Marconi Instruments | TF 1066B/6 | Instruction manual | Marconi Instruments TF 1066B/6 Instruction manual

TM 11-6625-3017-14
TECHNICAL MANUAL
OPERATOR’S ORGANIZATIONAL
DIRECT SUPPORT AND GENERAL SUPPORT
MAINTENANCE MANUAL
FOR
FM/AM MODULATION METER
ME-505 / U
(NSN 6625-00-480-8706)
HEADQUARTERS, DEPARTMENT OF THE ARMY
SEPTEMBER 1981
TM 11-6625-3017-14
TM 11-6625-3017-14
Technical Manual
HEADQUARTERS
DEPARTMENT OF THE ARMY
Washington, DC, 17 September 1981
NO. 11-6625-3017-14
OPERATORS, ORGANIZATIONAL, DIRECT SUPPORT,
AND GENERAL SUPPORT MAINTENANCE MANUAL
FOR
MODULATION METER ME-505/U
(NSN 6625-00-480-8706)
REPORTING ERRORS AND RECOMMENDING IMPROVEMENTS
You can help improve this manual. If you find any mistakes or if. you know of a way to
improve the procedure, please let us know.
Mail your letter, DA Form 2028
(Recommended Changes to Publications and Blank Forms), or DA-2028-2 located in
back of this manual direct to: Commander, US Army Communications and Electronics
Materiel Readiness Command, ATTN: DRSEL-ME-MQ, Fort Monmouth, New Jersey,
07703.
A reply will be furnished direct to you.
CONTENTS
Paragraph
SECTION
0
INTRODUCTION
Scope
Indexes of publications
Forms and records
Reporting of equipment improvement
recommendations (EIR)
Administrative storage
Destruction of army electronics materiel
1
0-1
0-2
0-3
0-1
0-1
0-1
0-4
0-5
0-6
0-1
0-1
0-1
1-1
1-2
1-3
1-1
1-2
1-6
2-1
2-2
2-3
2-4
2-1
2-1
2-2
2-4
GENERAL INFORMATION
Introduction
Data summary
Accessories
2
Page
OPERATION
Installation
Power supply
Controls
Preparation for use
i
TM 11-6625-3017-14
CONTENTS (Continued)
Paragraph
Measuring f.m. deviation
Measuring a.m. depth
Measuring f.m. on a.m.
Measuring a.m. on f.m.
Noise measurements
Oscillator arrangements
Measurement in 1 to 2 MHz range
Asymmetric modulation and carrier shift
Use of l.f. output terminals
Use of I.f. output socket
Crystal selection
F.m. stereo measurements
Phase modulation and telemetry deviation
Stray fields
SECTION
3
2-4
2-5
2-5
2-6
2-6
2-8
2-9
2-9
2-10
2-10
2-10
2-11
2-14
2-14
3-1
3-2
3-3
3-4
3-5
3-6
3-7
3-8
3-9
3-10
3-11
3-12
3-13
3-14
3-1
3-2
3-3
3-3
3-4
3-4
3-4
3-4
3-5
3-5
3-5
3-6
3-6
3-6
4-1
4-3
4-4
4-1
4-1
4-8
5-1
5-2
5-3
5-4
5-5
5-6
5-1
5-1
5-2
5-2
5-8
5-9
MAINTENANCE
Introduction
Performance checks
Cleaning and lubrication
5
2-5
2-6
2-7
2-8
2-9
2-10
2-11
2-12
2-13
2-14
2-15
2-16
2-17
2-18
TECHNICAL DESCRIPTION
System operation
Power unit
Mixer
Local oscillator
I. f. Amplifier
Limiter
Discriminator
Calibrator
Low-pass filters
1st l.f. amplifier
2nd l.f. amplifier
Peak reading meter
A.m. detector
Between-units circuitry on chassis
4
Page
REPAIR
Introduction
Fault location
Waveforms
Realignment
Replacement of sub-assemblies
Replacement of components
ii
TM 11-6625-3017-14
CONTENTS (Continued)
Page
SECTION
6
CIRCUIT DIAGRAM
Circuit notes
6-1
APPENDICES
APPENDIX A
B
References
A-1
Maintenance allocation
B-1
LIST OF TABLES
Table No.
2-1
2-2
2-3
2-4
2-5
4-1
4-2
4-3
4-4
5-1
5-2
Frequency ranges
Spurious deviations with increasing % a.m.
Spurious deviation with increasing a.m. frequency
Crystal selection
Decibel conversion table
Test equipment required
F.m. deviation accuracy
Modulation depth
External modulation
Test equipment required for fault location
Test equipment required for realignment
2-4
2-6
2-6
2-10
2-15
4-4
4-5
4-6
4-7
5-1
5-4
LIST OF ILLUSTRATIONS
Fig. No.
1-1 FM/AM modulation meter, ME-505/U
1-2 Typical demodulation f.m. frequency response with
internal 15 kHz filter
1-3 Typical demodulation f.m. frequency response with
internal 200 kHz filter
1-4 Typical demodulation a.m. frequency response
2-1 Oscillator transit locking arrangement
2-2 Front panel controls
2-3 near panel
2-4 Typical modulation meter noise levels
2-5 Frequency spectrum of f.m. stereo signal with 1 kHz
modulating tone
2-6 Test arrangement for measuring distortion
2-7 Derivation of composite stereo signal showing
unbalance and phase shift errors
2-8 Oscillogram of composite signal
3-1 Block schematic diagram
3-2 Operation of discriminator
3-3 Operation of limiter
3-4 Derivation of standard deviation signal from 400 kHz
oscillator
4-1 Units and parts location (top)
4-2 Units and parts location (bottom)
4-3 Bessel zero measurement
4-4 F.m. noise measurement
iii
1-1
1-5
1-5
1-5
2-1
2-3
2-3
2-7
2-11
2-12
2-13
2-13
3-1
3-2
3-4
3-5
4-2
4-3
4-5
4-7
TM 11-6625-3017-14
CONTENTS (Continued)
LIST OF ILLUSTRATIONS (Continued)
Page
Fig. No.
FO
FO
FO
FO
FO
FO
4-5
4-6
4-7
4-8
5-1
5-2
5-3
5-4
5-5
5-6
5-7
5-8
5-9
5-10
5-11
5-12
5-13
5-14
5-15
5-16
5-17
6-1
6-2
6-3
6-4
6-5
6-6
F.m. distortion measurement
Summation of dB levels
A.m. rejection measurement
Oscillator lubrication points
Oscillograms
Regulated supply measuring points
Location of discriminator output lead
Fitting drive cord
Parts location, mixer TM 7723
Parts location, oscillator board TM 7705
Parts location, doubler and harmonic generator board TM 7706
Parts location, i.f. amplifier ATM 7132
Parts location, limiter ATM 7285
Parts location, discriminator ATM 7780
Parts location, 1st l.f. amplifier ATM1 7223
Parts location, 2nd l.f. amplifier AT[4 8806
Parts location, peak reading voltmeter ATI, 8805
Parts location, a.m. detector ATM 7276
Parts location, calibrator ATM 7620
Parts location, power supply board ATM 7225
Parts location, component board ATM 8742
Chassis inter-unit wiring
Mixer, oscillator and i.f. amplifier
Limiter, discriminator and 1st l.f. amplifier
2nd l.f. amplifier and peak reading voltmeter
A.m. detector and calibrator
Power supply unit
iv
4-7
4-8
4-8
4-9
5-3
5-5
5-6
5-9
5-10
5-11
5-12
5-13
5-14
5-15
5-16
5-17
5-18
5-19
5-20
5-21
5-22
Located
back of
Manual
TM 11-6625-3017-14
SECTION 0
INTRODUCTION
0-1.
SCOPE
This manual describes F.M./A.M. Modulation Meter ME-505/U (Marconi Model TF 2300A) (fig. 1-1) and provides
operation and maintenance instructions. Throughout this manual, ME-505/U is referred to as Modulation Meter type
2300A.
0-2.
INDEXES OF PUBLICATIONS
a. DA Pam 310-4. Refer to the latest issue of DA Pam 310-4 to determine whether there are new editions,
changes, additional publications or modification work orders pertaining to the equipment.
0-3.
FORMS AND RECORDS
a.
Reports of Maintenance and Unsatisfactory Equipment. Maintenance forms, records, and reports which are
to be used by maintenance personnel at all levels of maintenance are listed in and prescribed by TM 38-750.
b.
Report of Packaging and Handling Deficiencies. Fill out and for ward SF 364 (Report of Discrepancy (ROD))
as prescribed in AR 735-11-2/DLAR 4140.55/NAVMATINST 4355.73/AFR 400-54/MCO 4430.3E
c.
Discrepancy in Shipment Report (DISREP) (SF 361). Fill out and forward Discrepancy in Shipment Report
(DISREP) (SF 361) as prescribed in AR 55-38/NAVSUPINST 4610.33B/AFR 75 - 18/MCO P4610.19C and DIAR 4500.15.
0-4.
REPORTING OF EQUIPMENT IMPROVEMENT RECOMMENDATIONS (EIR)
EIR’s will be prepared using DA Form 2407, Maintenance Request Form. Instructions for preparing EIR’s are provided in
TM 38-750, The Army Maintenance Management System. EIR’s should be mailed directly to Commander, US Army
Communications and Electronics Materiel Readiness Command, ATTN: DRSEL-ME-MQ, Fort Monmouth, New Jersey,
07703. A reply will be furnished directly to you.
0-5.
ADMINISTRATIVE STORAGE
Administrative storage of equipment issued to and used by Army activities shall be in accordance with TM 740-90-1.
0-6.
DESTRUCTION OF ARMY ELECTRONICS MATERIEL
Destruction of Army electronics materiel to prevent enemy use shall be in accordance with TM 750-244-2
Procedures for Destruction of Electronics Materiel to Prevent Enemy Use (Electronics Command).
0-1
TM 11 6625-3017-14
SECTION 1
GENERAL INFORMATION
1.1 INTRODUCTION
The TF 2300A Modulation Meter is primarily for
measurement of f.m. deviation but it also measures a.m.
depth. With its wide range of deviation frequency,
modulation bandwidth and carrier frequency, this
instrument is suitable for application to fixed and mobile
point-to-point communications, broadcasting, telemetry
and multi-channel link equipment in the h. f., v. h. f.
and u. h. f. bands. Distortion and channel separation
tests on f.m. stereo receivers and transmitters can also
be made.
normally made by means of the meter readout, i. f. and
demodulated outputs are available at the front panel for
examination or analysis.
Positive and negative f.m. deviation can be
measured in ranges from 1. 5 kHz to 500 kHz full- scale
at modulation frequencies between 30 Hz and 3.4 kHz
on the 1.5 kHz deviation range, and 30 Hz and 200 kHz
on all other deviation ranges. A.M. depth can be
measured up to 95% in a 30 Hz to 15 kHz modulation
bandwidth. Either f.m. or a.m. can be measured in the
presence of the other. Although measurements are
The instrument can be operated from mains power
or a nominal 24 V battery. Voltage regulation eliminates
transformer tap changing except between 115 V and 230
V ranges. On battery, the regulation compensates for
battery voltage variations between 21.5 and 30 V.
Transistorized circuits consuming little current give
reasonable length of operation on battery for mobile
purposes.
Spurious a.m. and f.m. due to hum and noise are
kept to a level insignificant for most applications but,
where required, crystals can be switched in to control the
local oscillator, or an external local oscillator may be
used. The instrument can be operated without a local
oscillator for measurements in the 1-2 MHz range.
Fig. 1-1. FM/AM Modulation Meter ME-505/U
1-1
TM 11-6625-3017-14
1.2 DATA SUMMARY
Characteristics
Performance
Supplementary information
R.F. input
Frequency range:
4 MHz to 1000 MHz.
Sensitivity:
Less than 20 mV between
4 and 250 MHz.
Typically less than 10 mV.
Less than 50 mV between
250 and 500 MHz.
Typically less than 25 mV.
Less than 100 mV between
500 and 1000 MHz.
Typically less than 50 mV.
Maximum input:
3 V r. m. s. (200 mW).
Input impedance:
Nominally 50 Q.
Local oscillator
Variable frequency operation:
The internal oscillator covers
two ranges 5. 5 to 11 MHz and
22 to 44 MHz, harmonics being
used for other local oscillator
frequencies.
Calibration accuracy:±
3%.
Crystal operation:
Up to three crystals within the
frequency range 22 to 44 MHz
may be fitted for use with input
frequencies between 20. 5 and
1000 MHz.
External oscillator input required
approximately 200 mV.
I.F.output
Frequency:
1.5 MHz.
Amplitude:
Between approximately 250 and
750 mV e. m. f.
Output impedance:
Nominally 10 kΩ.
F.M. measurement
Carrier frequency range:
4 to 1000 MHz.
1-2
Usable up to 1.6 GHz with internal
oscillator and at higher frequencies
with an external oscillator.
TM 11-6625-3017-14
Characteristics
Performance
Deviation range:
Six ranges with full scale
indications of 1.5, 5, 15, 50,
150 and 500 kHz. Positive or
negative deviation indication
selected by a switch.
Modulation frequency:
30 Hz to 200 kHz on all ranges
except the 1. 5 kHz deviation
range which is limited to 30 Hz
to 3.4 kHz.
Accuracy:
+3% of f. s. d. for deviations up
to 500 kHz and modulating
frequencies between 30 Hz and
150 kHz, ±5% of f. s.d. on the
1.5 kHz deviation range.
+10% of f. s. d. for deviations up
to 500 kHz and for modulating
frequencies between 150 kHz and
200 kHz.
A.M. rejection:
Additional deviation error
typically less than 150 Hz in a
15 kHz bandwidth when the a. m.
depth is 80% and the modulating
frequency is 1 kHz.
Inherent noise:
Deviation less than -70 dB relative
to a level of 50 kHz deviation in a
15 kHz bandwidth when the local
oscillator is crystal controlled.
Supplementary Information
Typically +5% of f. s. d.
A.M. measurement
Carrier frequency range:
4 to 350 MHz.
Mod. depth range:
Two ranges with full-scale
indications of 30% and 100%.Peak
and trough indications selected by
a switch.
Accuracy:
+3% of f. s. d. for modulating
frequencies between 30 Hz and
15 kHz, and modulation depths
up to 80%. +5% of f. s. d. for
modulating frequencies between
30 Hz and 50 kHz, and modulation
depths up to 95%
1-3
Maximum usable reading: 95%.
TM 11-6625-3017-14
Characteristics
Performance
Supplementary information
L.F. output
Frequency range:
30 Hz to 200 kHz with switchable
15 kHz low pass filter on f. m.
except on the 1.5 kHz deviation
range.
30 Hz to 50 kHz on a. m.
Typical response curves are
shown in Figs. 1-2, 1-3,
and 1-4.
De-emphasis:
Switchable to 0, 50 or 75 ’Sec.
Output level:
Nominally 0 dBm into 600 Q when
meter reads full-scale, except on
the 1.5 kHz deviation range when
the output is nominally -10 dBm.
On the 1.5 kHz deviation range the
de-emphasis operates on the meter
as well as the demodulated output.
Distortion:
Less than 0.2% for f.m. Deviations
up to +75 kHz and modulating
frequencies up to 15 kHz.
Typically less than 0.1%.
Less than 0. 3% for f.m. Deviations
up to +300 kHz and modulating
frequencies up to 25 kHz.
Typically less than 0.2%.
Less than 3%O for f.m. deviations
up to ±500 kHz and modulating
frequencies up to 200 kHz.
Typically less than 2.0%.
Less than 1% for a.m. depths up
to 60%.
Typically less than 0.5%.
Less than 2% for a.m. depths up
to 90%.
Typically less than 1.0%.
A.C. mains
90 Vto 130 V or 180 V to26V.
45 to 500 Hz, 15 VA.
External battery:
21.5 to 30 V d. c.
Dimensions and weight
Height
19 cm
(7 3/4 in)
Power requirements
320 mA at 24 V d. c.
Width
47 cm
(18 2 in)
1-4
Depth
36 cm
(14 1 in)
Weight
13.6 kg
(30 lb.)
TM 11-6625-3017-14
Response curves for meter and 1. f. output with de-emphasis off.
Fig. 1-2. Typical demodulated f.m. frequency response with internal 15 kHz filter.
Fig. 1-3. Typical demodulated f.m. frequency response with internal 200 kHz filter.
Fig. 1-4. Typical demodulated a.m. frequency response.
1-5
TM 11-66253017-14
1.3 ACCESSORIES
Supplied
Extension Board type TM 7926; for use when servicing printed
circuit boards.
Mains Lead type 23424A158
Optional
Rack Mounting Conversion Kit type TM 8340.
Protective Cover type TM 7958/3; for protection of the front
panel during transit.
Oscillator crystals. Marconi type Q01670 series; frequencies
as specified in Section 2.15.
Shielded Adapter, type TB 39868 (Greenpar type GE 51002) for
converting OUTPUT terminals to BNC coaxial socket.
R. F. Fuse Unit, type TM 9884.
If you need to use cleaning fluids
while working on this Modulation
Meter, observe the following warning:
WARNING
Adequate ventilation should be provided while using TRICHLOROTRIFLUOROETHANE. Prolonged
breathing of vapor should be avoided. The solvent should not be used near heat or open flame; the
products of decomposition are toxic and irritating. Since TRICHLOROTRIFLUOROETHANE dissolves
natural oils, prolonged contact with skin should be avoided. When necessary, use gloves which the
solvent cannot penetrate. If the solvent is taken internally, consult a physician immediately.
1-6
TM 11-6625-3017-14
SECTION 2
OPERATION
2.1 INSTALLATION
The Modulation Meter type TF 2300A is available in
two versions: with a case for bench mounting, or with a
dust cover for rack mounting.
The latter version,
designated TF 2300AR, fits a standard 19 inch rack.
the clip. A 6 BA screw, otherwise housed in a second
hole to one side of the clip in the end plate is inserted
through the clip and tightened down for long journeys,
including delivery.
Before inserting the TF 2300AR into a rack, slides or
runners should be fitted to the rack to support the
instrument and aid location.
To reach the clip, release the four screws at the corners
of the oscillator front panel and slide the oscillator partly
out. For short journeys, the carriage need not be locked
if the instrument is placed upright on a layer of padding,
preferably with the tuning mechanism set to the high
frequency limit of its travel.
Transit precautions
To prevent damage being caused to the moving parts by
shocks or vibrations in transit, a clip as shown in Fig. 2-1
is fitted. The tuning mechanism consists of a carriage
running on a worm screw turned by the control knob; the
carriage is mechanically coupled to ferrite tuning slugs in
the variable inductors. The transit clip locks the carriage,
and this must be released before the oscillator can be
used. At the high frequency end of carriage travel, a
tapped hole in the top of the brass carriage comes in line
with a hole in
Remove the locking screw before attempting to use the
oscillator.
2.2 POWER SUPPLY
The modulation meter may be used with a. c. mains or
batteries.
2.2.1
Mains supply, 110-230 V
The socket of the lead provided with this instrument
fits into the plug on the rear panel. The other end of the
lead must be fitted with a plug by the user. The three
conductors are provided with identification sleeves for
this purpose, as follows:
Color
Connection
Brown
Line
Blue
Neutral
Yellow/GreenEarth
Sleeve
Black
Yellow
Symbol
WhiteN
(Green)
Before plugging in to the mains supply, check that
the fuse rating and mains voltage setting are correct.
For voltages around 230 V, a 100 mA fuse is fitted; for
110 V, this must be changed to 160 mA. Check that the
h. t. fuse is 500 mA and note that it is a quick-blow type.
To change the mains voltage switch setting, remove the
L-shaped
Fig. 2-1. Oscillator transit locking arrangement
2-1
TM 11-6625-3017-14
lock-plate secured by two screws above the switch, slide
the switch button into its other position (as shown on the
panel), reverse and replace the lock-plate to hold the
button in its new position. No other adjustment is
needed.
(5)
CRYSTAL switch.
Selects crystal required.
Switch to OFF when not crystal controlled.
(6)
RANGE switch. Selects internal local oscillator
ranges as shown beside tuning dial, or external
oscillator.
(7)
R. F. IN socket.
under test.
(8)
I. F. OUT socket. Type BNC. Connect to
counter for measuring carrier shift or to
oscilloscope for viewing unfiltered a.m.
envelope. Output is 1.5 MHz at about ½ V.
(9)
LEVEL control. Adjusts attenuation of signal
input at R. F. IN socket.
(10)
SET A.M. level control. Adjust for SET reading
on meter when Function selector is at SET A.
M.
(11)
Function switch.
Selects setting up and
measuring conditions on f.m. and a.m. Numbers
show normal sequence of settings.
(12)
A. M./DEV RANGE switch. Selects full-scale
meter range, six for f. m., two for a. m.
Switch the MAINS -BATT switch Lo MAINS.
2.2.2
Type BNC.
Accepts signal
Battery operation
The modulation meter also works on 24 V batteries. A
suitable supply would be a 24 V positive earth vehicle
battery, on or off charge. Negative earth systems must
not be used on any account, since the case of the
instrument and its coaxial connections would be live. If a
positive earth supply is not available, use dry cells. Six
4.5 V batteries, e. g. Exide type H30 or 3DT9, giving 27
V initially, should give several hours of service before
their output drops below 21.5 V. This is equivalent to
several weeks in normal use provided that the instrument
is switched off as soon as the measurement is
completed. Current drain is 350 mA approximately.
Observe correct polarity when connecting batteries to the
back panel terminals; left is positive.
Switch the MAINS-BATT switch to BATT.
2.3 CONTROLS
(13)
The following outline of control functions is intended
for reference purposes. Until you are familiar with the
instrument, use the operating procedures detailed in later
sections.
MAX MOD FREQ switch. Selects modulation
bandwidth in f.m. measurements.
(14)
OUTPUT terminals.
Provide demodulated
output for connection to extra-sensitive meter,
wave analyser etc.
(1) Oscillator tuning dial. Shows effective internal local
oscillator frequency.
(15)
(2) OSCILLATOR TUNE controls. (Outer: coarse - inner
: fine). Adjust for dial reading 1.5 MHz above signal
frequency. Inoperative when using external local
oscillator.
Meter. Reads % a.m. depth and f.m. deviation.
R.F. LEVEL arc applies to position 1 of Function
switch, and SET mark to the four SET positions.
(16)
SET CAL F.M. preset. Standardizes deviation
measuring accuracy. Adjust for SET reading on
meter with Function switch at SET CAL.
(3) CRYSTAL sockets.
Accept style D miniature
crystals for local oscillator control.
(17)
DE-EMPHASIS switch. Applies deemphasis to
demodulated signal at OUTPUT terminals.
Does not affect meter readout, except on 1.5
kHz deviation range.
(18)
SUPPLY switch. Shows red segments when on.
Works on both mains and battery operation.
(4) EXT OSC socket. Type BNC: Accepts external
local oscillator signal of about 100 mV.
2-2
TM 11-6625-3017-14
Fig. 2-2. Front panel controls
Fig. 2-3. Rear panel
2-3
(19)
Supply plug. Accepts Mains Lead type TM 7052
for a.c. operation.
(20)
H.T. fuse. 500 mA quick-blow type.
(21)
Mains fuse. 100 mA (for 230 V a.c.) or 160 mA
(for 110 V a.c.) slow-blow type.
(22)
Mains voltage selector. 230 V position for 190260 V, 110 V position for 90-130 V. Reverse
locking plate when changing range.
(23)
Battery terminals.
positive earth.
(24)
MAINS/BATT switch. Select MAINS for a. c.
supply to plug, BATT for d.c. supply to terminals.
21-30 V d.c.
floating or
TM 11-66253017-14
TABLE 2.1.
2.4 PREPARATION FOR USE
Frequency ranges
It is helpful in reading these instructions and in using
the instrument until completely familiar with its operation,
to remember that where a control or switch position is
marked SET, the control should be adjusted to make the
meter read on the line marked SET.
RANGE switch
setting
1-2
Before commencing measurements:
3-4
(1)
Check the mechanical zero of the meter and
adjust, if necessary, by means of the screw.
(2)
Turn the LEVEL control towards minimum
(counter-clockwise).
(3)
Connect the signal to be tested to the R. F. IN
socket at a level which, operating into50 1, will
develop a voltage within the limits given in
section 1.2 under ’R. F. input’ .At the highest
carrier frequencies the shortest possible input
lead should be used or an external 50 f matching
attenuator.
5-8
EXT
CAUTION Inputs greater than 3 V r. m. s. May damage
the attenuator. If in doubt, use an external attenuator.
(4)
Set the A.M. /DEV RANGE switch (below the
meter) to suit the expected deviation of the
signal under test.
(2)
Set the MAX MOD FREQUENCY switch to 200
kHz unless the modulating frequency is less than
15 kHz. If so, switch to 15 kHz in order to obtain
the best signal-to-noise ratio.
(3)
Set the DE-EMPHASIS switch as required. Its
setting has no effect on the internal meter
reading unless the A.M. /DEV RANGE switch is
in the 1.5 kHz deviation position. The deemphasis is effective on the demodulated signal
at the OUTPUT terminals.
2-4
-
R.F. input freq.
MHz
5.5 -11
11 - 22
22-44
44.-.88
88-176
176- 352
352-704
701.5-1001.5
4.0 - 9.5
9.5 - 20.5
20.5 - 42.5
42.5 - 86.5
86.5 - 174.5
274.5 - 350.5
350.5 - 702.5
700 - 1000
F+ 1.5
F
Set the oscillator RANGE switch in accordance
with table 2.1. For detailed instructions on
oscillator arrangements, see section 2.10. In
this section, it is assumed that the internal local
oscillator will be used.
(5)
Set the Function switch to TUNE OSCILLATOR
AND ADJUST LEVEL. Adjust the OSCILLATOR
TUNE dial to a frequency 1.5 MHz above the
carrier. Tune for peak meter deflection, and
then adjust LEVEL for a meter deflection in the
black R. F. LEVEL arc, preferably near the top
end for best signal-to-noise ratio.
(6)
Set the Function switch to F.M. SET FREQ.
Slightly readjust the OSCILLATOR TUNE control
until the meter deflects to the SET line. Avoid
spurious settings - the correct one is the closest
to the original setting obtained in (5).
(7)
Set the Function switch to DEV + and DEV-.The
demodulated peak frequency deviations above
and below the carrier frequency may be
measured on the meter or viewed on an
oscilloscope connected to the OUTPUT
terminals.
Read the meter on the scale
corresponding to the setting of the A. M./ DEV
RANGE switch.
Note
If unequal readings are obtained, distortion in the
equipment under test is indicated.
See section 2.12.
(8)
Before carrying out a series of measurements,
and from time to time during measurements,
After carrying out the preparation procedure in
section 2.4:
(1)
1
2
3
4
5
6
7
8
Osc. freq.
MHz
(4)
Turn the SUPPLY switch clockwise so that the
red segments show.
2.5 MEASURING F.M. DEVIATION
Range
TM 11-6625-3017-14
switch to SET CAL and check that the
meter reads SET. If necessary, adjust the
f.m. calibration by inserting a screwdriver in
the SET CAL F.M. preset and adjusting
until the meter reads SET.
CAUTION
(4)
Do not attempt to SET CAL on the 1.5 kHz
f.m. deviation range.
Noise in f.m.
measurements
(5)
To accommodate signals with up to 100%
amplitude modulation the maximum r. f. input level, as
indicated by full-scale deflection on the black meter arc,
is set at 6 dB below the maximum amplitude which the i.
f. amplifier can handle. When making measurements
on f.m. signals including f.m. noise, and f.m. on a. m.,
this extra level capability of the i. f. amplifier can be
used with advantage to reduce the internally generated
noise to a minimum. This is useful when measuring
noise on signal sources or when measuring deviations in
the 5 kHz range on the 200 kHz bandwidth so that errors
due to noise are minimized.
(6)
(7)
The optimum r. f. level is set by monitoring the i.
f. signal at the I. F. OUT socket and adjusting the r. f.
input level for the maximum undistorted i. f. signal.
Alternatively, if no means of monitoring the i. f. signal is
available, it is sufficient to increase the r. f. input level
until the noise signal being measured is at a minimum, or
if deviation is being measured, until the deviation reading
is at a minimum.
2.7
After carrying out the preparation procedure in
section 2.4:
Set the A. M./DEV RANGE switch (below the
meter) to the 30% or 100% a.m. depth range
according to the expected modulation depth of
the signal under test.
(2)
Set the oscillator RANGE switch in accordance
with table 2.1. For detailed instruct- ions on
oscillator arrangements, see section 2.10. In
this section, it is assumed that the internal local
oscillator will be used.
(3)
Set the Function switch to TUNE OSCILLATOR
AND ADJUST LEVEL.
Adjust the OSCILLATOR TUNE dial to a frequency of 1.5 MHz
above the input frequency. Tune for peak
MEASURING F.M. ON A.M.
To measure the spurious f.m. on an amplitude modulated source, proceed as for f.m.
measurement, section 2.5.
A certain amount of spurious f.m. is introduced by
the instrument itself.
When the carrier is deeply
modulated, at high modulating frequencies, this should
be taken into consideration, but below 40% depth in the
audio range of frequencies the spurious deviation is not
very significant. At 80% depth and 1 kHz frequency, the
maximum spurious deviation is typically less than 150 Hz
referred to the 15 kHz bandwidth.
2.6 MEASURING AM. DEPTH
(1)
deflection and then adjust LEVEL to give a meter
deflection in the black R. F. LEVEL arc,
preferably towards the lower end for best mixing
and hence minimum distortion.
Set the Function switch to A.M. - SET FREQ.
Slightly readjust the OSCILLATOR TUNE control
until the meter deflects to the SET line. Avoid
spurious settings - the correct one is the closest
to the original setting obtained in (3).
Set the Function switch to SET A.M. Adjust the
adjacent SET A, M. control until the meter reads
on the SET line. Note that this setting can be
done with or without modulation since the
adjustment is to the mean level of the i. f.
signal. However, appreciable even harmonic
distortion can affect the setting accuracy and, in
such circumstances, it is preferable to set up
without modulation.
Set the Function switch to A.M. PEAK. Read the
percentage modulation depth at the peak
Set the Function switch to A.M. TROUGH. Read
the percentage modulation depth at the trough.
When the peak and trough readings are
unequal, distortion is present in the input signal.
Tables 2.2 and 2.3 give typical results which should
be used for general guidance purposes only .
2-5
TM 11-6625-3017-14
TABLE 2.2
2.9 NOISE MEASUREMENTS
By connecting an external meter to the OUTPUT
terminals, noise measurements limited only by the noise
level generated within the instrument can be made. The
internal meter, being peak reading, is not suitable for
measuring noise and, ideally, an r.m.s. responding meter
should be used. However, sufficiently accurate results
are usually obtained with an average reading meter by
applying the appropriate correction factor.
Spurious deviations with increasing % a.m.
1. LEVEL control set for meter reading at top end of arc.
2. A.M. frequency = 1 kHz
Spurious deviation
A.M.
15 kHz bandwidth
200 kHz bandwidth
Typical meters which can be used are as follows:
30
75 Hz
750 Hz
80
150 Hz
2 kHz
(a)
R. M. S. valve voltmeter capable of measuring
to the necessary accuracy (1% deviation on any
range is approximately 7.75 mV). Errors due to
crest factor and zero shift can be avoided by
operating the meter at mid-scale by means of an
attenuator.
(b)
Marconi Instruments Sensitive Valve Volt- meter,
type TF 2600.
(c)
Marconi Instruments Distortion Factor Meter,
type TF 2331.
(b)
and (c) are average reading and a correction of
+1 dB should be applied.
(1)
The modulation meter has two selectable f.m.
bandwidths and the appropriate filter must be
selected when making the test.
TABLE 2.3
Spurious deviations with increasing a.m. frequency
1. LEVEL control set for meter reading at top
end of arc.
2. A.M. depth = 80%.
Spurious deviation
A.M. freq.
15 kHz bandwidth 200 kHz bandwidth
1 kHz
150 Hz
2 kHz
10 kHz
2 kHz
3 kHz
-
7 kHz
100 kHz
A capacitor should be connected across the
OUTPUT terminals - 0.
014 ~F for the 15 kHz
bandwidth, or 0. 0013 ,F for 200 kHz. These corrective
capacitors are necessary because of the design of the
filters (see section 3. 9).
2.8 MEASURING A.M. ON F.M.
The modulation meter may be used to indicate amplitude
modulation in a frequency modulated signal, provided
that the deviation is less than 100 kHz The procedure is
that of a.m. measurement, section 2.6.
For optimum results in the 15 kHz bandwidth position
a low-pass filter as shown below should be used
between the OUTPUT terminals and the external meter
instead of the capacitor.
In general, the spurious a.m. Indication will be
proportional to the deviation. The i. f. amplifier is set up
for optimum phase response for f.m. deviation
measurement rather than a maximally flat response for
measuring a.m. on f.m.
Below 100 kHz deviation, the internally generated
spurious a.m. is less than 2% approximately.
2-6
TM 11-6625-3017-14
For noise measurements in other bandwidths
select the MAX MOD FREQUENCY 200 kHz band- width
setting and use a similar type of low-pass filter designed
for the required cut-off frequency.
(2)
The output of the modulation meter is 0. 775 V
into 600 n for full-scale deflection on the internal
meter.
(3)
For measurements in the r. f. range 22 MHz to
1000 MHz the local oscillator must be crystal
controlled if lowest possible internally generated
noise is required. Thus, a crystal suitable for the
appropriate frequency must be available. This is
not a requirement below 22 MHz, where the
internal noise of the oscillator is sufficiently low
to make crystal control unnecessary.
(4)
width in which the measurement is to be made
and the carrier frequency.
In the 200 kHz bandwidth, there is little advantage in
using crystal control below 500 MHz.
In both
bandwidths, crystal control will eliminate oscillator
microphony and therefore may be advantageous in
conditions of vibration or high acoustic noise levels.
F.M. noise
The curves given in Fig. 2-4 show typical noise
levels produced by free-running and crystal
controlled oscillators over the r.f. range of the
instrument. In the 15 kHz bandwidth, below 70
to 100 MHz, there is insignificant difference in
respective noise levels.
Above 100 MHz,
however, the noise level free-running increases
progressively with frequency, whereas under
crystal control the level remains nearly constant.
The necessity to use crystal control depends on
the noise level of the equipment under test and,
as shown by the curves, the band-
(1)
Connect an external meter to the OUTPUT
terminals. Apply r. f. input at a suitable level.
(2)
Adjust the OSCILLATOR TUNE dial to a
frequency 1.5 MHz above the carrier and tune
for peaking, as in section 2. 5(5). Then adjust
LEVEL to the top end of the black arc on internal
meter. Switch to 15 kHz or 200 kHz MAX MOD
FREQUENCY setting, thus selecting the
required low-pass filter in the modulation meter.
(See also Sect. 2.5 - Noise in f.m.
measurements. )
(3)
Switch to position F.M. SET FREQ and adjust
the oscillator until meter reads SET.
(4)
Switch to crystal control and check that the
meter still reads near to the SET mark - the
Fig. 2-4. Typical modulation meter noise levels
2-7
TM 11-6625-3017-14
actual reading will depend on frequency tolerances in the
source and local oscillator output. Switch to DEV +.
(7) Remove the modulation from the signal under test.
Turn the A.M./DEV RANGE switch to its most sensitive
range and then increase the sensitivity of the external
meter to give a convenient reading. Record the new
level, which is given by the reading on the external meter
plus 10 dB for each step of the A. M./ DEV RANGE
switch.
(8) The signal-to-noise ratio is given by the difference
between the levels measured in (6) and (7).
(5) Modulate the carrier to the reference deviation and
select the appropriate range on the A. M./DEV RANGE
switch.
(6) Read the external meter and record the dB level.
(7) Remove the modulation from the signal under test.
Turn the A.M. /DEV RANGE switch to its most sensitive
range and then increase the sensitivity of the external
meter to give a convenient reading. Record the new
level, which is given by the reading on the external meter
plus 10 dB for each step of the A.M. / DEV RANGE
switch.
2.10
OSCILLATOR
OPERATING NOTES
ARRANGEMENTS
AND
The same procedure applies for both f.m. and a.m.
measurements. The basic requirement is for a stable
frequency source 1.5 MHz higher than the signal under
test, and this can be obtained from three sources:
(a) The internal permeability-tuned variable oscillator
usable at all frequencies between 4 and 1000 MHz.
(b)
The internal crystal controlled spot-frequency
oscillator, usable with selected crystals over the range of
20 to 1000 MHz.
(c) An external oscillator with an output of 100 mV
across 50 U.
(8) The signal-to-noise ratio referred to the selected
bandwidth in which the measurements were made is
given by the difference between the levels measured in
(6) and (7).
A.M. noise
(1) Connect an external meter to the OUTPUT terminals.
Apply r. f. input at a suitable level.
2.10.1 Variable oscillator
(2) Adjust the OSCILLATOR TUNE dial to a frequency
1.5 MHz above the carrier and tune for peaking, as in
section 2.6
Choose the appropriate range on the RANGE switch.
(3). Then adjust LEVEL to the top end of the black arc
on internal meter. (3) Switch to position A.M. SET FREQ
and adjust the oscillator until the meter reads SET.
Rotate the TUNE dial with the coarse and fine
controls to a setting 1.5 MHz above the frequency of the
input signal. Note that there are meter peaks 1.5 MHz
above and below the carrier frequency; always tune the
oscillator to the higher frequency for correct polarity
sense of the Function switch.
Check that the CRYSTAL selector is at OFF.
(4) Switch to crystal control and check that the meter still
reads near to the SET mark - the actual reading will
depend on frequency tolerances in the source and local
oscillator output. Switch to A.M. PEAK.
Adjust the fine control from time to time, to bring
the meter reading to the SET mark when switched to the
SET FREQ position. It is permissible to tune to another
internal oscillator harmonic as this will not affect the
readings obtained.
(5) Modulate the carrier to the reference depth and
select the appropriate range on the A. M./DEV RANGE
switch.
(6) Read the external meter and record the dB level.
2-8
TM 11-6625-3017-14
The oscillator takes about two minutes to
stabilize after turning on, but this is only of any
significance at very high frequencies.
2.10.4 Use above 1000 MHz
It is possible to use the instrument above 1000
MHz using internal or external oscillator.
With either the variable or crystal controlled
oscillator, higher harmonics are sufficiently present to
cover the range 1000 to 1600 MHz without loss of
sensitivity. For 1000 to 1400 MHz, use range 7 with a
scale indication of half the wanted frequency (500 - 700
MHz). Similarly, for 1400 to 1600 MHz use part of range
8 (700 - 800 MHz).
Using a suitable external oscillator the carrier
frequency range can be extended to about 2500 MHz,
but the sensitivity may deteriorate.
2.10.2 Crystal-controlled oscillator
Plug in a crystal of the required frequency as
selected in section 2.15.
Select the appropriate position on the RANGE
switch and set the oscillator dial to the crystal frequency.
Set the CRYSTAL selector to the crystal position
number.
Slight tuning on position TUNE OSCILLATOR of
the. Function switch may be necessary to obtain
maximum sensitivity at the higher frequencies. DQ not
tune far off the original setting to avoid any possibility of
mode jumping.
2.11
MEASUREMENT IN i TO 2 MHz RANGE
The instrument can accept signals in the band 1
to 2 MHz, applied directly to R. F. IN, with the oscillator
switched off. Input sensitivity is the same as usual.
Ensure the modulation frequency does not take the
frequency beyond the band limits quoted, so as to avoid
introducing distortion caused by the reduced gain outside
the pass band.
Proof that the oscillator is under crystal control
can be obtained by setting the Function switch to SET
FREQ and rocking the tuning control. If the oscillator is
under control the meter reading will not vary.
In general, the tuning control is set to the
required oscillator frequency, but provided the crystal
frequencies do not differ too widely, any of the crystals
can be selected without re-setting the tuning control
between selections.
Operating the instrument in this way cuts out the
frequency inversion caused by the heterodyne system
normally used. The polarity of the DEV + and DEV positions of the Function switch is therefore reversed.
2.10.3 External oscillator
2.12
ASYMMETRIC MODULATION AND CARRIER
SHIFT
If a stable frequency source is available, it may
be preferable to use it rather than the internal oscillator.
Feed the external oscillator signal into the EXT OSC
socket and turn the RANGE-switch to EXT. An input
level of 100 mV into 50 n is required at a frequency 1.5
MHz above the input signal frequency.
The presence of asymmetric modulation usually
indicates distortion in the equipment under test, and is
revealed by unequal meter readings when the Function
switch is turned between PEAK and TROUGH or DEV+
and DEV-.
To make sure that the asymmetry is due to the
input signal, and not introduced by the instrument, retune
the oscillator to the lower peak, 1.5 MHz below the
carrier frequency: If the asymmetry is reversed, i.e., the
original DEV + reading now appears at DEV -, and vice
versa, the asymmetric modulation can be attributed to
the input signal.
The primary use of this facility is for measurement on
r. f. signals which contain harmonics of less than 20 dB
down on the fundamental.
Because the internal
oscillator signal also contains harmonics, mixing two
such signals can give rise to spurious results. A ’pyre’
local oscillator signal prevents this happening.
Secondly, if an external crystal oscillator is available,
it may be preferred to use this, rather than to crystal
control the local oscillator, for low level noise
measurements.
In position SET FREQ, the output from a counter
circuit in the limiter is measured by the meter. When the
meter indicates SET, the i. f. is centered on 1.5 MHz
exactly. If modulation
2-9
TM 11-6625-3017-14
then causes the meter reading to fluctuate, carrier shift is
present. The extent of the shift may be measured by
connecting a counter to I. F. OUT. In cases of severe
carrier shift, the modulation meter must be set up with
modulation on.
2.13
2.15
CRYSTAL SELECTION
Crystal control of the local oscillator reduces
microphony and pick-up from surrounding equipment
where these effects cannot be avoided. At higher
frequencies, distortion due to noise in the oscillator can
be significantly reduced. Up to three crystals can be
plugged into sockets on the oscillator front panel and any
one can be selected by the red coloured section of the
oscillator RANGE switch.
A recommended crystal is a 3rd overtone series
resonant Marconi type Q01670F150/A/S with a specified
frequency between 22 and 44 MHz. Thus, the crystal is
used on its fundamental on Range 3 and appropriate
harmonics on the other and higher ranges. These
crystals are in hermetically sealed, style D miniature
cases conforming to British Standard and U. S. Style
HC6U.
The following simplifies the procedure for establishing the required crystal frequency for any specified
r. f. input between 20.5 and 1600 MHz.
1) Add 1.5 MHz to the r. f. input frequency
2) Divide this sum by the local oscillator harmonic factor
found from Table 2.4 (shown opposite the range
applicable to the r. f. input). This result is the crystal
frequency.
3) Expressing 1) and 2) as a formula:
USE OF L.F. OUTPUT TERMINALS
CAUTION Application of d. c. to these terminals will
cause damage - see section 3.11.
These terminals enable the modulation waveform on the input signal to be monitored or analysed.
They also enable a sensitive external meter to be used to
extend the deviation range down to the level of residual
noise within the instrument.
The terminals are fed by an independent output
stage in the 2nd 1. f. amplifier and therefore the internal
meter is unaffected by loads connected to them.
Depending on the position of the Function
switch, a.m. or f.m. demodulated outputs are obtained.
The output impedance is approximately 600 0 and the
open circuit level approximately 1.5 V for full-scale
deflection on the internal meter. On the 1.5 kHz
deviation range the output level will only be 0.1 mW. On
all other deviation ranges the output level will be 1 mW.
Crystal frequency =
Note : For most purposes, the output can be
terminated with 600 Ω or unterminated. In the latter
case, a voltage due to leakage of C11 may appear at the
output, causing difficulty if a d. c. coupled oscilloscope
is used at high sensitivity.
TABLE 2.4
The 1. f. response is substantially level up to
200 kHz. The output is also available with switched 50
millisec or 75 pisec de-emphasis to restore the
modulation characteristic of signals that have had preemphasis applied.
2.14
(R. F. + 1. 5) MHz
Harmonic factor
USE OF I.F. OUT SOCKET
This socket can be used to measure carrier shift
by connecting a counter to it - see section 2.6 - or to view
the a.m. envelope on an oscilloscope.
It may also be used to measure amplitude
modulation above 50 kHz which normally would not be
passed by the a.m. detector. This is an extended use of
the modulation meter which in practice would probably
be limited by the attenuation of the 10 IQ output
resistance and the input capacitance of the measuring
instrument.
Range
no.
Crystal Selection
R.f input frequency
MHz
1
4
2
9.5 - 20.5
3
4
5
6
7
20.542.5 86.5 174.5
350. 5
1001.5
702.5
1406.5
8
2-10
- 9.5
Local oscillator
harmonic factor
No crystal
control on this
range
42.5
86.5
174.5
350.5
702.5
1406.5
1001.5
1600
No crystal
control on this
range
1
2
4
8
16
32
24
48
TM 11-6625-3017-14
Example : To find the fundamental crystal frequency for
an r. f. input of 83.666 MHz:
Crystals are fully specified in Data Sheet
Q01670F, to which reference should be made
for further details if required. Both data sheet
and crystals are available from The Marconi Co.
Ltd., Chelmsford, Essex.
1) Consulting Table 2. 4, it can be seen that this r. f.
falls within range 4 and the harmonic factor is therefore
2.
83.666+ 1.5
Crystal frequency =
2
= 42. 583 MHz
2.16
F.M. STEREO MEASUREMENTS
Distortion and channel separation in stereo
systems which are designed to meet U. S. Federal
Communications Commission (F. C. C. ) requirements
can be measured with the TF 2300A Modulation Meter.
The general procedures are described in the following
sections.
A +10% tolerance is permitted on the 1.5 MHz i.
f. (+150 kHz) and, since the normal tolerance on
crystal frequency for +20 °C to +60 O C
temperature operation is +0. 01%, a crystal with
a frequency of 42.58 MHz and normal tolerance
should be suitable, and it is not usually necessary
to specify a tighter tolerance.
2.16.1 Harmonic distortion
Note: Where f.m. deviation approaches the full i.
f. bandwidth and the r, f. approaches 1000 MHz ,
the crystal tolerance should be as close as
possible for minimum distortion and crystals with
tighter frequency limits (+6. 003%) should be
specified.
It can be assumed that distortion introduced by
the modulation meter is small in comparison with that in
stereo transmitters, being typically better than 0.1% for
deviations up to ±75 kHz and therefore, for practical
purposes, can be ignored.
The typical frequency spectrum of a G. E. Zenith type of f.m. stereo signal when a 1 kHz test tone
(for example) is applied to the left channel and no signal
to the right, is shown in Fig. 2-5.
In every case the crystal frequency selected
should be such that the lowest possible harmonic factor
gives the required operating frequency.
This is
automatically given by Table 2.4 using the procedure
described.
Ideally, only the fundamental 1 kHz signal in the
left + right (L + R) channel and the 37 and 39 kHz
sidebands of the suppressed sub-carrier in the L - R
channel should be present.
In practice, however,
harmonic distortions will occur at 2, 3, 4 kHz in the L + R
channel and at 37 and 39, 36 and 40, 35 and 41 kHz . in
the L - R channel. These are the distortion components
which it is desired to measure.
Example : Required oscillator frequency is 176 MHz.
1) It can be seen that a crystal of 22 MHz
operating with a harmonic factor of 8 will satisfy
frequency conditions.
2) However, a crystal of 44 MHz operating with a
harmonic factor of 4 should be specified for
maximum output from the oscillator
Fig. 2-5. Frequency spectrum of f.m. stereo signal with 1kHz modulating tone.
2-11
TM 11-662 5-3014-14
The test arrangement for measuring distortion in
an f.m. stereo transmitter is shown for measurements on
the G. E. -Zenith system is given below :-
For practical working purposes, the small
amount of distortion introduced by the modulation meter
can be neglected.
(1)
2.16.2 Channel separation
(2)
(3)
Connect the transmitter output to the modulation meter in accordance with section 2.4 Preparation for Use.
If it were possible to view the 50 Hz to 15 kHz
and the 23 to 53 kHz regions of Fig 2-5 separately, the
waveforms shown in Figs. 2-7 (a) and (b) would be seen.
Set up the modulation meter with the transmitter signal on, in accordance with section 2.5 Measuring F . M. Deviation. The following
notes are intended to amplify the setting
instructions and refer specifically to the G. E. Zenith System.
The ideal composite modulating signal with the
19 kHz pilot tone removed should be the sum of these
waveforms as shown in (c). In practice, there will be
amplitude unbalance and relative phase shift (group
delay error) between the two added signals. These two
effects, which can be viewed on a direct coupled
oscilloscope, are illustrated in (d) and (e), where
amplitude ’B’ represents a signal on the right channel
due to an input on the left channel.
Set the controls as follows :A. M./DEV RANGE: 150 kHz.
MAX MOD FREQ:= 200 kHz.
DE-EMPHASIS : OFF, even if pre-emphasis is
being applied.
Channel 1 separation is given by:
Function: DEV + or DEV -
Separation = 20 log 10 A/B (1)
(4)
Apply a test signal of a chosen frequency to the
left channel with no signal to the right channel.
where A and B are measurements indicated in
Figs. 2-7 (d) and (e).
(5)
Connect Wave Analyser type TF 2330, or an
equivalent instrument for harmonic analysis of
the audio range, to the OUTPUT terminals of the
modulation meter. (Refer to the instruction
manual on the analyser for calibration and
measuring procedures. )
An f.m. stereo transmitter or stereo modulator
must meet specified requirements as regards response
and phase shift. In the F. C. C. requirements, it is
deemed that these are met if the channel separation
exceeds 29.7 dB.
(6)
The frequency spectrum of the demodulated
output of the modulation meter can be obtained
by tuning through the frequency range and
taking measurements at the appropriate
frequencies. The result is usually referred to the
fundamental and expressed as percentages or
dB readings, calculated by the usual method for
harmonic distortion measurement as described
in the wave analyser manual.
A suitable oscilloscope, such as a Marconi
Instruments type TF 2200, connected to the OUTPUT
terminals 6f the modulation meter, enables the channel
separation to be measured. Fig. 2-8 shows typical
oscillograms obtained on a TF 2200 Oscilloscope from
which such measurements would be made.
From 200 Hz to 1 5kHz. the channel separation
figure of the modulation meter is typically 13 dB below
the minimum required of f.m. stereo channels in the F.
C. C. regulations, while at 50 Hz (the worst condition), it
is at least 3 dB below.
Fig. 2-6. Test arrangement for measuring distortion
2-12
TM 11-662 5-3014-14
Fig. 2-7. Derivation of composite
stereo signal showing unbalance and
phase shift errors
The test arrangement for measuring channel
separation is as illustrated in Fig. 2-6, except that the
wave analyser is now replaced by an oscilloscope, and
the procedure is as follows :
(1)
Set up the equipment and modulation meter is
already described for distortion measurements.
Fig. 2-8.(c). With phase shift error
Fig 2-8. Oscillograms of composite signal
2-13
TM 11-6625-3017-14
(2) Apply a test signal to the left channel at 15 kHz
modulation frequency (for example) with no signal on the
right channel.
deviation and divide by the modulating frequency to
obtain the answer in radians
Telemetry deviation
(3)
Connect the oscilloscope, switched to d. c.
coupling, to the OUTPUT terminals of the modulation
meter. If the oscilloscope has a high input resistance it is
advisable to connect a resistor of about 1 kQ (the exact
value is unimportant) in parallel with the oscilloscope
input; this is to prevent leak- age in the electrolytic output
coupling capacitor of the modulation meter from
producing a voltage which may shift the trace off the
screen. Adjust the oscilloscope to suitable time base
and input attenuator settings for a composite signal
waveform as in Fig. 2-8. Procedure here depends on the
equipment being tested, in general it consists of setting
up the system for deviation, and gain etc., in accordance
with individual system manufacturers’ instructions until a
satisfactory waveform is seen. The gain of the L - R
channel should then be adjusted for minimum amplitude
’B’. Measure this amplitude and calculate separation in
accordance with formula (1).
2.17 PHASE
DEVIATION
MODULATION
AND
To measure the deviations in a modulated
telemetry signal connect the OUTPUT terminals to the
external meter via a switched series of band-pass filters
at the sub-carrier frequencies.
This enables the
deviation due to each tone to be measured, having first
calibrated the meter against a signal modulated by a
single tone.
2.18
STRAY FIELDS
The oscillator uses permeability tuning and so
the oscillator frequency may be modulated by stray
magnetic fields. An internal magnetic screen is fitted but
nevertheless we recommend that the oscillator section of
the instrument should not be placed close to other
devices having strong external magnetic fields.
The instrument has internal screening which, for
most purposes, provides adequate attenuation from stray
fields. However, a signal source such as a transmitter of
greater power than about 10 W may cause stray electric
r. f. radiation which may be picked up by the deviation
meter. This means that it may be necessary to take care
in the siting of the instrument. The effect will be most
notice- able when making a.m. measurements; f.m.
measurements will be affected only if the stray field is so
great as to pass the limiters.
TELEMETRY
Phase modulation
To find the degree of phase modulation, measure the
2-14
TM 11-6625-3017-14
Table 2.5.
DECIBEL CONVERSION TABLE
Ratio Down
VOLTAGE
Ratio Up
POWER
DECIBELS
VOLTAGE
POWER
1•0
•9886
•9772
•9661
•9550
•9441
1•0
•9772
•9550
•9333
•9120
•8913
0
•1
•2
•3
•4
•5
1•0
1•012
1023
1•035
1•047
1•059
1•0
1•023
1•047
1•072
1•096
1•122
•9333
•9226
•9120
•9016
•8913
•8710
•8511
•8318
•8128
•7943
•6
•7
•8
•9
1•0
1•072
1•084
1•096
1•109
1•122
1•148
1•175
1•202
1•230
1•259
•8710
•8511
•8318
•8128
•7943
•7586
•7244
•6918
•6607
•6310
1•2
1•4
1•6
1•8
2•0
1•148
1•175
1•202
1•230
1•259
1•318
1•380
1•445
1•514
1•585
•7762
•7586
•7413
•7244
•7079
•6026
•5754
•5495
•5248
•5012
2•2
2•4
2•6
2•8
3•0
1•288
1•318
1•349
1•380
1•413
1•660
1•738
1•820
1•905
1•995
•6683
•6310
•5957
•5623
•5309
•4467
•3981
•3548
•3162
•2818
3•5
4•0
4•5
5•0
5•5
1•496
1•585
1•679
1•778
1•884
2•239
2•512
22818
3•162
3•548
•5012
•4467
•3981
•3548
•3162
•2512
•1995
•1585
•1259
•1000
6
7
8
9
10
1•995
2•239
2•512
2•818
3•162
3•981
5•012
6•310
7•943
10•000
•2818
•2512
•2239
•1995
•1778
•07943
•06310
•05012
•03981
•03162
11
12
13
14
15
3•548
3•981
42467
5•012
5•623
12•59
15•85
19•95
25•12
31•62
2-15
TM 11-6625-3017-14
Table 2-5. DECIBEL CONVERSION TABLE (continued)
Ratio Down
VOLTAGE
Ratio Up
POWER
DECIBELS
VOLTAGE
POWER
•1585
•1413
•1259
•1122
•1000
•02512
•01995
•01585
•01259
•01000
16
17
18
19
20
6•310
7•079
7•943
8•913
10•000
39•81
50•12
63•10
79•43
100•00
•07943
•06310
•05012
•03981
•03162
6•310 x 10
-3
3•981 x 10
-3
2•512 x 10
-3
1•585 x 10
-3
1•000 x 10
-3
22
24
26
28
30
12•59
15•85
19•95
25•12
31•62
158•5
251•2
398•1
631•0
1,000
•02512
•01995
•01585
•01259
•01000
6•310 x 10
-4
3•981 x 10
4
2•512x 10-4
1•585 x 10
-4
1•000 x 10
-4
32
34
36
38
40
39•81
50•12
63•10
79•43
100•00
1•585 x 10
3
2•512 x 10
3
3•981 x 10
3
6•310 x 10
4
1•000 x 10
3
7•943 x 10
-3
6•310 x 10
-3
5•012 x 10
-3
3•981 x 10
-3
3•162 x 10
-3
6•310 x 10
-5
3•981 x 10
-5
2•512 x 10
-5
1•585 x 10
-5
1•000 x 10
-5
42
44
46
48
50
125•9
158•5
199•5
251•2
316•2
1•585 x 10
-4
2•512 x 10
-4
3•981 x 10
-5
6•310 x 10
-5
1•000 x 10
2•512 x 10
-3
1•995 x 10
-3
1•585 x 10
-3
1•259 x 10
-3
1•000 x 10
-3
6•310 x 10
-6
3•981 x 10
-6
2•512 x 10
-6
1•585 x 10
-6
1•000 x 10
-6
52
54
56
58
60
398•1
501•2
631•0
794•3
1,000
1•585 x 10
5
2•512 x 10
5
3•981 x 10
5
6•310 x 10
6
1•000 x 10
-4
3•162 x 10
-7
1•000 x 10
-8
3•162 x 10
-8
1•000 x 10
-9
3•162 x 10
-7
65
70
75
80
85
1•778 x 10
3
3•162 x 10
3
5•623 x 10
4
1•000 x 10
4
1•778 x 10
-5
1•000 x 10
-10
1•000 x 10
-12
1•000 x 10
-12
1•000 x 10
-13
1•000 x 10
-14
1•000 x 10
-9
90
100
110
120
130
140
3•162 x 10-5
1•000 x 10
-5
3•162 x 10
-6
1•000 x 10
6
3•162 x 10-7
1•000 x 10
5•623 x 10
-4
3•162 x 10
-4
1•778 x 10
-4
1•000 X 10
-5
5•623 x 10
3•162 x 10
-5
1•000 x 10
-5
3•162 x 10
6
1•000 x 10-7
3•162 x 10
-7
1•000 x 10
2-16
-4
5
3
4
6
3•162 x 10
7
1•000 x 10
7
3•162 x 10
8
1•000 x 10
8
3•162 x 10
9
1•000 x 10
12
1•000 x 10
11
1•000 x 10
12
1•000 x 10
13
1•000 x 10
14
1•000 x 10
TM 11-6625-3017-14
SECTION 3
TECHNICAL DESCRIPTION
This limited i. f. waveform is passed to the pulse
counter discriminator whose operation is illustrated in (c),
(d) and (e). A pulse of fixed amplitude and width is
generated every time the clipped i. f. signal passes
through zero in the positive-going sense as shown in (b)
and (c). At any given repetition frequency, these pulses
have a constant mean amplitude, Vm, provided the pulse
amplitude and width are fixed; thus when the p. r. f.
varies due to f. m. of the input, the mean amplitude will
also vary directly as the modulation frequency. This is
illustrated in (c) and (d). In practice the limiter output is
fed to a Schmitt trigger circuit, the resultant constant
rise-time rectangular waveform being differentiated and
used to drive a pulse generator. The pulses from here
are later passed through a low-pass filter to remove all
but the modulation frequency components.
3.1 SYSTEM OPERATION
General operation of the TF 2300A Modulation
Meter can be explained with reference to the block
schematic, Fig. 3-1.
The r. f. input is heterodyned in the mixer with the
local oscillator output, producing an intermediate
frequency signal of 1.5 MHz. The output of the mixer is
fed to an i.f. Amplifier which has a linear
phase/frequency response to f. m.
From the i. f. amplifier, the signal can be passed
through the f. m. or the a. m. sections, depending on the
positioning of the Function switch.
The l. f. signal (e) is then amplified in the 1st l. f.
amplifier, the gain of which can be standardized by the
SET CAL-F. M. front panel preset in conjunction with the
calibrator, and passed through the 200 kHz low-pass
filter and, if required, to restrict the bandwidth to the
audio range, through the 15 kHz low-pass filter.
F.M. sections
From the i. f. amplifier, f. m. signals, as illustrated in
Fig. 3-2 (a), are passed through three limiting stages to
eliminate all amplitude changes and produce a
rectangular waveform as shown in (b).
Fig. 3-1. Block schematic diagram.
3-1
TM 11-6625-3017-14
the carrier level at the detector, while in the latter
position, when the i. f. is fixed, it is used to set the mixer
input to the correct level by adjustment of the LEVEL
attenuator and also for oscillator peaking adjustment
during initial setting up of the modulation meter.
A.M./F.M. sections
The A. M. /DEV RANGE attenuator has a total
attenuation of 40 dB. The attenuation in the 1.5 and 5
kHz positions is zero, and in the other deviation positions
increases by 10 dB per step, providing the deviation and
modulation depth ranges on f. m. and a. m. On a. m. only
the 10 and 20 dB steps are used.
5 to 500 kHz deviation ranges:
After attenuation, the signals are passed to the 2nd
1. f. amplifier which contains an output amplifier
arranged to supply approximately 0 dBm into 600 E2 to
the OUTPUT terminals. This stage effectively isolates
the meter circuits from the OUTPUT terminals and
permits de-emphasis networks to be switched in to the
output terminals when required, without affecting the
meter reading. The peak reading meter circuit consists
of an amplifier with push-pull pair to operate the meter
diode in its most linear region.
1.5 kHz deviation ranges:
The signal is passed to the 2nd 1. f.
amplifier which supplies approximately -10 dBm into 600
Ω to the output terminals. Unlike the other deviation
ranges the meter circuits are connected to the output of
the amplifier and thus the de-emphasis networks will
affect the meter reading.
Fig. 3-2. Operation of discriminator
From this point onwards, all sections are common
to f. m. and a. m. and it is necessary to return to the i. f.
amplifier and consider the a. m. sections of the
modulation meter before proceeding to describe these
final sections.
Calibration circuit
A.M. sections
In the SET CAL position of the Function switch, the
calibrator produces a standard crystal controlled
deviation signal, i.e., it produces a similar signal to that
from the limiter, with a peak-to-peak amplitude
corresponding to a ±200 kHz deviation. For a more
complete description of the calibrator, refer to sect. 3. 8.
From the i. f. amplifier, a. m. signals are passed in
the appropriate position of the Function switch to the a.
m. detector. A diode detector is employed, preceded by
an i. f. amplifier stage, the gain of which is variable by the
SET A. M. control to standardize the carrier level at the
detector. When the carrier level is correct, the d. c.
output from the detector produces a reading at the SET
line on the meter.
It thus provides a means of standardizing the
discriminator and 1. f. circuitry in order that accuracy can
be maintained and also a means of checking for all
possible sources of drift.
After detection, the signal is fed via a 50 kHz lowpass filter to the A M. /DEV RANGE switch and other
common a. m. /f. m. sections.
3.2 POWER UNIT (Unit A13--Fig. 7-6)
The d. c. component of the detected a. m. signal is
fed direct to the meter in the SET A. M. and TUNE
OSCILLATOR positions of the Function switch. In the
former position the d. c. component, which is
independent of a. m., is used as already stated to set
Occupying the rear corner behind the oscillator
compartment, the power unit includes two power
transistors fitted to heat sinks on the chassis, a printed
board and electrolytic capac-
3-2
TM 11-6625-3017-14
itors. One switch, SA, on the back panel selects the
mains voltage range, and another, SB, the power source
which may be mains or battery.
where mixing with the local oscillator takes place. The
output from the mixer is at an i. f. of 1.5 MHz.
The normal input range is 4 MHz to 1000 MHz. R.
F. inputs of over 1000 MHz can be used with reduced
sensitivity.
The useful upper limit is governed by
oscillator stability and input sensitivity.
The mains input feeds straight into a low-pass filter,
Z1, to prevent r. f. entering the instrument, then into a
transformer T1, which has a double-wound primary. The
transformer is astatically wound because of the
susceptibility of the oscillator tuning system to magnetic
fields. Its two primary halves are connected in series for
240 V, or parallel for 110 V, according to the. position of
switch SA. The secondary winding, centre tapped to
earth, drives a full-wave rectifier whose output is
smoothed by a conventional R-C network to give about
30 V. A series regulator follows the smoothing circuit,
using integrated circuit regulator U1 to control the output
voltages from series transistor Q1.
3.4 LOCAL OSCILLATOR (Unit A2a-Fig. 7-2)
VT1 produces 5.5 to 11 MHz directly for range 1,
and 11 to 22 MHz second harmonic for range 2. Tuned
by L1, one of the three variable inductors connected to
the main tuning, the oscillator is evolved from the Colpitts
circuit. There is no crystal control on this oscillator. C1
and L2 are provided to pre-adjust the range limits of
frequency to the scale of the oscillator. VT1 is switched
off by the switch SB on ranges 3-4 and 5-8.
The output from this regulator is at -18 V, adjustable
by preset potentiometer RV1, and supplies the a. m.
detector, both amplifiers, the peak reading voltmeter, the
discriminator and the -12 V regulator. Further isolation
from mains voltage variations and hum is required for the
remaining units. This is provided by the -12 V regulator
which uses integrated circuit regulator U2 to control the
output voltage from Q2. Potentiometer R2 sets the -12
volt level. Resistors R6, R7, and R8 sense the load
current to provide short circuit protection.
Ranges 3 and 4 use VT2, tuned by L3, for the
oscillator frequency, which is basically 22 to 44 MHz with
44 to 88 MHz second harmonic. The fundamental
frequency is used for range 3, and the harmonic for
range 4. This oscillator can be controlled by switching
one of three crystals X1, 2, 3 into the circuit of VT2 in
place of the de-coupling capacitor, L3 still needing to be
tuned for maximum output.
Ranges 5 to 8 are derived from the 22 to 44 MHz
oscillator, but the output goes to the multiplier board
before it reaches the mixer.
24 V applied to the BATTERY terminals (positive
earth or isolated) passes through MR3, to avoid risk of
damage through accidental polarity reversal, and goes to
Q1 directly, when SB is in the BATTERY position.
Due to the permeability tuning employed in both
oscillators, outputs cannot be taken from the inductor
coils. The outputs are therefore taken by tapping the
preset tuning capacitors, C1 and C14, by two capacitive
matching systems - C4, 5 or C10, 11 in series. These
outputs are fed via simple fixed attenuators to switch
SB2B except in the case of VT2 on ranges 5-8, when it is
fed via the doubler and harmonic generator board (A2b).
3.3 MIXER (Unit A1--Fig. 7-2)
The mixer is a conventional, untuned, square law
type, using a point contact silicon diode. It is built as a
single, compact screened unit to keep spurious
responses at a low level over the wide frequency range.
Short signal paths are provided to allow operation near
high intensity r. f. fields. The mixer is preceded by the r.
f. attenuator which, at an input impedance of 50 Ω, gives
6 to 60 dB attenuation.
Doubler and harmonic generator (Unit A2b-Fig. 7-2)
VT1 is tuned, rather flatly, by L2 to act as a
frequency doubler to the output from the oscillator VT2
(on A2a). L2 tunes over the range 44 to 88 MHz, and this
signal is applied to the harmonic generator VT2 and VT3
(on A2b), whose output contains all the required
harmonics of the oscillator fundamental.
The r. f. input passes via the continuously variable
attenuator, AT1, into the crystal mixer
3-3
TM 11-6625-3017-14
a d. c. term, Vm, almost proportional to the repetition
frequency. This d. c. is fed, in the SET FREQ positions
of the Function switch, directly to the meter which is
arranged to indicate SET when the i. f. is correct.
3.5 I.F. AMPLIFIER (Unit A3-Fig. 7-2)
This board, in the narrow box alongside the local
oscillator and power unit, contains three amplifying
stages, each of two transistors, Q1 to Q6, the stages
being coupled via band pass filters. No limiting occurs in
the amplifier, and linearity, frequency response and an
overall gain of 50 dB are stabilized by a negative
feedback loop in each stage.
The presence of any appreciable degree of carrier
shift when modulation is applied to the input signal will be
indicated by the meter in the SET FREQ positions; the
amount of shift may be measured with a counter at I. F.
OUT provided that the gate time is long with respect to
the period of the modulating signal or is equal to an
integral number of periods.
The output of the i. f. amplifier is taken in parallel
paths to the Function switch, SB, and to the I. F. OUT
socket via resistor R1 where it is available for viewing on
an oscilloscope or for counting to check carrier frequency
drift. Via SB1 F, the output is routed to the a. m.
Detector or, in the f. m. positions, to the limiter.
3.7 DISCRIMINATOR (Unit A5-Fig. 7-3)
The pulse counter type discriminator occupies the
front half of the central compartment fitted beneath the
chassis, the rear half of this compartment being
occupied by the limiter. The overall operation of the
discriminator is described in section 3.1 and illustrated in
Fig. 3-2 (c), (d)’ and (e).
3.6 LIMITER (Unit A4 Fig. 7-3)
Housed in the rear half of a compartment
underneath the centre of the chassis, the limiter consists
of three stages of emitter-coupled amplifiers, arranged
so that signal amplitudes of either polarity above a
certain level are limited. The emitters are connected to
balancing potentiometers to equalize the excursion in
each direction.
The limiter output drives a Schmitt trigger circuit, Q2
and Q3, to produce a large square wave output into C4
with constant rise and fall times. The collector voltage
of QI, the trigger amplifier, is set by RV1 so that the
Schmitt circuit is on the point of regeneration.
The square wave is differentiated and passed to a
pulse generator, Q4 and Q5, which produces positivegoing pulses. These pulses are clipped b3 Q6. The
emitter of this semiconductor is taken to the -12 V line,
so that it clips the bases of the positive-going pulses,
thus maintaining constant amplitude.
Part of the i. f. signal is tapped off from the third
stage, differentiated by C7 and LI and detected by MIl1 to
produce the uni-directional pulses shown in Fig. 3-3
(c).These pulses have
Q7 is an emitter follower which, unlike Q6, is
conducting continuously and presents a constant low
impedance to the 200 kHz low-pass filter. The low
frequency change in the mean value of the pulses is
therefore passed and the i. f. signal rejected.
3.8 CALIBRATOR (Unit A12-Fig. 7-5)
Q1 and Q2 form a multivibrator running at nominally
4 kHz. CG, R8 and Q4 differentiate and clip the negative
spikes of the square wave output from Q2 and feed them
from a low impedance to the binary divider, Q7 and Q8.
Fig. 3-3. Operation of limiter
3-4
TM 11-6625-3017-14
Since the multivibrator runs at constant frequency,
the positive-going pulses from Q4 are at equal time
intervals. Q7 and Q8 divide these 4 kHz pulses by two
and produce an exactly 1:1 square wave output, via C11,
at about 2 kHz. Q5 and Q6 operate as a gating circuit
controlled at 2 kHz by this square wave.
200 kHz and 15 kHz
These filters are 3 dB down at 250 and 28 kHz
respectively to obtain optimum flatness over their pass
ands of 200 and 15 kHz. In order to accommodate the
channel separation requirements of stereo broadcast
monitoring, the filter designs are such as to provide a
linear phase frequency response.
Q3 is an oscillator accurately controlled at 400 kHz
by crystal XLI and gated on and off by Q5 and Q6 at 2
kHz. Thus the 400 kHz signal is divided into bursts of r.f.
at a repetition frequency of 2 kHz and a 1:1 on/off ratio see Fig. 3-4. This is fed to the discriminator via C9 when
SB is at position SET CAL and corresponds, for
calibration purposes, to a crystal controlled deviation of
±200 kHz. It should be noted that, in this mode, the 15
kHz filter is always in circuit to reduce the tendency of
high frequency ringing due to the use of a square wave
for calibration.
The 200 kHz filter integrates the pulses from the
discriminator and rejects the i. f. signal; thus it produces
a low frequency voltage which is proportional in
amplitude to the deviation. The 15 kHz filter restricts the
bandwidth to the audio range and can be switched in as
required by switch SE.
3.10 1st L.F. AMPLIFIER (Unit A7 Fig. 7-3)
Demodulated signals from the discriminator reach
the first 1. f. amplifier via the 200 kHz low-pass filter. The
amplifier has three stages, Q1 and 2 being a current
feedback pair, while Q3 and 4 are arranged as a special
low impedance configuration known as an ’emittersquared follower.
The amplifier has been designed to give high
stability, large bandwidth and constant gain with
immunity from h. t. changes, by virtue of its feedback
loops. C6 carries positive feedback over part df the
circuit to increase the gain, while R8 carries d. c. bias to
the first stage. C5 and R7 take a. c. negative feedback to
the first stage via the SET CAL F. M. control. The output
stage, Q3 and Q4, gives a very low impedance, so that
the output impedance of the amplifier is due almost
entirely to R14. A high stability resistor is used here to
give optimum matching to the following switched 15 kHz
filter. Similar considerations apply to the input stage,
where the impedance is effectively lowered by parallel
negative feedback, and R2 matches the preceding unit,
the 200 kHz low-pass filter
Fig. 3-4. Derivation of standard
deviation signal from
400 kHz oscillator
The calibrator operates only in the SET CAL
position of the Function switch, being switched off at all
other positions. A single attenuator pad contains the
variable resistor AORV3 (see Fig. 7-1). This resistor
(fitted immediately behind the calibrator board on the
chassis) can be used to standardize the meter deflection
to the SET mark.
CAUTION
Range attenuator (Chassis A0-Fig. 7-1)
Between the first and second 1. f. Amplifiers is the
range attenuator. The 1.5 and 5 kHz ranges are directly
connected, but for each succeeding range 10 dB
attenuation is switched into circuit. Two meter scales are
used alternately to give 10 dB steps.
Do not attempt to SET CAL on the 1.5 kHz
f. m. deviation range.
3.11 2nd L.F. AMPLIFIER (Unit A9-- Fig. 7-4)
3.9 LOW-PASS FILTERS (Units A6 and A8-Fig. 7-3)
The action of Q1 and Q2 in this unit is similar to that
of the first two transistors in the first 1. f. amplifier. RV1
in the feedback loop sets the gain. Two connections are
made after
3-5
TM 11-6625-3017-14
Q2; one via a switch, so that on the 5 to 500kHz
deviation ranges the meter circuit is connected to
terminal 7, and the other from terminal 9 to the DEEMPHASIS switch. On the 1.5 kHz deviation range the
meter circuit is connected to the output of the amplifier
by terminal 11.
output impedance of Q3. This gives the circuit a wide
band response which is flat to within the limits of the i. f.
amplifier. MR1 feeds into a resistive load and a fraction
of the voltage developed across the load is tapped off
and fed to a 50 kHz low-pass filter.
When the Function switch, SB, is in positions
TROUGH or PEAK, the detected signal is fed via
terminal 12 to the range switch, the 2nd i. f. amplifier and
the meter circuit.
The remainder of the amplifier is the same as the
first 1. f. amplifier and its output is taken to the front
panel terminals. Headphones may be used here, or a
distortion factor meter, external meter (or oscilloscope).
The output impedance is 600 Q1, and is isolated by C11.
Do not allow d. c. to reach the OUTPUT terminals so as
to avoid damaging C11, which is a low voltage
electrolytic capacitor.
When making an a. m. measurement, the internal
meter is switched directly to terminal 7 by the Function
switch, SB, and the d. c. component adjusted by RV1,
SET AM control, until the meter reads SET.
The d. c. component is also used for setting the
input level to the i. f. amplifier, thus ensuring correct
loading and good signal-to-noise ratio. On position
TUNE OSCILLATOR AND ADJUST LEVEL of the
Function switch, a fixed resistor, R1, is switched in place
of RV1 and the correct level set up by adjusting the input
attenuator until the meter indicates within the black arc.
3.12 PEAK READING METER (Unit A10-Fig. 7-4)
For reading modulation depth and deviation, and for
setting the f. m. calibration, the peak reading meter
circuit is brought into use.
Q1 and Q2 amplify the signal from the 2nd 1. f.
amplifier and RV1 presets the gain of the amplifier. The
remainder of the circuit consists of two similar pairs of
semiconductors arranged in push-pull, driving the meter
via rectifier MR1. The polarity of the meter can be
switched to read trough or peak on a. m., the positive or
negative deviation on f. m. Feedback is used to stabilize
the gain, reduce distortion and broaden the fre-quency
response. The feedback loops include R3, R12, C14,
R16, R19 and R24.
3.14 BETWEEN-UNITS CIRCUITRY (Unit A0-Fig. 7-1)
The A. M./DEV RANGE switch, SC, controls three
Tr pads of 10, 20 and 20 dB respectively. These
attenuating pads are inserted in steps as follows:
(1)
(2)
(3)
(4)
(5)
(6)
The meter is also used to measure the d. c.
component of the output from the a. m. detector for i. f.
level monitoring and tuning, and in the position SET
FREQ it reads the voltage developed by a counter circuit
in the limiter thus monitoring the frequency from the
mixer for fine tuning purposes.
Range
1.5kHz f. m.
5 kHz f. m.
15 kHz f. m., 30% a. m.
50 kHz f. m. , 100% a. m.
150 kHz f. m.
500 kHz f. m.
Attenuation
0
0
10 dB
20 dB
10 dB +20 dB
20 dB + 20 dB
3.13 A.M. detector (Unit All-Fig. 7-5)
If should be noted that the meter has two deviation
scales; ranges 2, 4, 6 are associated with the bottom
scale and the other ranges with the upper.
The diode detector, MR1, is preceded by Q2 and
Q3 which are arranged in a composite emitter follower
configuration to give a large peak-to-peak signal without
distortion, and thus allowing MR1 to operate over the
linear part of its forward characteristic. The input to the
detector is via a common-emitter amplifier, Q1, stabilized
by negative feedback through R6 and R7.
Also on the chassis is a single attenuator pad for
the calibrator. This is switched in place of the range
attenuator on the SET CAL position of the Function
switch. This pad incorporates a variable resistor, RV3,
which is mounted on the top of the chassis immediately
to the rear of the calibrator board. RV3 standardizes the
calibration circuit to the meter.
MR1 is fed directly from a tuned circuit, C4 and L1,
which is heavily damped by the low
3-6
TM 11-6625-3017-14
SECTION 4
MAINTENANCE
units above and below the chassis. Components may be
identified by markings on the boards and chassis. For
replacement of sub-assemblies and components, see
Sects. 5. 5 and 5. 6.
4.1 INTRODUCTION
This section contains information for keeping the
equipment in good working order and for checking its
overall performance.
4.3 PERFORMANCE CHECKS
The tests in this section may be used as a routine
maintenance procedure to verify the main performance
parameters of the instrument.
All tests can be
completed without removing the case, except where
some internal readjustment is indicated. Tests may be
done at any convenient frequency within the carrier
range of the modulation meter provided that this
frequency is also within the range of the test equipment
items a, b, c, d and g.
CAUTION This instrument uses semiconductor
devices which, although having inherent long term
reliability and mechanical ruggedness, are susceptible to
damage by overloading, reversed polarity and excessive
heat or radiation. Avoid hazards such as reversal of
batteries, prolonged soldering, strong r. f. fields or other
forms of radiation, use of insulation testers or
accidentally applied short circuits. Even the leakage
current from an unearthed soldering iron could cause
trouble. Before shorting or breaking any circuit, refer to
the circuit diagrams to establish the effect on bias
arrangements of the transistors.
4.3.1
Test equipment required
See Table 4. 1.
Screw fasteners
4.3.2
Screw threads used on this instrument are of the
following sizes - 8BA, 6BA, 4BA, 2BA and 1/4 BSF.
R.F. input and i.f. output
Test equipment:- a, d, e and 1.
Cruciform headed screws are of the Phillips
Pozidriv pattern; to avoid damaging them a Pozidriv
screwdriver should be used.
This procedure verifies the sensitivity of the
modulation meter and the adjustment of the local
oscillator.
4.2 ACCESS AND LAYOUT
R.F. input resistance
The main case assembly is held in position by the
rear panel. This panel may be removed after unscrewing
the four coin-slotted screws across the corners; the
mains lead is held to the rear panel by a clip and will
come away with it if the mains plug is withdrawn. The
instrument can now be slid forward, out of the case;
alternatively, it can be placed face-downwards on a soft
surface and the case lifted off.
(1)
Turn the LEVEL control mid-way. Connect the
multimeter, set for resistance measurement,
between the centre pin of the R. F. IN socket and
earth and check that the reading is 50 Ω ±10 Ω
R.F. sensitivity
Rack-mounted models have top and bottom dust
covers, each attached by four screws.
(2)
Figs. 4-1 and 4-2 show the general location of all
4-1
Adjust the signal generator to give a c. w. output of
about 50 mV and connect it to the R. F. INPUT
socket of the modulation meter and to the
voltmeter, keeping the leads as short as possible.
TM 11-6625-3017-14
Fig. 4-1. units and parts location (top)
4-2
TM 11-6625-3017-14
Fig. 4-2. Units and parts location (bottom)
4-3
TM 11-6625-3017-14
Table 4.1. Test Equipment Required.
Item
(3)
(4)
Type
Minimum specification
a
A. M. signal
generator
Output: 100 mV across 50 Q
A. M.: 80%
Envelope distortion: 1% at 50% mod.
TF 2002B
b
F. M. signal
generator
Deviation: 4 to 250 kHz
Mod. freq.: 0 to 200 kHz
Spurious a. m.: 1%
TF 2008
c
F. M. signal
generator
Output: 200 mV across 50 n
Deviation: 4 to 250 kHz
Mod. freq.: 0 to 200 kHz
TF 1066B/6
(Mod. freq.: 40 Hz 100 kHz)
d
Electronic
voltmeter
Sensitivity: 10 mV
r. m. s. or average reading
dB calibration
Hewlett-Packard
HP 3406
e
Frequency
meter
Frequency: 20 kHz to 1.5 MHz
Sensitivity: 10 mV
Hewlett-Packard HP 5245L
with HP 5261A
f
L. F. oscillator
Frequency: 800 Hz to 56 kHz
Distortion: 0.5%
Hewlett-Packard
HP 209A
g
Spectrum
Resolution: 60 dB at 50 Hz
TF 2370
h
Oscilloscope
L. F. general purpose
Hewlett-Packard HP 1700B
i
Selective
level meter
Frequency: 1.4 to 1.6 MHz
Siemens
Pegelmesser
j
Crystal
oscillator
k
Low-pass
filter
l
Multimeter
40 to 60 Ω
To measure resistance,
HP410A
Hewlett-Packard
m
Amplitude
modulator
A. M. depth: 80%
TM 9897A
Any available frequency with range of
10 to 500 MHz, with output between
20 and 100 mV.
Cut-off frequency: 15 kHz
On the modulation meter, turn the oscillator RANGE
switch and TUNE control to suit the r. f. input
frequency, the Function switch to TUNE
OSCILLATOR AND ADJUST LEVEL and the
LEVEL control fully clockwise.
Recommended model
See Sect. 2.9
meter deflection is at the bottom of the black arc.
(5)
Tune for peak meter deflection and then adjust the
signal generator output until the
4-4
Check that the signal generator output, as indicated
on the voltmeter, is within the figure given for r. f.
input sensitivity in Sect. 1.2 - Data Summary. If not,
check the harmonic generator alignment as in
Sect. 5.4.5 and/or the output of the oscillator.
TM 11-6625-3017-14
(1) Connect the signal generator, externally modulated
by the l. f. oscillator, to the inputs of the modulation
meter and the spectrum analyser, as shown in Fig. 4-3.
I.F. output and frequency
(6)
Connect the frequency meter and voltmeter to the
I.F.
OUT socket and check that the i.f. is
approx.200 mV (with the meter reading at the
bottom ofthe black arc) and remains within 10% of
1.5 MHz when the modulation depth of the input
signal is varied from 0 to 80%o. (Keep the leads as
short at possible.) If the frequency is in error see
Sect. 5.4.10.
NOTE
: Follow steps (4), (5), and (6) of section 2.5
to set the Function switch to F.M. SET
FREQ. and tune the oscillator frequency to
position the meter pointer to the SET line.
Fig. 4-3. Bessel zero measurement
I.F. output impedance
(7)
(2)
Adjust the oscillator frequency, checked against the
frequency meter, to 26.27 kHz. Slowly increase the
signal generator deviation from zero until the carrier
component, viewed on the spectrum analyser,
disappears for the second time. This occurs at a
deviation ratio of 5.52, which means that the
deviation is 145 kHz.
(The MAX MOD
FREQUENCY should be 200 kHz.)
(3)
Set up the modulation meter to measure this signal
as described in Sect. 2.5, using the 150 kHz DEV
RANGE.
(4)
If the modulation meter reading differs from 145
kHz when switched to either DEV+ or DEV-, adjust
the SET CAL F. M. preset to give the best
compromise
accuracy
between
the
two
measurements. Then turn the
Adjust the LEVEL control to increase the voltage at
the I.F. OUT socket to 700 mV. Connect a 10 k Ω ±
2% resistor across the voltmeter input and check
that reading drops to between 310 and 400 mV.
4.3.3 F.M. deviation accuracy
Test equipment:- b, d, e and g.
The internal f. m. calibrator provides a standard of
good long-term stability for checking and resetting the
deviation reading accuracy as described in Section 2.5
(8). The calibrator accuracy is largely dependent on the
frequency of its 200 kHz oscillator crystal, which is
unlikely to change significantly. If the calibrator accuracy
is suspected, the deviation reading should be checked by
making a normal measurement on a symmetrically
modulated signal of accurately known deviation set up by
the Bessel Zero method described below.
DEV RANGE
kHz
500
150
50
5
1.5
MAX MOD
FREQ range
kHz
200
200
200
200
15
15
15
15
15
15
15
TABLE 4.2
F.M. Deviation Accuracy
Deviation
Modulating
kHz
frequency
kHz
480
360.7
145
145
48
48
14.5
14.5
4.8
4.8
1.4
55.46
150
26.27
26.27
8.696
8.696
2.627
2.627
0.8696
0.8696
0.5822
4-5
Carrier
disappearance
3
1
2
2
2
2
2
2
2
2
1
TM 11-6625-3017-14
Function switch to SET CAL and, without disturbing the
SET CAL F. M. preset, bring the meter reading to the
SET mark by adjust-ing the internal f. m. preset, AORV3
- see Fig. 4-1. If this has insufficient range select a new
value for resistor AOR15.
(5)
This check can also be made at other deviations as
shown in Table 4.2.
(6)
If the deviation errors show a general trend in one
direction the presets RV1, RV3, RV5 and RV4
should be adjusted to give the best compromise on
their respective ranges. As RV3 affects all ranges it
should be adjusted first.
Preset
Adjust for best compromise
on deviation range
(kHz)
RV3
RV4
RV5
RV1 (on TM8742)
(3)
Connect the selective level meter to the I. F. OUT
socket of the modulation meter, tune the level
meter to the carrier frequency of 1.5 MHz and set
its gain to give a 0 dB reference level.
(4)
Retune the level meter to one of the 3 kHz
sidebands and adjust the l. f. oscillator out-put to
give a level meter reading of 12 dB below the
reference level. If the sideband levels are different,
adjust for a mean reading of 12 dB. This
corresponds to a modulation depth of 50%.
(5)
If the modulation meter reading differs from 50%
when switched to either PEAK or TROUGH, adjust
the internal preset A9RV1 for the best compromise
accuracy between the two readings.
Note: Adjustment of RV1 may affect the accuracy of the
f. m. deviation reading; therefore, after adjusting
RV1, reset the f. m. calibration as shown in Sect. 2.5
(8) (not by adjusting the internal preset).
5, 15, 50
500
150
1.5
(6)
This check can also be. made. at other modulation
depths, as shown in the following table, in order to
optimize reading errors.
(RV3 will be usually found to give the best compromise
by adjusting on the 5 kHz deviation range.)
4.3.4
A.M. RANGE
%
A.M. depth accuracy
100
100
100
100
100
100
30
30
30
Test equipment:- a, f and i.
A. M. depth accuracy, unlike f.m. deviation, cannot
be checked against an internal calibrating circuit.
Therefore, the a. m. Measurement accuracy can only be
checked by making a normal measurement on a signal
of accurately known modulation depth. A depth of about
50% is recommended. It is important that this signal
should have a very low envelope distortion as this can
cause an apparent error in depth indication.
90
80
70
60
50
40
30
20
10
Sideband
amplitude, dB
-6.94
-7.96
-9.12
-10.46
-12.04
-14.02
-16.52
-20.00
-26.02
The higher modulation depths are not recommended
unless an unusually low envelope distortion can be
achieved.
The modulation depth can be checked by means of
a selective level meter as follows:(1)
TABLE 4.3
Modulation Depth
Modulation
Set the 1. f. oscillator frequency to 3 kHz and use it
to modulate the signal generator to a depth of
nominally 50%.
4.3.5
F.M noise
Test equipment:- b, d, h, j and k.
(2)
Set up the modulation meter for measuring this
signal as described in Sect. 2.6.
This is measured by comparing the output of the
modulation meter when 5 kHz deviation is applied with
the output when deviation is zero.
4-6
TM 11-6625-3017-14
Fig. 4-4. F.M. noise
measurement
To ensure that the latter output is due to the modulation
meter alone it is important that the source should be
exceptionally free from spurious noise deviation.
(1)
Apply an f.m. input with 5 kHz deviation from the
signal generator. Connect the oscilloscope, filter
and voltmeter to the OUTPUT terminals as shown
in Fig. 4-4.
(2)
Set
the
modulation
meter
for
deviation
measurement as in Sect. 2.5, with the local
oscillator crystal-controlled (see Sect. 2.15). Switch
the DEV RANGE to 5 kc/s and the MAX MOD
FREQ to 15 kHz.
(3)
Note the reading on the voltmeter - this should be
about 0 dBm if the modulation meter is terminated
in 600 n.
(2)
On the modulation meter set the Function switch to
TUNE and the oscillator RANGE switch to EXT.
Adjust the frequency of c for maximum reading on
the TF 2300A meter and adjust the TF 2300A
LEVEL control for a reading within the black arc.
Fig. 4-5. F.M. distortion measurement
(4)
(5)
Replace the signal generator with the external
crystal oscillator set to the same output level and
note the reduction in volt-meter reading. This
should be at least 50 dB, which is equivalent to a
noise level of -70 dB with reference to 50 kHz
deviation in a 15 kHz bandwidth.
(3)
Switch to F. M. SET FREQ and adjust c frequency
to bring the TF 2300A meter reading to the SET
mark.
(4)
Switch to DEV+ and turn the MAX MOD FREQ
switch to 15 kHz and the DEV RANGE switch to
150 kHz.
Apply external modulation to the two signal generators
as follows:
Note that the oscilloscope trace is free from hum,
external field and noise. If not, check the power
supply ripple - see Sect. 5.4.3.
Sig. gen.
4.3.6
F.M. distortion
Test equipment:- b, c, 2f and i.
(1)
Set up the equipment as shown in Fig. 4-5. Adjust
c to give a c. w. output of 200 mV at any convenient
frequency Fc1. Adjust b to give a c. w. output of 50
mV at frequency (Fc1- 1.5 MHz).
TABLE 4.4
External Modulation
Mod. freq.
Deviation
c
16 kHz (fl)
37.5 kHz
b
14 kHz (f2)
37.5 kHz
Switch off b and set up the level meter to give a
reference level of -6 dB at 150 kHz. Switch on b again.
Measure the levels of the following components: 4-7
TM 11-6625-3017-14
2nd harmonic: (fl -f2):
2 kHz
3rd harmonic: (2f2 -fl):
12 kHz
and express them in dB’s relative to 0 dB. Add +6 dB to
the 2nd harmonic reading and +9 dB to the 3rd harmonic
reading. The r. m. s. sum of the two levels (see below
for method of calculation) should be lower than -54 dB
(0. 2%. Distortion limits for other values of deviation and
modulation frequency are given in Sect. 1.2 - Data
Summary.
Fig. 4-7. A.M. rejection measurement
(3) Switch to F. M. - SET FREQ and adjust the
OSCILLATOR tune control to bring the meter reading to
the SET mark.
Summation of dB levels
The r. m. s. sum of two dB levels can be obtained
by increasing the level of the larger one by an increment
between 0 and 3 dB; the value of increment depends on
the difference between the two levels as shown by the
graph. For example, if the two levels are -40 dB and -46
dB, giving a difference of 6 dB, the increment is 1 dB; the
sum of the two levels is therefore -40 +1 dB = -39 dB.
(4)
Switch to TUNE and adjust the LEVEL control to
give a reading just below full-scale on the
black arc.
(5)
Turn the DEV RANGE switch to 5 kHz and the MAX
MOD FREQ switch to 15 kHz.
(6)
Switch to DEV+ and DEV- in turn and check that
the residual reading on the meter is less than about
150 Hz.
Fig. 4-6. Summation of dB levels
4.4 CLEANING AND LUBRICATING
Rotary switch contacts
These should be cleaned once or twice a year,
depending on usage, with benzine or white spirit (not
carbon tetrachloride). After cleaning wipe the contacts
with a suitable lubricant such as a 1% solution of
petroleum jelly in white spirit.
4.3.7
A.M. rejection
Oscillator unit
Test equipment:- a, f and m.
Excessive lubrication must be avoided but the
moving parts should be cleaned and lubricated at least
twice a year:
(1) Set up the equipment as shown in Fig. 4-7. Adjust
the signal generator to give a c. w. output of 100 mV at
any convenient frequency. Adjust the I. f. oscillator
frequency to 1 kHz at a level which gives 80%
modulation as measured on the TF 2300A.
(2) On the TF 2300A set the Function switch to TUNE
and the OSCILLATOR TUNE control to give maximum
meter reading. Then adjust the LEVEL control for a
reading within the black arc.
(a)
Worm shaft: Use Rocol anti-scuffing paste.
(b)
Carriage slide: Use Aeroshell 4 oil.
(c)
Scale drum mounting: Apply a few drops of
Aeroshell 4 oil to the felt washer on the spigot
mounting.
(d)
Range switch bevel gears: Use Rocol antiscuffing paste.
Note:
4-8
Sealed bearings at end of worm shaft will not
require lubrication within the life of the instrument.
TM 11-6625-3017-14
Fig. 4-8. Oscillator lubrication points
4-9
TM 11-6625-3017-14
SECTION 5
REPAIR
(iii) Systematic calibration, which can be used to locate
a fault for which methods (i) and (ii) are inadequate
- see Sect. 5.4.
5.1 INTRODUCTION
This chapter contains information for the
localization and repair of faults. Performance limits
quoted are for guidance only and should not be taken as
guaranteed performance specifications unless they are
also quoted in the Data Summary section.
5.2.1
Test equipment required
See Table 5.1.
CAUTION
See Maintenance, Sect. 4.1, for
precautions in handling semiconductors and for
advice on screw fasteners.
5.2.2
In the case of any difficulty, please write to or phone
the Marconi Instruments Service Division (see address
on back cover) or nearest representative, quoting the
type and serial number on the data plate at the rear of
the instrument. If the instrument is being returned for
repair, please indicate clearly the nature of the fault or
the work you require to be done.
As a first step in fault finding, the three following
tests will help you to verify nearly all the circuits of the
modulation meter and to localize the fault to certain
areas. These tests can be performed without removing
the cover. Failure of all three tests may indicate a faulty
power supply, in which case first check the fuses on the
rear panel.
(1)
Turn the Function switch to SET CAL. If the meter
reads SET, the calibrator (A12) and the
discriminator, 1st and 2nd 1. f. amplifier, peak
reading voltmeter and associated circuits (A5 to
A10) are working. If there is no meter indication,
but the 2 kHz calibrator square wave can be seen
with an oscilloscope at the OUTPUT terminals, then
the peak reading voltmeter circuit, (A10), is faulty.
(2)
Turn the Function switch to TUNE OSCILLATOR
AND ADJUST LEVEL. Connect a signal to the R.
F. IN socket and check that, by adjusting the
TABLE 5.1
5.2 FAULT LOCATION
General procedure
Methodical fault location can be performed at the
following three levels:
(i)
(ii)
Front panel functional checks for
localization of a fault - see Sect. 5.2.2..
Front panel checks
general
Internal checks for more detailed localization -see
Sect. 5.2.3 and figures 4.1, 4.2, and 5.5 through 517.
Table 5.1
Test Equipment Required for Fault Location
Minimum specification
Item
Type
a
Signal
generator
Frequency: .1.5 MHz and between
4 and 1000 MHz
Output: c. w., up to 100 mV.
TF 995B2,
TF 2006
b
Multimeter
250 V a.c.
20 V d. c. at 20 kS/V
Hewlett-Packard
HP410A
c
Measuring
Bandwidth:5 MHz
oscilloscope Sensitivity: 20 mV/cm
5-1
Recommended model
Hewlett-Packard
HP 1700B
TM 11-6625-3017-14
OSCILLATOR TUNE and LEVEL controls, a meter
deflection in the black arc can be obtained. If so,
the local oscillator, mixer and i. f. amplifier (Al to
A3), most of the a. m. detector (All) and the peak
reading voltmeter (A10) are working.
(2)
If not, but the meter deflects when the input
frequency is changed to the i. f. of 1.5 MHz, then
the-local oscillator or mixer are suspect. A fault in
the local oscillator can be confirmed if the first
paragraph of test 2 gives a positive result when
using an external local oscillator.
(3)
Having identified a faulty board, use the static
voltage information on the circuit diagrams as a
guide to locating the source of the trouble.
Turn the Function switch to F. M. SET FREQ. or
A.M. SET FREQ. (after setting up the meter
deflection as in step 2 above). Check that the
meter deflects to the SET mark when the
OSCILLATOR TUNE control is slightly readjusted.
If so, the limiter circuit (A4) is working.
5.3 WAVEFORMS
The oscillograms illustrated in Fig. 6-1 show the
significant waveforms that occur between the output of
the calibrator unit (A12) and the OUT-PUT terminals.
The measuring points are indicated on the inter-unit
wiring diagram, FO 6-1, and the circuit diagrams.
Input attenuator
Measurement should be made with an oscilloscope
of at least 5 MHz bandwidth and 20 mV/cm sensitivity,
such as M.I. type TF 2201 series. Contact with the
printed board edge connectors may be made from below
the chassis but, if more convenient, the Extension Board
TM 7926 may be used to allow access from above the
chassis.
This can be checked by feeding a 1.5 MHz signal
into the EXT OSC socket when the sensitivity should be
approximately 20 mV input for a meter reading on the
bottom of the black arc when the function switch is set to
TUNE. If a 5 mV signal is now applied to the R. F.
INPUT socket a meter reading will be produced again on
the black arc. If there is no deflection when the 29 mV
signal is applied to the EXT OSC socket the attenuator
or part of the mixer is faulty. It is more likely to be the
attenuator.
5.2.3
5.4 REALIGNMENT
5.4.1
Introduction
This is a complete realignment procedure with the
steps arranged in a logical order. If the full procedure is
not required, for example following a component
replacement, individual steps may be performed
providing they do not interact with other adjustments.
Although the likelihood of such interaction is pointed out
wherever possible, it is recommended that you always
consider the effects of any readjustment by reference to
the circuit diagrams.
Internal checks
Having roughly localized the fault by the front-panel
tests it may be more accurately located by signal tracing
tests, using the inter-unit wiring diagram as a guide.
(1)
If trouble is suspected between the calibrator unit
and the meter, turn the Function switch to SET CAL
and check the calibrator wave-forms from the
calibrator unit output to the meter. These should be
as shown in Sect. 5.3, although the frequency of.
the square wave modulation is not critical and may
differ from the nominal 2 kHz value illustrated
First check the power supply unit output voltages at
A13C9 (-18 V) and C12 (-12 V) - see Fig. 4-2 for
location. If incorrect, reset as described in Sect.
5.4. 3. If the fuses are intact and there is no output
from the power supply unit when a. c, operated, try
changing to battery operation. If this restores the
output, a faulty transformer/- rectifier circuit is
indicated.
NOTE: Performance limits given in this section are for
guidance only and should not be taken as guaranteed
performance specifications unless they are also quoted
in the Data Summary section.
5.4.2
5-2
Test equipment required - see Table 5.2.
TM 11-6625-3017-14
Fig. 5-1. Oscillograms
The conditions to obtain these waveforms are as follows:
DE-EMPHASIS switch to OFF. Function switch to SET CAL.
5-3
TM 11-6625-3017-14
TABLE 5.2
Test Equipment Required for Realignment
Item
Type
Minimum specification
Recommended model
a
Multimeter
Range: 0 - 20 V d. c.
0 - 270 V a. c.
Hewlett-Packard
HP410A
b
Variable mains
transformer
Range: 190 - 260 or
90 - 160 V a. c.
General Radio
Model W1OMT3A
c
Wave analyser
Range: 50 - 200 Hz
Sensitivity: 50 µV
Hewlett-Packard
HP 302A
d
Differential
voltmeter
Discrimination: 1 mV in 18 V
Fluke
Model 881AB
e
Frequency meter
Range: f*
Hewlett-Packard HP 5245L
with HP 5261A
f
R. F.
millivoltmeter
Range: f*
HP 3406
Hewlett-Packard
g
T connector
BNC-BNC-BNC
h
Crystals
Frequencies: 22, 23 and 44 MHz
i
Response
analyser
4 to 1000 MHz
Rhode & Schwarz
’Polyskop’ SWOB II
j
Signal source
Range: 100 Hz - 23 kHz
TF 2001 with
standardized attenuator
k
Sensitive
voltmeter
Range: 100 Hz - 23 kHz with
dB calibration
Hewlett-Packard
HP 427A
l
Crystal oscillator
Frequency: 1.5 MHz
m
Capacitor
0.014 µ LF
n
R. M. S. voltmeter
Frequency: 30 Hz - 150 kHz
Sensitivity: 1 mV full-scale
Hewlett-Packard
HP 3400A
o
Oscilloscope
Sensitivity: 10 mV/cm
Hewlett-Packard
HP 1700B
f*;
range to suit user’s requirements within coverage of TF 2300
(4 to 1000 MHz).
5-4
TM 11-6625-3017-14
-12 V line should be not more than +2 mV,
and preferably about +1 mV.
5.4.3 Power supply
Test equipment:- a, b, c and d
(1)
5.4.4
Measure the output of the -18 V and -12 V
regulated supplies at the points illustrated in
Fig. 5-2..
Test equipment:- e, f, g' and h
(1)
Connect the frequency meter and millivolt-meter via
a T-connector to the output plug of the oscillator,
PLB. Turn the LEVEL control fully clockwise.
(2)
Switch to oscillator RANGE 1-2, tune through the
range and check that the dial calibration is within
±3% of the frequency meter reading and that the
level is between 0.5 V and 1 V. If the calibration
accuracy is outside limits, withdraw the local
oscillator unit and reset range trimmer L2 for
optimum accuracy at the low frequency end and/or
C1 at the high frequency end. Replace the local
oscillator unit and recheck the calibration.
(3)
Switch to oscillator RANGE 3-4, tune through the
range and check that the dial calibration is within
+3% of the frequency meter reading and that the
level is between 0.6 V and 0.8 V. If the calibration
accuracy is outside limits withdraw the local
oscillator unit and reset range trimmer LA for
optimum accuracy at the low frequency end and/or
C14 at the high frequency end. Replace the local
oscillator unit and recheck the calibration.
(4)
Switch to oscillator RANGE 3-4 and turn the
CRYSTAL switch to position 1. Insert a 22 MHz
crystal into socket 1 and check that the frequency
meter reads within 22 MHz ± the crystal tolerance
after tuning the Local Oscillator to 22 MHz.
Fig. 5-2. Regulated supply measuring paints
If the voltages are not within ±1% of nominal, adjust
RV1 for -18 V or RV2 for -12 V.
5.4.5
The location of these potentiometers is illustrated in Fig.
4.1.
(2)
(3)
Local oscillator
Harmonic generator
Test equipment:- i.
Connect the wave analyser to the -18 V line and
check that the 50 Hz, 120 Hz and i80 Hz ripple
components are each less than 100 µ-V. Check
that the same components on the -12 V line are
each less than 50 -µ V.
Replace the wave analyser with the differential
voltmeter. Check that the -18 V line voltage does
not change by more than ±20 mV when the a. c.
supply is varied from 180 to 260 V, (or 90 to 130 V).
The change on the
5-5
(1)
Shunt the resistor in series with the I. F. OUT
socket by a 1 k2 resistor.
(2)
Connect the I. F. OUT socket to the R. F. • Input of
the Polyskop and the R. F. IN socket to the R. F.
Output of the Polyskop.
(3)
Set the Polyskop controls as follows:
TM 11-6625-3017-14
Output Attenuator:
Sweep Width control:
Centre Frequency
control:
Y1 Gain control:
Y1 switch:
Y2 switch:
30 or 40 dB.
maximum sweep.
frequency; the frequency blip will then be shown on the
Polyskop. It is advisable to adjust the Polyskop
frequency control and the OSCILLATOR TUNE control
together, so that the correct frequency blip remains on
the screen.
mid-way.
maximum gain.
B.
off.
(7)
Set the TF 2300 controls as follows:
SUPPLY:
Oscillator RANGE:
CRYSTAL:
on.
RANGE 5 - 8.
OFF
(4)
Adjust the OSCILLATOR TUNE control to about 88
MHz on the tuning scale, i. e. A local oscillator
frequency of 22 MHz.
(5)
Set the Frequency switch on the Polyskop to about
50-100 MHz and the Frequency Markers switch to
50 MHz.
If the sensitivity at any min is below that specified,
adjust capacitor A2bC7 and the position of the
tuning slug in coil A2bL2 to increase the amplitude
where the frequency blip is a minimum. It may also
be necessary to select a new value for A2bC14.
NOTE:
Capacitors C7 and C14 will need to be set
to a compromise position to give the best sensitivity
throughout the frequency range, as there will be more
than one minimum sensitivity point. Sensitivity becomes
approximately correct if the input attenuator on the
Polyskop can be set to the 30 or 40 dB position. While
the checks are being carried out, note that no spurious
oscillations occur.
The Polyskop screen will show a sweep between 50
and 100 MHz with the 50 MHz marker pips at each
end of the trace.
5.4.6
De-emphasis
Test equipment: j and k
The 88 MHz signal, i. e. 4th harmonic of the 22 MHz
from local oscillator, will show as a double blip at 88
MHz on the trace. Tune the local oscillator over the
frequency band, i. e. increase frequency and the
frequency blip on the Polyskop should move
towards the 100 MHz marker.
(1)
With the modulation meter switched off, disconnect
the yellow lead from the discriminator unit output
(A5, pin 4) and connect the lead to the output of the
signal source.
Range 5 on the TF 2300A covers 88-176 MHz;
therefore, when the 100 MHz blip reaches the 100
MHz marker, change the Frequency switch on the
Polyskop to 100-200 MHz and the 100 MHz blip will
appear superimposed on the 100 MHz marker at
the beginning of the trace. Continue to tune through
the range to 176 MHz:
(6)
Then tune the local oscillator through the remaining
frequency ranges up to 1000 MHz and note the
frequencies at which the frequency blip shown on
the Polyskop is a minimum and measure the
sensitivity at these points using the signal generator
and the R. F. millivoltmeter.
NOTE:
When using the Polyskop above 400 MHz,
the variable frequency control must be set to the required
frequency and the OSCILLATOR TUNE control on the
TF 2300 should be tuned to this
Fig. 5-3. Location of discriminator output lead.
5-6
TM 11-6625-3017-14
(2)
Connect the voltmeter to the OUTPUT terminals.
5.4.8
(3)
Turn the DE-EMPHASIS switch to 75 µ sec, the
Function switch to DEV+ and the MAX MOD FREQ
to 200 kHz.
Test equipment: j and k
(4)
(5)
Set the signal source frequency to 100 Hz and
adjust its output level to give a suitable reference
deflection on the output voltmeter.
Vary the signal source frequency, keeping the
output level constant, and check that the response
relative to the 100 Hz reference is within ± 1 dB of:
-3 dB at 2. 1 kHz.
-16.9 dB at 15 kHz.
(6)
Repeat step (5) with the DE-EMPHASIS switch set
to 50 µ sec and check that the response is within L.
dB of:
(1)
On the a. m. detector unit (All) disconnect the links
from pins 17 and 18. Then connect the signal
source between pins 18 and 10 (earth).
(2)
Turn the % A. M. RANGE switch to 100% and the
Function switch to A. M. PEAK.
(3)
Connect one voltmeter across the OUTPUT
terminals and another to monitor the signal source
output.
(4)
Set the signal source frequency to 10 kHz and its
output to give a reading of 100% on the TF 2300A
meter. Note the reference level on the output
voltmeter.
(5)
Vary the signal source frequency, keeping the level
constant, between 30 Hz and 50 kHz and note that
the reading on the output voltmeter is flat to within
±0. 25 dB of the reference level.
(6)
Switch off the TF 2300A, remove the test
equipment and replace the link between A11 pins
17 and 18.
-3 dB at 3. 15 kHz.
-16.9 dB at 22.5 kHz.
5.4.7
Range attenuator
Test equipment: j and k
5.4.9
(1) Connect the signal source as in step (1) of
Sect. 5.4.6.
(2)
Connect the voltmeter to monitor the signal source
output.
(3)
Turn the DEV RANGE switch to 5 kHz and the DEEMPHASIS switch to OFF.
(4)
Set the signal source frequency to 1 kHz and adjust
its output to give full-scale deflection on the TF
2300A meter.
(5)
Turn the DEV RANGE switch to 15 kHz. Increase
the signal source output by 10 dB and note that the
meter reads within 1l% of full-scale.
(6)
Repeat step (5) for the 50, 150 and 500 kHz
deviation ranges.
(7)
Switch off the TF 2300A, remove the test
equipment and reconnect the yellow lead to the
discriminator output.
A.M. and l.f. response
Discriminator trigger
Test equipment: a
5-7
(1)
With the modulation meter switched off disconnect
the lead from pin 2 on the discriminator unit (A5)
and connect the multimeter to the collector of A5Q2
(or Q3).
(2)
Switch on and adjust A5RVl to a point where the
circuit is at change of state, i.e. multimeter either
reads 0 V or 15 V. When the potentiometer is
adjusted the voltage will jump either to 15 V or 0 V
from the original reading. Set to a position just
before it jumps.
(3)
Transfer the meter to pin 7 (i. e. test point adjacent
to RV1). Note the voltage and decrease it by 0.5 V
by rotating RV1 counter-clockwise. Check that the
output waveform at the output terminals of the
instrument is free from spurious pulses. Switch off
the TF 2300A and reconnect pin 2.
TM 11-6625-3017-14
and Q6 in the discriminator (A5) and/or by selecting
a new value for A5R13.
5.4.10 Set l.f.
Test equipment: 1
5.5 REPLACEMENT OF SUB-ASSEMBLIES
(1)
Connect the crystal oscillator to the R. F. IN socket.
Oscillator
(2) Turn the oscillator RANGE switch to EXT and the
Function switch to TUNE.
(3)
Set the LEVEL control for a meter reading at the
’top end of the black R. F. LEVEL arc.
(4)
Turn the Function switch to F. M. SE.T FREQ and
adjust
A4L1
through
the
hole
in
the
limiter/discriminator cover (see Fig. 4-2) to bring the
meter reading to the SET mark.
Remove the instrument case, disconnect the plug to
the mixer unit and withdraw the lead and plug into the
oscillator compartment. Remove the chrome screws at
each corner of the oscillator front panel and slide the unit
out. To remove completely, disconnect the supply plug
from within the oscillator compartment.
When
withdrawn, all presets, coils etc., are accessible without
further dismantling.
R.F. attenuator and mixer.
5.4.11 L.F. and discriminator noise
It is not advisable to attempt any removal of these
items, the former being a sealed unit. In all cases,
contact Marconi Instruments if repair appears necessary
in this unit.
Test equipment: 1, m, n and o
(1)
Connect the 0. 014 [F capacitor, r.m.s. voltmeter
and oscilloscope across the OUTPUT terminals.
(2)
Turn the oscillator RANGE switch to EXT.
(3)
Connect the 1.5 MHz crystal oscillator to the R. F.
In socket and turn the MAX MOD FREQ switch to
15 kHz.
(4)
Turn the Function switch to SET FREQ-F. M. and
check that the TF 2300A meter deflects to the SET
mark.
(5)
Turn the Function switch to TUNE and adjust the
LEVEL control to bring the TF 2300A meter reading
to the top end of the black R. F. LEVEL arc.
(6)
Turn the Function switch to SET CAL and adjust the
r. m. s. voltmeter range switch to give a convenient
reference level. Note this reference level.
(7)
Turn the Function switch to DEV+ and the RANGE
switch to 5 kHz. Turn down the external voltmeter
range switch and check that the reading is at least
52 dB below the reference level, i. e. -72 dB relative
to the level of 50 kHz deviation.
Printed circuit boards
(8)
The following are plug in circuit boards which, apart
from A13, can be removed by pressing a spring clip and
pulling the board upwards:
(1) 1st 1. f. amplifier (A7).
(2) 2nd 1. f. amplifier (A9).
(3) A. M. detector (All).
(4) Peak reading voltmeter (A10).
(5) Calibrator (A12).
(6) Power supply unit (A13).
(This board is secured by a bracket which has to be
removed before the board can be unplugged. )
An extension board, type TM 7926, is stowed on the
inside of the rear panel. By means of this board, any of
the above can be raised above its compartment for
examination while in the operative condition.
I.F. amplifier
The complete amplifier can be removed when
necessary by unsoldering one lead and dis- connecting
two miniature plugs. Three screws retain the unit to the
chassis. Access for adjust- ment is provided by a
removable cover, thus enabling the inductors of the
tuned circuits to be adjusted through holes in the back of
the circuit boards with a trimmer tool.
If not, remove the yellow lead from the discriminator
output, A5 pin 4 (see Fig. 5-3) and check that the
noise level drops to -58 dB. A high noise figure can
be improved by selection of transistors Q3, Q4, Q5,
5-8
TM 11-6625-3017-14
(5)
Limiter and discriminator
All thirteen connections are soldered; the complete
unit can be removed after these have been unsoldered
by releasing four nuts from the top side of the chassis.
The cover is removable to give access to all the circuits
and presets.
Starting from point Y, wind the cord 7 1/2 times
counter-clockwise round the bush, take it over
pulley B, through the slot in pulley C and attach it to
the other spring at point Y’.
200 kHz and 15 kHz low-pass filters
Either of these units can be removed by unsoldering
two connections and releasing two screws. The 200 kHz
filter is adjustable through holes in the top chassis
(immediately below extension board stowage).
Oscillator drive cord
The oscillator drive cord consists of a 3 1/2 ft length
of nylon cord arranged as shown in Fig. 5-4. Before
fitting, suspend the new cord with a weight of 4 lb (2 kg)
for 24 hours.
To fit a new cord:
(1)
Turn the
clockwise.
(2)
Attach one end of the cord (X) to the correct spring
on pulley C.
(3)
(4)
OSCILLATOR
TUNE
control
fully
Fig. 5-4. Fitting drive cord
Pass the cord through the slot and once clockwise
round pulley C, then over pulley A and counterclockwise for three-quarters of a turn round the
bush to point X’.
5.6
REPLACEMENT OF COMPONENTS
Fuses
The two fuses are fitted in fuseholders in the rear
panel. FS2 must never be changed without first switching
off the main supply, or circuit damage may result.
Ease the pin in the bush clear of the hole by means
of a small screwdriver. Loop the cord into the hole
and push back the pin to anchor it.
Transistors
Transistors that are mounted in holders may need
to be selected for low noise if replaced.
5-9
TM 11-6625-3017-14
Fig. 5-5. Parts location, Mixer TM 7723
5-10
TM 11-6625-3017-14
Fig. 5-6. Parts location, Oscillator Board TM 7705
5-11
TM 11-6625-3017-14
Fig. 5-7. Parts location, Doubler and Generator Board TM 7706
5-12
TM 11-6625-3017-14
Fig. 5-8. Parts location, I.F. Amplifier ATM 7132
5-13
TM 11-6625-3017-14
Fig. 5-9. Parts location, Limiter ATM 7285
5-14
TM 11-6625-3017-14
Fig. 5-10. Parts location, Discriminator ATM 7780
5-15
TM 11-6625-3017-14
Fig. 5-11. Parts location, 1st L.F. Amplifier ATM 7223
5-16
TM 11-6625-3017-14
Fig. 5-12. Parts location, 2nd L.F. Amplifier ATM 8806
5-17
TM 11-6625-3017-14
Fig. 5-13. Parts location, Peak Reading Voltmeter ATM 8805
5-18
TM 11-6625-3017-14
Fig. 5-14. Parts location, A.M. Defector ATM 7276
5-19
TM 11-6625-3017-14
Fig. 5-15. Parts location, Calibrator ATM 7620
5-20
TM 11-6625-3017-14
Fig. 5-16. Parts location, Power Supply Board ATM 7225
5-21
TM 11-6625-3017-14
Fig. 5-17. Parts location, Component Board ATM 8742
5-22
TM 11-6625-3017-14
APPENDIX A
REFERENCES
DA Pam 310-4
Index of Technical Manuals.
TM 11-6625-537-15
Operator’s, Organizational, Field and Depot Maintenance Manual: Voltmeter, Electronic,
ME-202/U
TM 11-6625-573-14
Operator’s, Organizational, Direct and General Support
Maintenance Manual for Signal Generator,AN/GRM-50
(FSN 6625-868-8353).
TM 11-6625-2658-14
Operator’s, Organizational, Direct Support, and General Support Maintenance Manual
for Oscilloscope AN/USM-281C (NSN 6625-00-106-9622).
TM 11-6625-2953-14
Operator’s, Organizational, Direct Support, and General Support Maintenance
Manual; Multimeter AN/USM-451- (NSN 6625-01-060-6804).
TM 38-750
The Army Maintenance Management System TAMMS).
TM 740-90-1
Administrative Storage of Equipment.
TM 750-224-2
Procedures for Destruction of Electronics material to prevent Enemy Use
(Electronics Command).
TB 43-180
Calibration Requirements for the Maintenance of Army Material.
TB 385-4
Safety Precautions for Maintenance of Electrical/Electronics Equipment.
A-1/(A-2blank)
TM 11-6625-3017-14
SECTION 6
CIRCUIT DIAGRAM
CIRCUIT NOTES
1
ARRANGEMENT
The inter-unit wiring diagram, FO 6-1,
shows all sub-assembly units in
the equipment together with their
reference designators (A1, A2 etc. )
and type numbers (prefixed TM).
Components that are not on a subassembly are part of the main
chassis assembly (designated AO).
Circuit diagrams are arranged
in order of the subassembly
designations.
2.
COMPONENT VALUES
Resistors : No suffix = ohms, k = kilohms, M = megohms.
Capacitors : No suffix = microfarads, p = picofarads.
Inductors : No suffix = henries, m = millihenries, 1 = microhenries.
t : value selected during test, nominal value shown.
3.
VOLTAGES
Printed in italics. Voltages are d. c. and
relative to chassis unless otherwise indicated.
Measured with a 20 k2/V meter.
4.
SYMBOLS
arrow indicates clockwise rotation of knob.
preset component.
panel marking.
printed board tag number.
other tag.
printed board edge connector.
indicates points at same supply potential.
waveform reference number.
5.
SWITCHES
Rotary switches are drawn schematically.
Numbers or letters indicate control knob setting
as shown in the key diagrams. Sequence of
sections reading from control knob end is as
follows :1F = 1st section, front
1B = 1st section, back
2F = 2nd section, front
etc.
NOTE
FO 6-1 through 6-6 are located in back of manual
6-1/(6-2 blank)
TM 11-6625-3017-14
APPENDIX B
MAINTENANCE ALLOCATION
Section I. INTRODUCTION
system so that their functions are properly synchronized.
This does not include setting the frequency control knob
of radio receivers or transmitters to the desired
frequency.
B-1. General
This appendix provides a summary of the maintenance
operations covered in the equipment literature. It
authorizes categories of maintenance for specific
maintenance functions on repairable items and
components and the tools and equipment required to
perform each function. This appendix may be used as an
aid in planning maintenance operations.
f. Calibrate. To determine the corrections to be made
in the readings of instruments or test equipment used in
precise measurement. Consists of the comparison of two
instruments, one of which is a certified standard of
known accuracy, to detect and adjust any discrepancy in
the accuracy of the instrument being compared with the
certified standard.
B-2. Maintenance Functions
Maintenance functions will be limited to and defined as
follows:
a
Inspect. To determine serviceability of an item
by comparing its physical, mechanical, and electrical
characteristics with established standards.
g. Install. To set up for use in an operational
environment such as an encampment, site, or vehicle.
h. Replace. To replace unserviceable items with
serviceable like item.
b. Test. To verify serviceability and to detect incipient
electrical or mechanical failure by use of special
equipment such as gages, meters, etc. This is
accomplished with external test equipment and does not
include operation of the equipment and operator type
tests using internal meters or indicating devices.
i. Repair. To restore an item to serviceable condition
through correction of a specific failure of unserviceable
condition. This function includes, but is not limited to
welding,
grinding,
riveting,
straightening,
and
replacement of parts other than the trial and error
replacement of running spare type items such as fuses,
lamps, or electron tubes.
c
Service. To clean, to preserve, to charge, and to
add fuel, lubricants, cooling agents, and air. If it is
desired that elements, such as painting and lubricating,
be defined separately, they may be so listed.
j. Overhaul. Normally, the highest degree of
maintenance performed by the Army in order to minimize
time work in process is consistent with quality and
economy of operation. It consists of that maintenance
necessary to restore an item to completely serviceable
condition as prescribed by maintenance standards in
technical publications for each item of equipment.
Overhaul normally does not return an item to like new,
zero mileage, or zero hour condition.
d. Adjust. To rectify to the extent necessary to bring
into proper operating range.
e. Align. To adjust two or more components or
assemblies of an electrical or mechanical
B-1
TM 11-6625-3017-14
k. Rebuild. The highest degree of materiel
maintenance. It consists of restoring equipment as
nearly as possible to new condition in accordance with
original manufacturing standards. Rebuild is performed
only when required by operational considerations or
other paramount factors and then only at the depot
maintenance category. Rebuild reduces to zero the
hours or miles the equipment, or component thereof, has
been in use.
Code
Maintenance Category
C....................... Operator/Crew
C....................... Operator/Crew
0 ....................... Organizational Maintenance
F ....................... Direct Support Maintenance
H....................... General Support Mainteamce
D....................... Depot Maintenance
d
Column 4, Tools and Test Equipment.
Column 4 specifies, by code, those tools and test
equipment required to perform the designated function.
The numbers appearing in this column refer to specific
tool and test equipment which are identified in table I.
1. Symbols. The uppercase letter placed in
the appropriate column indicates the lowest level at
which that particular maintenance function is to be
performed.
e
B-3. Explanation of Format
Column 5, Remarks. Self-explanatory.
B-4. Explanation of Format of Table I, Tool
and Test Equipment Requirements
a. Column 1, Group Number. Column 1 lists
group numbers, the purpose of which is to identify
components, assemblies, subassemblies and modules
with the next higher assembly.
The column in Table I, Tool and Test Equipment
Requirements are as follows:
a. Tools and Equipment. The numbers in this
column coincide with the numbers used in the tools and
equipment column of the applicable tool for the
maintenance function.
b. Column 2 Functional Group. Column 2 lists
the noun names of components, assemblies,
subassemblies and modules on which maintenance is
authorized.
b.
Maintenance Category. The codes in this
column indicate the maintenance category normally
allocated the facility.
c. Column 3, Maintenance Functions. Column
3 lists the maintenance category at which performance of
the specific maintenance function is authorized.
Authorization to perform a function at any category also
includes authorization to perform that function at higher
categories. The codes used represent the various
maintenance categories as follows
:
c.
Nomenclature. This column lists tool, test,
and maintenance equipment required to perform the
maintenance functions.
d.
Federal Stock Number. This column lists
the Federal stock number of the specific tool or test
equipment.
e.
B-2
Tool Number. Not used.
TM 11-6625-3017-14
SECTION II. MAINTENANCE ALLOCATION CHART
FOR
MODULATION METER ME-505/U
(1)
GROUP
NUMBER
00
(2)
(3)
(4)
COMPONENT ASSEMBLY
MAINTENANCE
FUNCTION
MAINTENANCE CATEGORY
C
O
F
H
D
Meter, Modulation ME-505/U
Inspect
0.5
(Marconi Model TF 2300A)
Test
Test
0.9
01
Mixer Module
Al
02
Oscillator Bd
A2a
03
Harmonic Generator Bd
A2b
04
IF Amplifier Bd
A3
05
Limiter
A4
06
Discriminator
AS
07
200 k Hz Filter Bd
A6
08
Ist LP Amplifier Ed
A7
09
15 k Hz Filter Bd
AB
10
2nd LF Amplifier Bd
A9
11
Peak Reading Voltmeter Bd
A10
12
AM Detector Bd
All
13
Calibrator Bd
A12
14
Power Supply Bd
A13
15
Component Ed
A14
(5)
B-3
TOOLS AND
EQUIPMENT REMARKS
16
1.0
Repair
Repair
Replace
Overhaul
Test
Replace
Repair
Test
Replace
Repair
Test
Replace
Repair
Test
Replace
Repair
Test
Replace
Repair
Test
Replace
Repair
Test
Replace
Repair
Test
Replace
Repair
Test
Replace
Repair
Test
Replace
Repair
Test
Replace
Repair
Test
Replace
Repair
Test
Replace
Repair
Replace
Repair
Test
Replace
Repair
Test
Replace
Repair
(6)
0.5
1.5
2.0
3.0
0.5
0.3
2.0
0.7
0.3
1.0
0.7
0.3
1.0
0.4
0.2
0.8
0.4
0.3
0.8
0.5
0.3
0.7
0.5
0.2
0.6
0.5
0.2
0.6
0.5
0.2
0.7
0.5
0.3
0.6
0.5
0.2
0.8
0.5
0.2
0.6
0.5
0.2
0.6
0.2
0.5
0.5
0.2
0.3
0.2
0.2
0.3
16
1-8,10-16
16
1-8, 10-16
1-16
1-8, 10-16
1-16
1
16
1-16
5-8
16
1, 16
9
16
1, 16
1
16
1, 16
1, 3, 10
16
1, 16
4, 10.11
16
1, 16
10, 11
16
1, 3, 10
1, 16
16
1, 3, 10
11
16
1, 3, 10
1, 16
16
1, 3, 10
1, 2
16
1, 2, 16
10, 11
16
1, 3, 10
10, 11
16
1, 3, 10
16
1
1-4
16
1, 16
1, 16
16
1,16
A
B
C
TM 11-6625-3017-14
SECTION III. TOOL AND TEST EQUIPMENT REQUIREMENTS
FOR
ENCODER-DECODER KY-883/GSC
TOOL OR TEST
EQUIPMENT
REF CODE
MAINTENANCE
CATEGORY
NOMENCLATURE
NATIONAL/NATO
STOCK NUMBER
1
2
HD
HD
Multimeter AN/USM-451
Transformer, Variable Power CN-16/U
6625-00-060-6834
5950-00-235-1036
3
4
5
6
7
8
9
HD
HD
HD
HD
HD
HD
D
6625-00-845-7133
6625-00-972-4046
6625-01-061-89e8
6625-00-113-3491
10
11
12
13
14
15
16
HD
HD
HD
HD
HD
HD
0
Wave Analyzer TS-1830D/U
Differential Voltmeter NE-202/U
Frequency Counter AN/USM-459
RF Millivoltmeter ME-426/U
T Connector (All BNC)
Crystals, frequencies 22, 23, and 44 MHz
Response Analyzer 4-1000 MHz
(Rhode & Schwarz ’Poly Skop’ SWOB II)
Signal Generator AN/GRM-50C
Sensitive Voltmeter ME-370/U
RMS Voltmeter AN/USM-224
Oscilloscope AN/USM-281C
Signal Generator HP-8660C
Tool Kit TK-100
Tools and Test Equipment available to the
repair person for his/her assigned mission.
B-4
6625-00-003-3238
6625-00-135-6990
6625-00-727-47D6
6625-00-106-9622
6625-00-689-6787
5180-00-605-0079
TOOL
NUMBER
TM 11 6625-3017-14
SECTION IV. REMARKS
REFERENCE
CODE
REMARKS
A
Replacement of knobs, fuses and lamps.
B
Repaired by replacement of boards.
C
Repair boards.
B-5
By Order of the Secretary of the Army:
E. C. MEYER
General, United States Army
Chief of Staff
Official
ROBERT M. JOYCE
Brigadier General, Unites States Army
The Adjutant General
DISTRIBUTION:
To be distributed in accordance with special mailing list.
TM 11-6625-3017-14
FO Fig. 6-1. Chassis inter-unit wiring
TM 11-6625-3017-14
FO Fig. 6-2. Mixer, oscillator and i.f. amplifier
TM 11-6625-3017-14
FO Fig. 6-3. Limiter, discriminator and 1st l.f. amplifier
TM 11-6625-3017-14
FO Fig. 6-4. 2nd l.f. amplifier and peak reading voltmeter
TM 11-6625-3017-14
FO Fig. 6-5. A.M. detector and calibrator
TM 11-6625-3017-14
2300A (USA)
JAN 1974
FO Fig. 6-6. Power supply unit
PIN: 049597-000
This fine document...
Was brought to you by me:
Liberated Manuals -- free army and government manuals
Why do I do it? I am tired of sleazy CD-ROM sellers, who take publicly
available information, slap “watermarks” and other junk on it, and sell it.
Those masters of search engine manipulation make sure that their sites that
sell free information, come up first in search engines. They did not create it...
They did not even scan it... Why should they get your money? Why are not
letting you give those free manuals to your friends?
I am setting this document FREE. This document was made by the US
Government and is NOT protected by Copyright. Feel free to share,
republish, sell and so on.
I am not asking you for donations, fees or handouts. If you can, please
provide a link to liberatedmanuals.com, so that free manuals come up first in
search engines:
<A HREF=http://www.liberatedmanuals.com/>Free Military and Government Manuals</A>
– Sincerely
Igor Chudov
http://igor.chudov.com/
Download PDF