiescent current through CR898 which establishes the
contrast between the clipped and unclipped portions of
the display.
The Baseline Clipper circuit consists of a common
emitter current switch (0887-0890) and a logic circuit
(0895-0898) that modulates the Z Axis switching circuit.
The Z Axis switching circuit consists of a current switch
(02320-02330) that is controlled by an exclusive OR gate
(02335 and CR2336). The output of the current switch
drives the Z axis common (pin B17) and the AuxZ axis (pin
A17) .
Frequency Readout
The frequency readout system looks at the frequency
tune control voltage and outputs both a standard readout
signal for the mainframe and a LED readout for the
frequency indicator on the 71-13. The system consists of a
digital voltmeter, driversfor multiplexing the LED readout,
and an A to D converter to drive the mainframe readout
circuits . Fig. 5-3 is a basic functional block diagram .
02335 with CR2336, operate as an exclusive OR, to
gate the state of either interface pin B7 (channel switch) or
A16 (mode info) to the base transistor 02330. When this
INTEGRATOR
IS
FROM
TUNE
POTENTIOMETER
U2145
U2030A
+10 V
CLOCK
0-20,000
COUNTER
MEN
IR
IS
IR
CX
CX
C_X
CF
CFIS
IR
LATCH
LATCHES
STROBED
-V
-10 V REF
\
1 R -1 S
Ic
1 R -1 S
-- CF
Fig. 5-3. Functional block da - 9 -
ONE
DRIVERS
MEN
LED's
of the Frequency Readout circuit.
5-9
Circuit Description-71
.13
The DVM is a precision oscillator . An integrator is
ramped up and down by switching its input currents .
These input currents are switched by commands from a
digital counter and an analog comparator . During one
transition, the count is loaded into latches . This number is
then displayed during the next transition .
The integrator generates an output ram with a timing
sequence proportional to the do level set by the tuning
potentiometer for the 1st LO . The comparator generates a
step signal output when the ramp signal crosses a
reference voltage which triggers the multivibrator.
The counter counts towards 20,000 during the run-up
time of the ramp . When the output of the comparatorsteps
positive, it triggers the flip-flop which loads the count into
the latch and also shifts its number into decoders and
drivers for the LED readout. The new state of the flip-flop
also switches the reference current off and the output
voltage of the integrator ramps down towards 0 volts.
Referring to the schematic diagram 12 ;the voltage
output of the amplifier U2110 is proportional to the input
voltages at pins 2 and 3. The voltage at pin 3 is from the
tuning potentiometer, and ranges from about -9 volt to
+9 volt . An offset voltage can be summed in with this
tuning voltage, for calibration, by adjustment R2135.
Reference current for the integrator U2140, is supplied
by a buffered operational amplifier U2120 and 02120. An
input reference voltage of 11 .7 volts to U2120 is set by
Zener diode VR2115 . This sets the current output of 02120
to a value that is independent of the signal voltages . The
current from this source is steered either to the input of the
integrator or to the power supply by diodes CR2130,
CR2132, and CR2134 .
The voltage state of pin F is set by the multivibrator
U2030A, U2030B in the digital section of the DVM. When
the state is low, CR2132 and CR2134 are off and reference
current is steered through CR2130 to the input of the
integrator . When the state is high, the diodes areturned on
to steer the reference current through R2147 to the power
supply .
As indicated in Fig. 5-3, the reference current is larger ,
than the signal current so the output of the integrator is a
positive-going ramp when it is summed with the signal
current. When the reference current is switched off, the
output of the integrator is a negative-going ramp .
The reference voltage source for the comparator
02115, is the output of operational amplifier U2130. The
11 .7 volt Zener diode VR2115 sets this output at a very
5-10
stable 11 .7 volts. This source provides the reference for
the offset current through R2135 and the reference forthe
negative input of the comparator 02145.
As the positive-going ramp from U2110 crosses the
reference voltage, the output of the comparator steps
high . This triggers the multivibrator U2030A, U2030B and
the voltage at pin F goes high to turn diodes CR2132 and
CR2134 on . The output of the integrator swings past the
reference voltage a slight amount before it starts negative .
When it again crosses the reference potential, the output
of the comparator switches low.
02015, in the digital section of the DVM, is a 0 to 20,000
counter and latch . When it counts to 20,000 or 0, pin 18
goes high . This high is fed back through two inverters
U2000B and U2000C to reset the flip-flop. The resultant
low on pin F turns diodes CR2132 and CR2134 off. The
reference current is again summed with the signal current
and the cycle repeats . The slope of the positive-going
ramp determines the time required for the voltage to reach
the reference that determines the count of the counter.
The clock input to the counter U2015 is generated by
oscillator 02005-02010. The output of the oscillator is
applied through emitter follower 02015, to pin 1 of 02015.
The digit output on pins 4, 5, 6, and 10 is in binary format .
The count in the latch of U2015 is transferred, when the
latch is strobed, to a BCD-to-7 segment decoder (02020)
and through inverter drivers (2000A, U2000D, U2000E,
and U2000F) to a digital-to-analog converter U2065. The
converter sums the digital current input and provides
column sense data (at pin 19) for the readout circuits of the
mainframe .
The digits are displayed sequentially . The seven digit
code for the LED's is applied from decoder 02070;
however, only one digit lights at a time . The command to
light eachh digit is sent out on pins 8, 7, 17, and 22 of
02015, to LED DS2075 . The clock pulse that strobes the
display command from one digit to the next is applied to
pin 11 of U2015 from NAND gate U2030D . When a time slot
goes low, the clock continues to strobe the counter from
one digit to the next (1, 10, 100, 1000) until the corresponding digit display command is gated through AND-NOR
gate U2040. At this time the clock signal through the
NAND gate U2030D is blocked and the column sense
signal current is sent from pin 19 of the D to A converter
02065, to the mainframe readout.
One unit of current differential exists between the LED
readout and the mainframe . Resistors R2020, R2026,
R2133, and R2137 are connected between the respective
time slot line and the sense line to add an additional unit of
current for the mainframe readout circuit.
Circuit Description- 7L13
Uncal Circuit
Reference level calibration of the display depends on
the combination of frequency span, resolution bandwidth,
sweep rate, and video filter bandwidth . It was determined
from the amplitude loss factor equation' ;
a =
1+0.195
2
_
+~e
tB2
that the display is calibrated when the combination of the
above parameters cause the equations ;
Freq Span
0.5 (min B, V) (B) (t)
to equal or exceed 1, where
min B, V = minimum bandwidth of either the resolution
or video filter
B = Resolution bandwidth
t = Sweep time
The multiplication and division of quantities in this
equation can be done by summing the logarithm of the
various parameters. The equation becomes :
log (freq span) - log (0.5) - log (min B, V) - log (t) > 1
By normalizing these parmeters so each term is equals
or is greater than zero, the equation becomes :
. - log
200x 10 6
( Freq Span)
+ log
6
log (10
I (
max
106 or
B
106
V
+
),]
- log (
1
) - 1 .097 > 0
B )
5 x 10-a
The logarithmic summation of these parameters is
performed by an analog circuit and compared against
ground or zero. The resultant indicates if the display is
uncalibrated or calibrated . Fig . 5-4 illustrates the basic
uncal circuit .
I Morris Engelson, "Spectrum Analyzer Measurements (Theory
and Practice)" . Tektronix Concept Booklet No 062-1334-00 .
R1284
NOTE : log [max (B,V)l - max (log B or log V)
If It is positive, and is disconnected from OV current source, the voltage will go positive . If It is negative, the voltage will drop or
go negative. For this reason a ground referenced voltage comparator can be used. The UNCAL indicator lights when It is positive.
Fig. 5-4. Basic functional diagram of the Uncal circuit.
5-11
Circuit Description-71
.13
Sweep Triggering, Sweep Generator and Horizontal
Amplifiers
The sweep ramp is generated by U1170 when it is gated
on by a positive gate signal from U1180. U1180 can be
triggered, or it will automatically recycle after an RC time
interval (set at pin 12) to provide a constant baseline .
Triggering for the sweep generator circuit is supplied
from one of three sources which are selected by S101 . The
selected trigger signal is applied to the input of an
operational amplifier U1010B . The output of U1010B is
summed with the do level set by the LEVEL control R100 .
When the triggering signal amplitude exceeds this do
level, CR1038 is switched on to generate a positive trigger
signal for the trigger input to U1180 . The following occurs
as each source is selected : 1) EXT connects the EXT IN
HORIZ/TRIG connector to the input of operational
amplifier U1010B . 2) INT selects the output of a differential amplifier U1010A, which receives its trigger signal
from the mainframe interface. 3) LINE selects a sample of
the line voltage from the mainframe interface and applies it
to the input of U1010B . FREE RUN (a triggering mode)
grounds the input of U1010B, which sets the output of
U1010C to approximately 0 volt and the input to pin 4 of
U1180 low (approximately -0 .7 volt) . The gate generator
free runs when pin 4 is low.
The positive gate out of U1180 provides the signal for
the sweep generator U1170. The negative gate is amplified
and inverted by 01230 to provide the unblanking gate for
the crt. Pin 15 goes high at the end of the sweep gate and
gates a holdoff pulsethrough U1 160A, U1 160B and 01160
to the mainframe interface.
Current for the SWP indicator light DS1152, is supplied
by transistor 01150. During gate time, in the SGL SWP
mode, the lamp drive from U1180 goes low. This gates a
low out of U1 160B to turn transistor 01150 on . In the SGL
SWP mode, pin 6 of U1180 is grounded so the gate
generator will not run until it has been reset by pushing the
Start button and gating a signal through the NAND gate
U1160C to trigger 01120. This pulls pin 7 of U1180 high
and resets the gate generator so it recycles .
U1170 generates a sweep ramp of 10 volts, with a
duration that depends on the timing current into the
summing point at pin 9. The timing current for the
capacitors C1173, C1174, and C1175 is supplied through
timing resistors R1220, R1221, R1222, and R1224 by
operational amplifier U1120A . Timing combinations are
switched into the circuit by the TIME/DIV selector S104 .
The do level at the input to U1 120A is adjusted by R1200
to compensate for offset of the IC U1170 . The jumper
across P1200 permits a step compensation when U1170 is
replaced and the offset is outside the range of R1200.
Pin 6 of P1160 is an input from a Tracking Generator.
When this input is high, 01215 and 01216 are turned on .
01216 shunts the integrating current for U1170 from
U1 120A to ground . 01215 sets the sweep output line to a
do level that represents center sweep. R1215 adjusts or
calibrates this offset do level of the sweep integrator in
U1170 so the crt beam is centered during the input signal
period from the tracking generator.
The sweep output of U1170 is connected through cam
29 of S104, to the output amplifier U1 050A . Ul 050A drives
U1 040D and both amplifiers supply approximately 0.5 volt
of push-pull drive to the mainframe deflection circuit. Gain
of U1050A is set by SWP CAL adjustment R107 . U1050C
provides a sweep to the mainframe for sweep logic, which
provides the + Sawtooth Output at the front panel of the
7000-Series oscilloscope .
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