Broadcast Equipment FMM-1 FM Monitor

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Broadcast Equipment

FMM -1
FM MONITOR

WARRANTY AND ASSISTANCE

All Belar products are warranted against defects in materials and
workmanship. This warranty applies for one year from the date or
delivery, or, in the case of certain major components listed in the
instruction manual, for the specified period. Belar will repair or
replace products which prove to be defective during the warranty
period provided that they are returned to Belar. No_ other
warranty is expressed or implied. Belar is not liable’ for
consequential damages.

For any assistance, contact either your Belar Sales Representative
or Customer Engineering Service at the Belar factory.

» Broadcast Equipment

Instructions

FMM-1
FM Monitor

BELAR ELECTRONICS LABORATORY, INC.

TABLE OF CONTENTS

SECTION 1 PAGE SECTION 5 PAGE

GENERAL INFORMATION: © .c)5 9243.2 3 eee 3 MAINTENANCE. ore. E8 ott cn eke sta to 15
1—1 GENERAL DESCRIPTIONS 3 eee 3 5—1 INTRODUCTION Sh eee ee 15
1—2 PHYSICAL DESCRIPTION 2 ae eee 3 5-2 PERFORMANCE CHECKS). 30. 2 ee 18
1—3 ELECTRIGAL DESERIPTIONS ee ee 4 5-2-1 Power and Oven Check” 2. 25.5), see 15
1—4 ELECTRICAL SPEGIFICATIONS.. 3 7 4 5-2-2 Oscillator Level’ Check \o% 2 4), coe ee 15
1—5 MECHANICAL SPECIFICATIONS... 2. 32. 5 5-2-3 Frequency Meter Amplifier Check ...... 15
1-6 INSTRUMENT IDENTIFICATION ....... 5 5-2-4 Freq Meter Discriminator Check ....... 15
1-7 AGGESSO RIES “0 ecco hea 2 teen 5 5-2-5 Mod Meter Amplifier Zero Check ...... 18
5—2—6 Modulation Calibrator Check .......... 15
SECTION 2 PAGE 5-2-7 Remote Meter Switch Check .......... 15
INSTALELA BION eae ey, eters cit cecho nes ea as Geen 7 5—2-8 Percent Mod Potentiometer Check ...... 15
2-1 INET IAL INSPECTION (ce ete ene q | 5-2-9 Modulation Polarity: Check ... . 2. .8e 15
2-2 CLAIMS 2) bic. oct ek haere is ae eee 7 5—2—10-)» Carrier Level Check” 2... .4\ 2905 ss ee 15
2-3 REPACKING FOR SHIPMENTS ........ 7 5=2—11 Operate Check) <0). 3)i8- 4 se 15
2—4 PREPARATION, FOR: USES. 32 fo eee 7, 5—2—12 De-emphasis Switch Check ........... 16
5-3 ADJUSTMENTS, CALIBRATION &
SECTION 3 PAGE TROUBLESHOOTING 224. =e 16
OPERATIONS «32.2 .c3a.c de be sk ee 9 ho- | Power. & Oven» 2... 8,02 bee 16
3-1 INITIAL OPERATION... 4. eee 9 5—3-—2 Oscillator Cevel pore fre eo. eee 16
3-2 NORMAL OPERAMON 22.8) sea 9 5-3-3 Frequency Meter Amplifier ........... 16
3-3 LOCAL OSCILLATOR 5-3-4 Freq Meter Discriminator —. 2). eee 16
FREQUENCY CALIBRATION 33222: 9 5—3—5 Mod Meter Amplifier Zero ........... 16
3—4 TRANSMITTER MEASUREMENTS .. 72%... 9 5-3-6 Modulation Calibratows ae. Jo. >< >see V7
5-3-7 Remote Meter Switch .... 5... 22. o32e 17
SECTION 4 PAGE 5—3-—8 Percent Mod Potentiometer........... 17
PRINCIPLES OF OPERATIONS] -708 (0 ceotee ne eee 11 5-3-9 Modulation? Polarityi.. “Stat. 4. eee 7
4-1 BLOCK DIAGRAM DESCRIPTION ..... 11 5—3—10». Carriers Level... oh 25s apie ae 17
4—2 DETAILEDZCIRCULTE DESGRIPMONS el 53-11 ‘Operate, ioicc s+ s Se 015s ee ee 17
4—2-1 Oscillator, Tripler & Mixer Circuit ...... 11 5—3—12 De-emphasis Switch .........). 5 see 17
4—2-—2 Oscillator, Counter Discriminator
&Amplitier Circuits eee .cs eee 13 SECTION 6 PAGE
4—2—3 Amplifier, Metering & REPLACEABEE PARES: (see tees cn 23
Flasher: CircultS 205) 22 ge eee ee 14 6-1 INTRODUCTION) oso a5. oe 23
6-2 ORDERING INFORMATION ......... 23
SECTION 7 PAGE
SCHEMATICS ©.) 0: a's 52 fee ee ee 29
LIST OF ILLUSTRATIONS
1—1 FMM—1 FREQUENCY AND 5-3 A3 GARD oo cnt: Suen «le dee 20
MODULATION MONITOR .......... 3 5—4 TOP VIEW? COVER*°OFF 3.24...) ee 21
1-2 FRONT PANELAVIEW 5 see eee 4 5-5 BOTTOM VIEW, COVER OFF . 22 sae 22
1—3 REAR«< PANEL VIEW 3.) 2 eee 4 7-1 OSCILLATOR, TRIPLER & MIXER
1—4 MECHANICAL DIMENSIONS .......... 5 CARD. AT, SCHEMATIC... 72. 2 ee 30
2-1 REAR PANEL CONNECTIONS ........ 6 7-2 OSCILLATOR, COUNTER & AMPLIFIER
3-1 OPERATING GONTROLS) = 3: . Stee 8 CARD A2. SCHEMATIC =... 2 Sf) ee at
4—1 BLOCK DIAGRAM 0.047.440 cae 10 7-3 AMPLIFIER, METERING & FLASHER .
4—2 WAVEFORMS 3 “A; enok Soaeee eee 12 CARD *A3; SCHEMATIC + ....5 eee 3a
5—1 ACARD on. 2. ooo Ae 18 7-4 FREQUENCY & MODULATION MONITOR
5-2 A2 CARD) a2 fi cae tk ee 19 CHASSIS, SCHEMATIC .72. 5. 35

SECTION 1
GENERAL INFORMATION

1—1 GENERAL DESCRIPTION

The Belar FMM—1 FM Frequency and Modulation Monitor,
Figure 1—1, [FCC Type Approval Number 3—129] is a
wideband, all solid state FM monitor designed to meet the
Federal Communications Commission requirements for
measuring the center frequency and total modulation
characteristics of monaural as well as multiplexed FM
transmitters having a center frequency range of 88 to 108
‘MHz. In addition, the FMM—1 may be used as a low
distortion and low noise FM demodulator for driving audio
monitor amplifiers and the companion Belar FMS—1 Stereo
Frequency and Modulation Monitor and one or more
SCM—1 SCA Frequency and Modulation Monitors. The
FMM—1 incorporates a deviation type modulation
calibrator to insure the accuracy of the modulation readings
at any time.

MODULATION

1—2 PHYSICAL DESCRIPTION

The FMM—1, Figure 1—2, is constructed on a standard 5%
x 19 inch rack mount. Seldom used controls and test points
are located under the hinged front cover bar. Factory
adjustments are located within the shielded compartments
of the monitor. The AC power input, RF input, and
monitor outputs are located at the rear of the FMM—1
chassis on individual connectors or on rear terminal blocks
as shown in Figure 1—3. The FMM—1 is completely solid
state utilizing all silicon transistors for long, trouble-free
life. The individual circuits are constructed on military
grade, glass-epoxy, plated printed circuit boards. High
reliability industrial and military grade components are
used throughhout.

Figure 1—1

1—3 ELECTRICAL DESCRIPTION

The FMM—1 is a solid state, low sensitivity, crystal
controlled, superheterodyne FM receiver incorporating a
highly linear and stable pulse counting discriminator that
measures the center frequency deviation and demodulates
the FM transmission. Various metering and testing
provisions are contained within the monitor to measure
transmitter output characteristics. These provisions include
a center frequency deviation meter; a peak reading total
modulation meter, switchable to either positive or negative
modulation polarity; a peak modulation light, independent
of modulation polarity, that responds to both positive and
negative directions; metering circuits to set the incoming
RF level and to standardize the center frequency deviation
meter with the calibrating oscillator; a deviation type
modulation calibrator to standardize the modulation level.
Outputs obtained from the monitor include a monaural
output for aural monitoring, a distortion meter test output
[both monaural output and distortion meter output have
front panel switched de-emphasis] , a wideband test output,
four wideband outputs for driving associated muitiplex
demodulators, an AM noise diode output, and an incidental
AM noise diode output. FCC Type Approved remote
metering of the FMM—1 may be externally provided for the

center frequency deviation meter, modulation meter, and
peak light. :

1—4 ELECTRICAL SPECIFICATIONS

REWnput Sensitivitye. owe ee eee eee 0.2 to 10 volts RMS.
REI nputlimpedance 20. . Wier: ot. ree che eee 50 ohms.
RF Frequency*Range : e.5,.-0 2 oe rene eee 88—108 MHz.
Deviation*Meter! Range: 1,2 ino se ape os te eee ee ee +3 kHz

SPs ic cee ae 133% [100% at 75 kHz].
Oe Sabed MRAP tin gg ts oe Mtl 100% at 75 kHz.
Modulation Meter Accuracy ..... Better than 5% over entire scale.
Peak Modulation Indicator 50 to 120%.
Rat ratte a nS Te ae + 0.1 db, 50—75,000 Hz,
3 db down at 180 kHz.

Modulation Meter Range
Modulation Calibrator

Frequency response

Distortion: ci? Sacks Oe Sieepanle eee 0.1% max. 50—75,000 Hz.
Signal-to-Noise Ratio ......... 75 db with 75 usec de-emphasis.
Outputs te. Shee Rune eae ane 4 wideband isolated outputs to

drive the FMS—1 stereo unit and one or more SCM—1
SCA units, wideband test output, distortion meter
output, aural monitoring output, AM noise output,
and Incidental AM noise output.

sia eyearsh ante Both carrier deviation and modulation
meters may be remotely metered, 5000

ohms external loop resistance.

Remote Metering

Figure 1—2

FREQUENCY AND MODULATION MONITOR

MODEL FMM-1 SER. NO.

FCC TYPE APPROVAL NO. 3-129
BELAR ELECTRONICS LABORATORY, INC.
UPPER DARBY, PENNSYLVANIA

COMPOSITE OUTPUT
Ji v2 J3 J4

NOC DOAOAODHOO?
i) & @ G) @ ©) @) @ yy G )
oN tat FY }

Jo aa)

Js v6

POWER
oF 2 3

—re®
RIB v7

_ecoorr = Se Hee

r-AM—

Figure 1—3

SIDE VIEW

FRONT VIEW

Figure 1—4

1—5 MECHANICAL SPECIFICATIONS

DURWESTOE 4.5) bls. cud cea nection Bie 5% x 19 x 11 7/8 inches overall
DETAICGIDIMENSIONS cashes ietese fo ceo chawtoeeeks bas Glee Figure 1—4
INCtaVVCIGI teense ca aan crcl vnsicies pene mee nce, Suams etn ke erate 15 pounds
SHIPPIMGWVeIGh terme aces then eri eric hiveve ore ce eee ane 19 pounds

1—6 INSTRUMENT IDENTIFICATION

The instrument is identified by the model number and a six
digit serial number. The model number and serial number
appear on a plate located on the rear panel, Figure 1—3. All
correspondence to your Belar representative or to the Belar
factory in regard to the instrument should reference the

model number and complete serial number.
1—7 ACCESSORIES

The Belar FMM—1 FM Frequency and Modulation Monitor
may be used for the remote monitoring of an FM
transmitter with either the Belar MP—1 Remote Meter
Panel or the Belar RFA—1 RF Amplifier. The MP—1 Meter
Panel contains a peak indicator lamp, a carrier frequency
deviation meter and a modulation meter, both designed for
5000 ohms loop resistance. The RFA—1 RF Amplifier
provides pre-amplification and selectivity to permit direct
off-air monitoring with the FMM-1.

SLAdLNO ALISOdWOD

SdD 09-05 -ASLL

STEREO

INC. A.M.

A.M.

Rieke

SCA

NOISE

INPUT

GROUND
MONITOR OUTPUT
+25V

4+25V
i}
REMOTE
. MOD. METER
+ REMOTE
| FREQ. METER
EXT. MOD.
PEAK LIGHT

19VAC

OS wed ao Sieh. Sore

S
S
S
AY
8S
S
mw
NY
S
S
S
S

GROUND

él

VSe° Ws"
ed

Figure 2—1

SECTION 2
INSTALLATION

2—1 INITIAL INSPECTION

Check the shipping carton for external damage. If the
carton exhibits evidence of abuse in handling [holes,
broken corners, etc.] , ask the carrier’s agent to be present
when the unit is unpacked. Carefully unpack the unit to
avoid damaging the equipment through use of careless
procedures. Inspect all equipment for physical damage
immediately after unpacking. Bent or broken parts, dents
and scratches should be noted. If damage is found, refer to
Paragraph 2—2 for the recommended claim procedure.
Keep all packing material for proof of damage claim or for
possible future use.

2—2 CLAIMS

If the unit has been damaged, notify the carrier
immediately. File a claim with the carrier or transportation
company and advise Belar of such action to arrange the
repair or replacement of the unit without waiting for a
claim to be settled with the carrier.

2—3 REPACKING FOR SHIPMENT

If the unit is to be returned to Belar, attach a tag to it

showing owner and owner’s address. A description of the

service required should be included on the tag. The original

shipping carton and packaging materials should be used for

reshipment. If they are not available or reusable, the unit
should be repackaged in the following manner:

a. Use a double-walled carton with a minimum test
strength of 275 pounds.

b. Use heavy paper or sheets of cardboard to protect all
surfaces.

c. Use at least 4 inches of tightly packed, industry
approved, shock absorbing material such as extra firm
polyurethane foam or rubberized hair. NEWSPAPER IS
NOT SUFFICIENT FOR CUSHIONING MATERIAL.

d. Use heavy duty shipping tape to secure the outside of
the carton.

e. Use large FRAGILE labels on each surface.

f. Return the unit, freight prepaid, via air freight. Be sure
to insure the unit for full value.

2—4 PREPARATION FOR USE

The FMM—1 Frequency and Modulation Monitor is
designed to be mounted in a standard 19-inch rack mount.
When mounted in a rack, a slight air space should be
provided above and below the unit as the heat generated by
the crystal oven should be dissipated. When the monitor is
mounted above high heat generation equipment such as
vacuum-tube power supplies, consideration should be given
to cooling requirements which allow a free movement of
cooler air through and around the FMM—1. In no instance
should the ambient chassis temperature be allowed to rise
above 50 degrees C [122 degrees F] . Mount the FMM—1 to
the rack mount using four No. 10 screws and four No. 10
countersunk finishing washers.

The Model FMM—1 requires a 105 to 125 VAC single
phase, 50 to 60 Hz power source. Consult Belar for
operation with other power sources. Attach a three wire,
grounded line cord to TB1 with the ground wire to terminal
2 and the AC line wires to terminals 1 and 3.

Connect a 50 ohm coaxial cable [RG—58] between the
monitor probe on the transmitter [or RF amplifier] and
the RF input connector J7, at the rear of the main chassis.

CAUTION: DO NOT APPLY MORE THAN 10 VOLTS RF
TO THE MONITOR OR THE RF INPUT LEVEL
CONTROL MAY BE DAMAGED.

If desired, connect external aural monitoring amplifier to
terminals 1 and 2 on TB2. Note that this is an unbalanced
600 ohm output with terminal 1 grounded. A remote
center frequency deviation meter and remote modulation
meter may be connected to terminals 7, 8 and 5, 6
respectively, if desired. Observe the proper polarities
[terminals 6 and 7 are positive] and note that the external
loop resistance not including meters must be 5000 ohms.
These meters must be obtained from Belar Electronics
Laboratory, Inc. in order to comply with FCC regulations
on remote metering. A remote peak modulation lamp may
be connected to terminals 9 and 10. CAUTION: DO NOT
SHORT TERMINAL 9 TO GROUND. The remote meters
and lamp are contained in the MP—1 Remote Meter Panel.

DS3 - POWER LIGHT

DS1 - OVEN LIGHT

M1 - FREQ..METER

S6 - CAR. LEVEL

S5 - REMOTE METERS

$7 - OSC. LEVEL

J8 - AUDIO TEST

J9 - WIDE BAND TEST

C5 - FREQ. ADJ.

$2 - FREQ. CAL.

DS2 - PEAK MOD. LIGHT

R9 - % MOD. POT. S4 - MOD. POLARITY
M2 - MOD. METER S3 - DE-EMPH.
é wes

R7 - AMP. BAL.

R6 - FREQ. CAL.

S2 - AMP. BAL.

S2 - MOD. CAL.

R8 - MOD. METER ZERO

Figure 3—1

1. POWER SWITCH—When depressed turns the unit on. Power is
applied to the crystal oven from the line and is independent of the
power switch.

2. POWER INDICATOR—Lower amber light between the meters
indicates that the unit is turned on.

3. OVEN INDICATOR—Upper red light between the meters
indicates that heat is being applied in the crystal oven.

4. RF SWITCH—When depressed indicates the RF level on the
percentage modulation meter.

5. REMOTE SWITCH—When in off [released] position removes
both metering circuits from the remote metering terminals and
substitutes the equivalent resistances.

6. OSCILLATOR SWITCH—When depressed indicates the oscillator
level on the percentage modulation meter.

7. FUNCTION SWITCH—When in OP position disables all
calibration circuits and places the unit in operation for measuring
frequency deviation and total modulation.

8. FUNCTION SWITCH—When in AMP BAL position, the inputs to
the frequency differential amplifier are shorted, allowing it to be
calibrated.

9. FUNCTION SWITCH—When in FREQ CAL position, the 650
kHz calibrating oscillator is turned on and applied to the pulse
counter frequency discriminator allowing it to be calibrated.

10. FUNCTION SWITCH—When in MOD CAL position applies a
standard deviation to the monitor to check modulation calibration.

11. FREQ ZERO POTENTIOMETER-Standardizes the width of

the output pulse of the pulse counter discriminator to read zero in
function 9 above.

12. AMP BALANCE POTENTIOMETER—Adijusts the DC balance
of the frequency differential amplifier in function 8 above.

13. MOD METER BALANCE—Adjusts the percentage modulation
meter to read zero with no modulation.

14. DE-EMPHASIS SWITCH—When released removes the 75 usec
de-emphasis from the monitoring amplifier. This is also effective on
the audio test output jack.

15. POLARITY SWITCH—Allows the percentage modulation meter
to read either positive or negative modulation polarities. Depressed
it reads positive, released it reads negative polarities.

16. PERCENT—MODULATION POTENTIOMETER—Pre-sets the
peak modulation lamp to flash at the indicated modulation setting.
This circuit is independent of modulation polarity and can be
activated by either a positive or negative modulation peak or both.

17. WIDEBAND TEST JACK—Parallels the wideband outputs to
the Add-On FMS—1 Stereo and SCM—1 SCA units. Permits tests to
be made on the output of the counter-discriminator such as linearity
and stereo composite waveform tests.

18. AUDIO TEST JACK—Test output from the monitoring
amplifier. Permits linearity tests, frequency response tests, and FM
noise tests to be made from the front panel, with de-emphasis in or
out according to function 14.

19. FREQ ADJUST—Adjusts the frequency of the local oscillator.
THIS MUST BE ADJUSTED WITH AN INSULATED ALIGNMENT
SCREWDRIVER.

SECTION 3
OPERATION

3—1 INITIAL OPERATION

The following procedure should be followed for placing the
unit into initial operation. Refer to Figure 3—1 for location
of the control functions:

1. Before turning the unit on, depress the AMP BAL switch
and release the REMOTE METER switch.

2. Depress the POWER switch and allow a 15 minute
warm-up.

3. Depress the OSC switch; the reading on the percentage
modulation meter should be approximately 100% or more.

4. Turn the RF level control on the back of unit maximum
counterclockwise. Apply RF input to the RF input jack.
Depress the RF switch and adjust the RF level control until
the percentage modulation meter reads 100%. The monitor
will operate with as little as 20%, but for AM noise
calibration, the 100% level is used.

5. With the function switch in AMP BAL, adjust AMP BAL
POTENTIOMETER to read center zero on the carrier
deviation meter and adjust the MOD ZERO
POTENTIOMETER to read zero on the modulation meter.

6. With the function switch in FREQ, adjust FREQ CAL
POTENTIOMETER to read center zero on the carrier
deviation meter.

7. Depress the MOD CAL switch; the modulation meter
will read 100% to verify the accuracy of the calibration.

8. Depress OP switch and the monitor is now ready for
operation.

3—2 NORMAL OPERATION

For normal operation, leave the FMM—1 in OP [operate]
position. Changes in RF level will not affect the accuracy of
the unit. It may be necessary to occasionally adjust the
FREQ CAL POTENTIOMETER as in step 3—1—6 above.

The PEAK MOD POTENTIOMETER is usually set to 100%
so that the PEAK LIGHT will flash at a modulation peak of

100% or greater. Since this indicator is independent of
modulation polarity [i.e., it responds to both positive and
negative peaks], it may flash when the modulation meter
does not indicate the peak. The modulation meter polarity
is switched by S4.

Note that when the MOD CAL switch is depressed, the
calibrating signal is applied not only to the metering circuit
but also to the peak light and monitoring amplifier. Hence
the 60 Hertz square wave tone will be heard in an aural
monitoring amplifier.

3—3 LOCAL OSCILLATOR
FREQUENCY CALIBRATION

The FMM-—1 is furnished adjusted to the customer’s
frequency. The monitor may be calibrated against an
external frequency standard as follows: The transmitter is
first set exactly to the assigned frequency using an outside
frequency measuring service. Measure transmitter frequency
as per steps 5, 6 and 8 under OPERATION, Paragraph 3—1.
If the indicated center frequency deviation is not zero, the
local oscillator frequency may be adjusted with the crystal
tuning capacitor C5 [through the front panel] to bring the
deviation to zero.

3—4 TRANSMITTER MEASUREMENTS

Normal transmitter proof-of-performance measurements
may be made with the FMM—1. Frequency response,
distortion, and noise measurements may be made through
the front panel AUDIO TEST jack J8. Five volts RMS is
available at 100% modulation so that most distortion and
noise analyzers may be used. Measurements may be made
with or without de-emphasis by activation of S3. The
modulation meter has a flat frequency response
characteristic so that with a pre-emphasized transmitter, the
audio input level will have to be adjusted according to the
standard 75 usec pre-emphasis curve.

AM noise measurements may be made at J6 on the back
panel. With the RF level at 100%, the normal output of J6
for 100% AM is 0 db [0.78 volts] into a high impedance
[500K or greater] . Hence a standard AC voltmeter such as
contained in a distortion analyzer may be used.

OSCILLATOR-MIXER

; ASSEMBLY At : k bite ct 5
| |

| |

: |

RF
Rr KMPLIFIER
88-108 MHZ ae

FREQUENCY
TRIPLER
87-108 MHZ
a2

CRYSTAL
OSCILLATOR
29-36 MHZ

1 2 3 4

BASEBAND OUTPUTS

MODULATION
Joe) METER

PRE-REGULATED ieee
POWER SUPPLY es".
Q1,,027,03

Figure 4—1

SECTION 4
PRINCIPLES OF OPERATION

4—1 BLOCK DIAGRAM DESCRIPTION

Figure 4—1 is a simplified block diagram of the FMM—1
FM Frequency and Modulation Monitor. The signa! paths
are shown but the detailed switching circuitry has been
omitted for clarity.

The incoming RF sample is applied to the mixer, A103,
along with the tripled local oscillator frequency to form an
intermediate frequency [IF] of 650 kHz. This signal is a
fully modulated FM signal [Figure 4—2—1] centered
around 650 kHz and is applied to the pulse-counter
discriminator assembly Card A2.

The limiter amplifies and removes any AM component from
the IF signal. The signal is squared by the Schmitt trigger,
whose output is differentiated to form a sharp trigger
[Figures 4—2—2 and 6] to drive the monostable
multivibrator, A206, 7 and 8. The monostable
multivibrator generates a pulse of fixed length and
amplitude [Figure 4—2—3] each time it receives a trigger.
Thus the output of the multivibrator is a series of pulses
with a fixed length and amplitude whose spacing depends
on the incoming frequency. Figure 4—2—7 illustrates this
output with an FM modulated signal. Note how the spacing
increases and decreases as the frequency is deviated about
650 kHz. This output is integrated by the low-pass filter
whose average AC output is equivalent to the original FM
modulation. The output of the monostable multivibrator is
also applied to the buffer amplifier A209 and integrated by
an RC network to provide an average DC signal
proportional to the carrier center frequency.

This DC signal is amplified by the differential amplifier and
applied to the carrier deviation meter. The output of the
integrating filter is amplified and applied to the modulation
metering and peak flasher circuits on Card A3.

The modulation metering circuit consists of a phase splitter
to allow either the positive or negative modulation polarity
to be selected, a feedback amplifier, a peak diode detector
circuit, and current amplifier to drive the modulation
meter. The peak diode detector circuit has a very short
charging time constant to allow the modulation meter to
accurately respond to complex waveforms of multiplex
‘signals as well as short duration bursts of program material.

The flasher circuit consists of an amplifier, phase splitter,
Schmitt voltage comparator, and monostable multivibrator.
The signal is split by the phase inverter and both phases are
applied to the Schmitt comparator which has a dual input.
The comparator will only respond to positive levels that
exceed a given value determined by the setting of the
percent modulation control. But since the phase inverter
inverts the negative modulation, each input of the
comparator receives a positive going signal—one

corresponding to the positive modulation and one
corresponding to the negative modulation, thus making it
independent of modulation polarity. Each time the level
exceeds the pre-set level, the Schmitt comparator supplies a
pulse to the monostable multivibrator. The width of the
pulse formed by the multivibrator is set to 3 seconds
duration as required by the FCC. The multivibrator turns
on the transistor switch A309 to allow the peak lamp to
flash.

The monitoring amplifier is a feedback amplifier with
push-pull output to provide a low distortion signal for aural
monitoring and audio tests. De-emphasis is accomplished by
controlling the frequency response of the internal gain and
feedback loop.

The supply voltage is regulated to 25 volts by the
pre-regulator [01, 02, and CR6]. The supply to the pulse
counter and oscillator mixer circuits is further regulated by
the precision 15 volt regulator [A2018, A2019, A2Q020,
and A2CR9Q].

4—2 DETAILED CIRCUIT DESCRIPTION

4—2—1 OSCILLATOR, TRIPLER
AND MIXER CIRCUIT

The incoming RF is attenuated by R18 [RF level] and
applied to pin 5 of the Oscillator, Tripler and Mixer Card.
Diodes A1CR1 and A1CR2 prevent excessive RF levels
from overloading the FET mixer A103. Diode A1CR3 is
used to measure the RF level and its DC output is applied
to the modulation meter when S6 [CARRIER LEVEL] is
depressed.

The crystal oscillator is a modified Clapp-Gouriet oscillator.
This type of oscillator circuit is known for its frequency
stability. The feedback ratio is determined by the ratio of
A1iC3 and A1C4. Since these capacitors are large in
comparison to the transistor A101 capacities, the transistor
has little effect on the frequency. The crystal is connected
to pins 7 and 8.

The series tuned circuit A1C1, A1L1 forces the crystal to
operate in the third overtone mode. The crystal is stabilized
at a temperature of 75 degrees C by the oven Y1. Variable
Capacitor C5 [FREQUENCY ADJUST] adjusts the crystal
frequency to that required by the channel frequency.

The output of the crystal oscillator is multiplied by 3 in the
tripler stage A1Q2. Its final frequency is then 650 kHz
above the incoming RF carrier frequency and is mixed in
A103 to produce a difference frequency of 650 kHz. The
output of the mixer is filtered by the low-pass filter A1C12,
A1RFC85, and the cable capacity interconnecting pin 2 to
the input of Card A2.

OSCILLATOR-MIXER
ASSEMBLY A1 :

COUNTER ASSEMBLY A2

RF
65
INPUT aes : pies AAS eee SCHMITT MONOSTABLE eee LOWPASS ence
88-108 MHZ , ae TRIGGER MULTIVIBRATOR shi FILTER Aah as
04, a5 Q6, Q7, a8 FL1
FREQUENCY
TRIPLER CRYSTAL ee DIFFERENTIAL
FREQ.
87-108 MHZ OSCILLATOR SE Ses BUFFER AMP
Q2 650 KHZ

Q18, Q19, Q20
Q1

Qg Q13, Q14, Q15 DEV.
Q16, Q17

CRYSTAL
OSCILLATOR
29-36 MHZ
Q1

AMPLIFIER ASSEMBLY A3

BASEBAND OUTPUTS

VOLTMETER PEAK
AMPLIFIER RECTIFIER
Q2, Q3, 04 CR1

PHASE
SPLITTER
Q1

AMPLIFIER MODULATION

METER

+25V 05, a6

SCHMITT MONOSTABLE LAMP
COMPARATOR MULTIVIBRATOR SWITCH
OneonZ Q7, Q8 Qg

PHASE
SPLITTER
Q13

PRE-REGULATED
POWER SUPPLY
Q1, Q2, Q3

PEAK
LIGHT

MONITOR
AMPLIFIER
Q15, O16

PERCENT
MODULATION

Figure 4—1

SECTION 4
PRINCIPLES OF OPERATION

4—1 BLOCK DIAGRAM DESCRIPTION

Figure 4—1 is a simplified block diagram of the FMM—1
FM Frequency and Modulation Monitor. The signal! paths
are shown but the detailed switching circuitry has been
omitted for clarity.

The limiter amplifies and removes any AM component from
the IF signal. The signal is squared by the Schmitt trigger,
whose output is differentiated to form a sharp trigger
[Figures 4—2—2 and 6] to drive the monostable
multivibrator, A2Q6, 7 and 8. The monostable
multivibrator generates a pulse of fixed length and
amplitude [Figure 4—2—3] each time it receives a trigger.
Thus the output of the multivibrator is a series of pulses
with a fixed length and amplitude whose spacing depends
on the incoming frequency. Figure 4—2—7 illustrates this
output with an FM modulated signal. Note how the spacing
increases and decreases as the frequency is deviated about
650 kHz. This output is integrated by the low-pass filter
whose average AC output is equivalent to the original FM
modulation. The output of the monostable multivibrator is
also applied to the buffer amplifier A209 and integrated by
~ an RC network to provide an average DC signal
proportional to the carrier center frequency.

The modulation metering circuit consists of a phase splitter
to allow either the positive or negative modulation polarity
to be selected, a feedback amplifier, a peak diode detector
circuit, and current amplifier to drive the modulation
meter. The peak diode detector circuit has a very short
charging time constant to allow the modulation meter to
accurately respond to complex waveforms of multiplex
signals as well as short duration bursts of program material.

4—2 DETAILED CIRCUIT DESCRIPTION

4—2—1 OSCILLATOR, TRIPLER
AND MIXER CIRCUIT

The crystal oscillator is a modified Clapp-Gouriet oscillator.
This type of oscillator circuit is known for its frequency
stability. The feedback ratio is determined by the ratio of
A1C3 and A1C4. Since these capacitors are large in
comparison to the transistor A101 capacities, the transistor
has little effect on the frequency. The crystal is connected
to pins 7 and 8.

The output of the crystal oscillator is multiplied by 3 in the
tripler stage A1Q2. Its final frequency is then 650 kHz
above the incoming RF carrier frequency and is mixed in
A103 to produce a difference frequency of 650 kHz. The
output of the mixer is filtered by the low-pass filter A1C12,
A1RFC5, and the cable capacity interconnecting pin 2 to
the input of Card A2.

Figure 4—2

4—2—2 OSCILLATOR, COUNTER
DISCRIMINATOR AND AMPLIFIER
CIRCUITS

When the operate [OP] switch S2 is depressed, 15 VDC
from pin 7 is applied to pin 4 to turn on diode A2CR1 so
that the 650 kHz intermediate frequency, Figure 4—2—1, is
applied to the limiter, A2Q2 and 3. This stage amplifies and
removes any amplitude modulation component that may be
present on the signal. The Schmitt trigger A204 and 5
squares the signal by developing a pulse each time the signal
crosses the zero axis in the positive direction. The output of
the Schmitt trigger is differentiated, Figure 4—2—2, and
applied to the monostable multivibrator, A2Q6, 7, and 8
through diode A2CR4.

The monostable multivibrator differs from the conventional
multivibrator in that the timing capacitor A2C16 is charged
through a constant current source, A2Q7, instead of a
resistor. Zener Diode A2CR5 regulates the voltage to the
base of transistor A2Q7, and silicon diode A2CR6 provides
temperature compensation for the emitter-base junction of
A2Q7. Potentiometer, R6 [FREO CAL], in series with R5
[COARSE FREQUENCY CAL] connects the pins 9 and 10
to set the current through A2Q7. The current through
A2Q7 sets the slope of the charging current of the timing
capacitor A2C16 which determines the pulse width of the
multivibrator. This modification of the multivibrator
greatly increases both its stability and linearity when used
as a pulse counter discriminator.

The output of the monostable multivibrator, Figure
4—2-—3, is buffered by an emitter follower A2Q10 and is
integrated by the low-pass filter FL1, Figure 4—2—4. This
filter counts [averages] the number of pulses over a unit
time interval by filtering out the 650 kHz pulses and only
passing the modulation, Figure 4—2—9. The output of the
low-pass filter is amplified by A2011 and buffered by the
emitter follower A2012. The modulation output [baseband
output] is taken off pin 12 to drive subsequent portions of
the monitor.

The output of the monostable multivibrator is also buffered
by transistor A209. The emitter of A208 is direct coupled
to the base of A209. Diodes A2CR7 and 8 form the
emitter load so that the linearity of the multivibrator is
preserved. This type of coupling decreases the rise time of
the pulse output of A209 and enables transistor A2Q9 to
be driven between cut-off and saturation to form a
precisely defined rectangular pulse of maximum stability
for frequency measurements.

The output of transistor A2Q9 is integrated by the RC
network A2R50 and A2C27 to provide a DC that is
proportional to frequency. This DC is compared with the
reference DC from the precision voltage divider, A2R40
and A2R41, by the differential amplifier A2Q013—17. Any
difference in voltage then corresponds to a frequency
deviation and is amplified by the differential amplifier and
applied to the carrier deviation meter through pins 16 and
20. A2C26 couples the unfiltered modulation to the
reference input of the differential amplifier to prevent low

modulating frequencies from affecting the frequency
reading. The reference DC voltage is derived from the same
15 volt supply that powers the monostable multivibrator to
form a bridge circuit so that the frequency measurement is
relatively independent of supply voltage.

The 15 volt regulator is the series type to provide both
voltage regulation and a low impedance to power the A2
Card. A2Q18 is the pass transistor and A20Q19 and 20
amplify the error difference between the output and
reference zener diode, A2CR9. A2R52 sets the output to
15 volts.

The calibrating oscillator A2Q1 is a conventional Colpitts
crystal oscillator. When the FREQ CAL switch S2 is
depressed, 15 VDC from pin 7 is applied to pin 3 which
supplies power to the calibrating oscillator and also turns
on diode A2CR2 so that the 650 kHz calibrating signal is
applied to the limiter, A2Q2 and A203. Note that diode
A2CR1 is now turned off in this mode of operation. The
calibrating signal allows the pulse width of the monostable
multivibrator to be standardized to correspond with the DC
reference level of the differential amplifier.

Modulation calibration is accomplished by gating the 650
kHz calibrating signal on and off through the limiter. When
the MOD CAL switch S2 is depressed, the calibrating
oscillator is turned on as before. 19 volts, 60 Hertz is also
applied to pin 2 to gate the limiter stage A2Q3 on and off
at a 60 Hertz rate. The effective FM frequency deviation is
from 0 to 650 kHz or 650 kHz peak to peak; the 650 kHz
deviation is reduced to 150 kHz by the precision resistance
divider A2R38 and A2R39. The square wave output from
pin 13, through switch S2, is applied to the Amplifier Card
Assembly A3 and the Composite Output Jacks J1—4.
Capacitor A2C22 removes the overshoot from the leading
edge of the square wave.

25 VDC is supplied to pin 1 through R4, on the main
chassis, and to pin 11 to power the buffer A2010. R4
drops the 25 volts to pin 1 to approximately 21 volts to
reduce the power dissipated in the series regulator A2018.

4—2—3 AMPLIFIER, METERING
AND FLASHER CIRCUITS

The inputs to the monitoring amplifier, metering circuit,
and peak flasher circuit are individually calibrated. The
modulation metering circuit consists of a phase splitter to
allow either the positive or negative modulation polarity to
be selected, a feedback amplifier, a peak diode detector
circuit, and current amplifier to drive the modulation
meter. The baseband signal is applied to the phase splitter
A3Q1 to allow either the positive or negative modulation to
be selected by switch S4 [MOD POLARITY] on main
chassis. Potentiometer A3R5 adjusts the gain on the
negative polarity to exactly match the positive polarity.
The wideband feedback amplifier consists of three
transistors A3Q2, 3 and 4. Potentiometer A3R15 adjusts
the gain of the amplifier to that value required for
calibration. Diode rectifier A3CR1 rectifies the positive half
of the signal to charge the capacitor A3C7 to a DC level

corresponding to peak value of the signal. The charging
time constant is extremely short and is determined by the
low output impedance of the feedback amplifier, diode
resistance and A3C7. This short time constant allows the
modulation meter to accurately respond to complex

waveforms of multiplex signals as well as short duration ©

bursts of program material. Resistor A3R20 controls the
discharge time of A3C7.

Field-effect transistor A305 provides a high impedance to
the rectifier circuit and transistor A3Q6 provides the
current gain to drive the modulation meter. Note that pins
12, 13 and 14 are connected to the MOD METER ZERO
potentiometer, R8, on the main chassis to form a bridge
circuit. R8 balances the bridge for zero current with no
signal. With a signal, the voltage increases on the emitter of
transistor A3Q6 to inbalance the bridge and current flows
through resistors A3R24 and 25. A sample of the current
through A3R24 is applied to the internal modulation meter
M2 in series with A3R23; pins 10 and 11 connect to the
modulation meter via switches S6 and S7. Resistor A3R23
controls both the damping and the rise time of the
modulation meter. When a remote meter is used to read
modulation, a sample of the current through A3R25 is
applied to the remote meter. Pins 11 and 13 connect the
remote modulation meter via the REMOTE METER switch
S5. An external 6.2K ohm resistor must be used in series
with the remote meter for correct damping and rise time.
This resistance may include the line resistance.

The peak flasher circuit consists of an amplifier, phase
splitter, Schmitt voltage comparator and monostable
multivibrator. The baseband signal is applied to the low
gain amplifier A30.14 which is direct coupled to the phase
splitter A3Q13. Potentiometer A3R49 sets the span for the
PERCENT—MODULATION potentiometer R9 on the front
panel. The Schmitt comparator has a dual input, A30Q11
and 12 to accept both negative and positive modulations
respectively. The PERCENT—MODULATION
potentiometer RQ is connected to pins 15, 16, and 17 to set
the firing level of the comparator. Hence, each time the
modulation exceeds the pre—set level, the Schmitt
comparator fires and develops a pulse to trigger the
monostable multivibrator. The monostable multivibrator

A3Q7 and 8 produces a rectangular pulse of three seconds
duration which drives the lamp switch A309. The PEAK
MOD light DS2 is the collector load for transistor A3Q9.
The power for the light is supplied by rectifier CR1 and
capacitor C1. A remote PEAK MOD light is driven by the
same power supply and switch and may be connected to
terminals TB2—9 and 10.

The monitoring amplifier is a three stage feedback amplifier
to provide a low distortion signal for both aural monitoring
and audio tests. The baseband signal is applied to the input
stage A3018 which both amplifies the signal and sums the
feedback voltage in the emitter. Transistor A3Q17 provides
additional amplification to drive the output transistors
A3Q15 and 16. Since the output transistors are a
complementary pair, they operate in push-pull. Diodes
A3CR4 and 5 provide forward bias to allow the output
transistors to operate class AB.

Feedback is taken from the output and applied to the
emitter of the input stage through A3R57. When terminals
24 and 26 are connected to each other and terminals 23
and 27 are connected to each other, the feedback follows a
75 usecond pre-emphasis curve so that the resultant output
is de-emphasized according to a 75 usecond curve. A3C22
controls the gain and phase of the amplifier so that it is
unconditionally stable. The DE-EMPHASIS switch S3
makes the necessary connections. A3R51 provides the 600
ohm output impedance to drive an aural monitoring
amplifier and A3R52 provides the 10K ohm output
impedance for audio tests.

The main power supply consists of a full wave bridge
rectifier followed by a voltage regulator. Transistor Q1 is
the pass transistor and is driven by the current amplifier O2
which has its base referenced to zener diode CR6. Diode
CR7 provides short circuit protection along with R3. When
excessive current is drawn from the regulator, the voltage
drop across R3 along with the emitter-base voltages of Q1
and Q2 exceeds the voltage drop across CR7 and the
current is limited to a safe value to prevent damage to the
transistors. Diode CR1 and capacitor C1 provide power to
operate the PEAK MOD light.

SECTION 5
MAINTENANCE

5—1 INTRODUCTION

This section contains maintenance and service information
for the FMM—1 Frequency and Modulation Monitor.
Included are Performance Checks, Adjustments and
Calibration Procedures and Troubleshooting Techniques.

5—2 PERFORMANCE CHECKS

The FMM-—1 is self-checking to a degree. Before performing
the check procedure, release all push buttons [out
position] depressing or leaving depressed the AMP BAL
switch S2 and the MOD POL switch S4. No connections
should be made to the back terminals or connectors except
for the line cord to TB1.

5—2—1 POWER AND OVEN CHECK

With AC power connected to the FMM—1 and the power
switch off [released], the oven light DS1 should cycle on
and off approximately every 30 seconds after initial
warm-up. When on, heat is applied to the oven. Depressing
the POWER switch S1 turns the unit on, and power light
DS3 indicates that the power is on.

5—2—2 OSCILLATOR LEVEL CHECK

Depressing the OSC level switch S7 indicates the oscillator
level on the MODULATION meter M2. The reading of the
level should be greater than 100% and should be noted for
future reference.

5—2—3 FREQUENCY METER AMPLIFIER CHECK

Depress the AMP BAL switch S2 and adjust AMP BAL
potentiometer RZ maximum clockwise to maximum
counterclockwise; the FREQUENCY meter M1 pointer
should go off scale in the positive and negative direction
respectively. Return the pointer to zero for normal
operation.

5—2—4 FREO METER DISCRIMINATOR CHECK

Depress the FREQ CAL switch S2 and adjust the FREO
CAL potentiometer R6 maximum clockwise to maximum
counterclockwise; the FREQUENCY meter M1 pointer
should go off scale in the positive and negative direction
respectively. Return the pointer to zero for normal
operation.

5—2—5 MOD METER AMPLIFIER ZERO CHECK

Depress the AMP BAL switch S2 and adjust the MOD
ZERO potentiometer R8 maximum clockwise to maximum
counterclockwise; the MODULATION meter M2 pointer
should move in a positive and negative direction about zero.
Return the pointer to zero for normal operation.

5—2—6 MODULATION CALIBRATOR CHECK

Depress the MOD CAL switch S2. The MODULATION
meter M2 should read 100%. The FREQUENCY meter M1
may move off from zero to plus or minus a few hundred
cycles.

5—2—7 REMOTE METER SWITCH CHECK

Depress the MOD CAL switch S2. The MODULATION
meter M2 should read 100%. Adjust the FREQ CAL
potentiometer R6 to a reading of plus 1 kHz. Depress the
REMOTE METER switch S5. This MODULATION meter
M2 reading should decrease approximately 6% and the
FREQUENCY meter M1 should return to zero. Release the
REMOTE METER switch S5 and the meters should return
to the previous readings. Return the FREQ CAL
potentiometer R6 to normal as in step 5—2—4.

5—2—8 PERCENT MOD POTENTIOMETER CHECK

Depress the MOD CAL switch S2. Adjust the PERCENT
MODULATION potentiometer RY to just turn on the
PEAK MODULATION light DS2. The light should turn on
at 100%. The light will continue to flash on and off at a
rate of 3 seconds on to a fraction of a second off.

5—2—9 MODULATION POLARITY CHECK

Depress the MOD CAL switch S2. The MODULATION
meter M2 should read 100%. Release the MOD POL switch
S4 and the MODULATION meter should continue to read
100%.

5—2—10 CARRIER LEVEL CHECK

Turn RF level control R18 maximum counterclockwise.
Apply RF carrier to the RF INPUT connector J7 [40
milliwatts is more than sufficient to drive the monitor to
100% carrier level indication] . Depress RF switch S6 and
adjust RF level control R18 until the MODULATION
meter M2 reads 100%. If considerable range remains on
R18, the RF output from the transmitter should be
reduced by adjusting the coupling probe in the transmitter.

5—2—11 OPERATE CHECK

With the RF carrier applied as in step 11, depress the
OPERATE switch S2. The FREQUENCY meter M1 will
indicate the frequency deviation from the assigned channel
frequency. The MODULATION meter M2 will indicate the
presence of modulation. The PEAK MODULATION light
DS2 will indicate positive and negative modulation peaks
according to the setting of the PERCENT MODULATION
potentiometer. It may be noted that the MODULATION
meter M2 may not track at all times with the PEAK
MODULATION light while monitoring program material.

This is due to the assymetrical nature of certain types of
program material, i. e., the positive and negative peaks are
not equal in amplitude. Since the PEAK MODULATION
light circuitry automatically selects the higher of the two
polarities, it can register a peak opposite to the polarity to
which the MODULATION meter is set.

5—2—12 DE-EMPHASIS SWITCH CHECK

With a 15 kHz modulated signal applied to the monitor, the
monitor amplifier output may be monitored at the AUDIO
TEST jack J8. Depressing the DE-EMPHASIS switch S3 will
cause a 17 db decrease in output level, and releasing S3 will
return the amplifier to a flat response. Note that the 600
ohm monitoring amplifier output on TB2 is also
de-emphasized by this switch.

5—3 ADJUSTMENTS, CALIBRATION
AND TROUBLESHOOTING

The following guide for adjustments, calibration and
troubleshooting follows the same numbering sequence as
the PERFORMANCE CHECKS for ease of service.

5—3—1 POWER AND OVEN

a. If the oven light DS1 fails to light, check fuse F2
[0.25A].

b. If the oven light DS1 lights but fails to cycle on and off,
remove oven from unit. If the oven is cold, check
continuity of the heater winding between pins 3 and 4 of
the oven. If the oven is hot, the thermostat circuit is stuck
closed and the oven should be replaced with a new unit.
Note that both malfunctions will result in an indicated
carrier frequency error. The monitor oven should not be
operated with a stuck thermostat as the crystal may be
damaged from overheating. The monitor may be operated
temporarily with the oven fuse removed.

c. If the oven light DS1 fails to light but the oven heats,
check the oven light.

d. If the power light DS3 fails to light, check fuse F1
[0.5A].

e. If the power light DS3 lights but the monitor is
inoperative, check the voltage on terminal 3 of TB2 to
ground. Normal voltage is 26 VDC. If the voltage is high
[37 VDC] , O2 or CRG is defective. If the voltage is 0, Q1 is
open or a malfunction exists in the pre-regulator.

f. If the power light DS3 fails to light and the monitor
functions normally, check the power light.

5—3—2 OSCILLATOR LEVEL

a. If the oscillator level reads O, transistor A1Q1 is
malfunctioning.

b. If the oscillator level reads above 80% but not the
normal peak, adjust A1L1 for an indicated peak on M2.

c. If the oscillator level will not peak with the adjustment
of A1L1, the crystal Y1 [in oven] may be defective.

5—3—3 FREQUENCY METER AMPLIFIER

a. If the FREQUENCY meter M1 pointer fails to go off
scale in both the positive and negative direction, transistors
A2Q14 and 15 are saturated and A2R47 should be replaced
with the next higher value [9.1K or 10K ohms].

b. If the FREQUENCY meter M1 pointer fails to move and
the rest of the monitor functions normally, release
REMOTE METER switch S5. Note that if remote meters
are used and the malfunction is cleared when the switch S5
is released, a malfunction exists on the remote meter lines.

c. If releasing the REMOTE METER switch S5 does not
clear the malfunction, A2013 and 17 are malfunctioning.

5—3—4 FREQ METER DISCRIMINATOR

a. If the FREQUENCY meter M1 pointer fails to go off
scale in both the positive and negative directions, return the
FREQ CAL potentiometer R6 to its midpoint and adjust
the coarse frequency potentiometer R5 to zero M1.

b. If the FREQUENCY meter M1 is off scale and cannot
be brought on scale with R6, as in step (a) above, but the
modulation calibrator functions normally as in step 5—2—6,
check the waveform on the collector of transistor A2Q9. A
low capacity probe should be used with the oscilloscope to
preserve the waveshape and the waveshape should be as
shown in Figure 4—2—3. If the waveshape does not have a
straight base-line as in Figure 4—2—10, transistor A2Q9 is
not driven into full saturation and should be replaced. Note
that this malfunction can also cause excessive frequency
drift in the discriminator.

c. If the FREQUENCY meter M1 is off scale and the
modulation calibrator does not check as in step 5—2—6, but
the unit functions normally in the OPERATE position, the
calibrating oscillator is not functioning or the diode switch
A2CR2 is open. Check also that 15 VDC is applied to the
diode anode.

d. If the unit does not function in the OPERATE position
in step (c) above, the counter-discriminator circuits are
malfunctioning, and the signal may be traced with the aid
of the waveforms in Figure 4—2. A low capacity probe
should be used with the oscilloscope to preserve the
waveshape.

5—3—5 MOD METER AMPLIFIER ZERO

a. If the MODULATION meter M2 will not zero, and the
modulation calibrator functions but does not indicate
accurately, the bias on transistor A3Q3 is off. Increasing
the value of A3R16 will decrease the meter reading by
shifting the zero to the negative direction, and decreasing
A3R16 will increase the meter reading by shifting the zero
to the positive direction. A3R16 should range between 24K
and 30K ohms and if it does not, replace A3Q5 or A303.

b. If the MODULATION meter M2 reads off scale, check
resistors A3R 24 and 25 for an open circuit.

5—3—6 MODULATION CALIBRATOR

a. If the MODULATION meter M2 reads in error but is
within 20% for positive polarity [MOD POL switch S4
depressed] and the PERCENT MOD checks as in step
5—2-—8, adjust potentiometer A3R15 for the correct
reading of 100% after zeroing the meter as in step 5—2—5.

b. If both the MODULATION meter M2 and the
PERCENT MOD potentiometer RQ read in error, check the
voltage output of the 15 volt regulator on card A2 and
adjust A2R52 for 15 volts output if necessary. Usually the
FREQ METER DISCRIMINATOR CHECK will be off in
step 5—2—4 with the 15 volt regulator out of adjustment.

5—3—7 REMOTE METER SWITCH

a. With remote meters connected to the monitor, the
readings of the FREQUENCY meter M1 and the
MODULATION meter M2 should remain unchanged with
the REMOTE METER switch S5 depressed or released. If
the readings do change, check for faults on the remote
meter lines. When the remote meters are not connected to
the monitor, the readings will change as in step 5—2—7.

5—3—8 PERCENT MOD POTENTIOMETER

a. If the PERCENT MOD potentiometer R9 reads in error,
the knob may be slipped to the correct reading by
loosening the two set screws and retightening after
adjusting.

b. The span of the PERCENT MOD potentiometer may be
checked by applying a 400 cycle modulated signal to the
monitor and checking the tracking at the 50% and 100%
modulation points. Adjust A3R49 so that the percentage
difference on the PERCENT MOD potentiometer is 50%
when the modulation level is changed from 100% to 50%.
Slip the knob as in step (a) above if it is necessary to
correct the reading at 100% after the span has been
adjusted.

5—3—9 MODULATION POLARITY

a. With a 400 cycle, 100% modulated signal, adjust A3R5
‘to obtain equal reading on MODULATION meter M2 when

the MOD POL switch S4 is cycled from positive to negative.
Note that the adjustment can be observed in the negative
polarity position.

b. If the negative polarity if off seriously and the monitor
is noisy, check the pre-regulated power supply as in step
5—3—1-e.

5—3—10 CARRIER LEVEL

a. If no RF level is observed and the monitor is functioning
normally in the OPERATE position, check diode A1CR3.

5—3—11 OPERATE

a. If the monitor fails to function in the OPERATE
position and all other functions are. correct, check diode
switch A2CR1. Check also that 15 VDC is applied to the
diode anode.

b. If the FREQUENCY deviation is off scale and the
MODULATION meter is normal in the OPERATE position,
check local oscillator peaking as in step 5—3—2.

c. If the FREQUENCY deviation is off scale and the
MODULATION meter is normal in the OPERATE position,
check the oven cycling as in step 5—3—1—b. If the oven is
cycling and the transmitter frequency is correct, crystal Y1
[in oven] is defective.

d. If the monitor fails to function in the OPERATE
position and the diode switch circuit is functioning, check
transistors A102 and A1Q3.

5—3—12 DE-EMPHASIS SWITCH

a. If DE-EMPHASIS switch S3 does not function normally,
check capacitors A3C20 and 22. In the DE-EMPHASIS
position, capacitor A3C20 is connected to the circuit by S3
switch contacts connecting pins 24 and 26, and capacitor
A3C22 is connected to the circuit by S3 switch contacts
connecting pins 23 and 27.

Figure 5—1

200 VDCW
| 2.0 MFD

Figure 5—2

REF GRID
LOC

ON OOBBWDN

Figure 5—3

1
2
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4
5
6
7
8

PLIITIE DU ROR RC ar carrie

Figure 5—4

ve aa

Figure 5—5

SECTION 6
REPLACEABLE PARTS

6—1 INTRODUCTION

including the reference

This section contains information for ordering information:

replaceable parts for the monitor. The table lists the

parts in alpha-numerical order of their reference a. Model number and serial number of unit.
designations and provides a description of the part

with the manufacturers’ number and the Belar part. b. Description of part

number. Those parts with only a Belar part number designation and location.

should be obtained directly from Belar.

c. Belar part number.

6—2 ORDERING INFORMATION

To order a part from a manufacturer other than Belar,
To order a replacement part from Belar, address the provide the complete part description and the
order or inquiry to Belar and supply the following manufacturer’s part number from the table.

REFERENCE DESIGNATORS

A = assembly al = jack

& = capacitor L = inductor

CR = diode M = meter

DS = device signaling(lamp) P = plug

F = fuse ‘@) = transistor

FL = filter R = resistor

ABBREVIATIONS

SCER = ceramic MEG = meg

COMP = composition METFLM = metal film
CONN = connector MY = mylar

ELEGT, = electrolytic EG = printed circuits
F = farads PIV = peak inverse voltage
FXD = fixed POLY = polystyrene
GE “= germanium PORC = porcelain

K = kilo = 1000

4A”
<xeq

POT
SEMICON
Sl

VDCW

WwW

= switch

transistor
terminal board
cable

oven

= crystal

potentiometer
semiconductor
silicon

micro

de working volts
watts

wirewound

PARTS LIST
MAIN CHASSIS
REFERENCE DESCRIPTION PART NUMBER
DESIGNATION
C1 C: FXD ELECT 500 UF 50 VDC SPRAGUE TVL1330 0180-0001
C2 C: FXD ELECT 1000 UF 50 VDC SPRAGUE TVL1338 0180-0002
C3 C: FXD ELECT 1000 UF 50 VDC SPRAGUE TVL1338 0180-0002
C4 C: FXD CER 15 PF 2% CENTRALAB TCZ 0150-0001
C5 C: VAR AIR 3.2—50 PF JOHNSON 148-4 0121-0001
C6 C: FXD FLM .0047 UF 10% 80 VDC SPRAGUE 192P 0120-0001
C7 C: FXD CER .01 UF 1 KV AUTOMATIC COMP 0150-0003
C8 C: FXD MICA 250 PF 5% 500 VDC ELMENCO DM15 0140-0001
C9 thru C11 C: FXD CER .01 UF 1 KV AUTOMATIC COMP 0150-0003
C12 thru C22 C: FXD CER .001 UF 1 KV SPRAGUE X5E 0150-0004
CR1 thru CR5 DIODE: SILICON 1N2070 1900-0003
CR6 DIODE: ZENER 1N3030B 1900-0004
CR7 DIODE:BELAR 1900-0010
DS1 LAMP: INDICATOR ASSEMBLY RED DIALCO 1450-0002
DS2 LAMP: INCANDESCENT 28V 0.07A GE1829 2140-0001
DS3 LAMP: INDICATOR ASSEMBLY AMBER DIALCO 1450-0003
Rt FUSE: CARTRIDGE %A 250V LITTLEFUSE 3AG - 2A 2110-0001
F2 FUSE: CARTRIDGE %A 250V LITTLEFUSE 3AG -%A 2110-0002
M1 FREQUENCY METER:+3 kHz 1120-0001
M2 MODULATION METER: 0 TO 133% MOD 1120-0002
Q1 TRANSISTOR: SILICON 2N3054 1850-0009
Q2 TRANSISTOR: SILICON 2N3053 1850-0008
R1 R: FXD WW 1.5 OHM 5% 3W SPRAGUE 242E 0811-0001
R2 R: FXD COMP 1K OHM 5% %W RC20GF 0686-1025
R3 R: FXD WW 0.33 OHM 5% 1W IRC-BWH 0811-0002
R4 R: FXD WW 33 OHM 5% 3W SPRAGUE 242E 0811-0003
R5 R: VAR WW 500 OHM 10% 2W RA20NASD 501A 2100-0001
R6 R: VAR WW 50 OHM 10% 2W RA20NASD 500A 2100-0002
R7 R: VAR WW 100 OHM 10% 2W RA20NASD 101A 2100-0003
R8 R: VAR WW 100 OHM 10% 2W RA20NASD 101A 2100-0003
RQ R: VAR WW 500 OHM 10% 2W RA20NASD 501A 2100-0001
R10 R: FXD COMP 6.2K OHM 5% ZW RC20GF 0686-6225
R11 R: FXD COMP 5.1K OHM 5% %W RC20GF 0686-5125
R12 thru R14 R: FXD COMP 2.2K OHM 5% “%W RC20GF 0686-2225
R15 R:FXD COMP 560 OHM 5% %W RC20GF 0686-5615
R16 R: FXD COMP 15K OHM 5% “ZW RC20GF 0686-1535
R17 R: FXD COMP 100 OHM 10% 1W RC32GF 0690-1011
R18 R: VAR COMP 100 OHM 10% 2W RV4LAYSA101A 2100-0010
R19 R: FXD COMP 1K OHM 5% %W RC20GF 0686-1025
R20,R21 R: FXD COMP 200 OHM 5% “ZW RC20GF 0686-2015
R22 R: FXD COMP 47K OHM 5% “W RC20GF 0686-4735
R23 R: FXD WW 100 OHM 5% 3W SPRAGUE 242E 0811-0004
$1,S5,56,57 S: PUSH BUTTON POWER—METER 3101-0001
$2 S: PUSH BUTTON FUNCTION 3101-0002
$3,S4 S: PUSH BUTTON DE-EMPHASIS—POLARITY 3101-0003
T1 TRANSFORMER: POWER 9100-0001
TB1 TERMINAL BLOCK: 3 PT 0360-0001
TB2 TERMINAL BLOCK: 12 PT 0360-0002
X11 OVEN: CRYSTAL 117V 75 DEGREES CENTIGRADE 0410-0001
wit CRYSTAL: FREQUENCY 29-36 MHz 0410-0002
A1 CARD, OSCILLATOR, TRIPLER AND MIXER
A1C1A C: FXD CER 22 PF 2% NPO CENTRALAB TCZ 0150-0005

A1C1B C: FXD CER 5PF 2% N750 CENTRALAB TCN 0150-0006

REFERENCE
DESIGNATION

DESCRIPTION PART NUMBER

A1C2
A1C3
A1C4
A1C5
A1C6
A1C7
A1C8
A1C9
A1C10
AiC11
A1C12
A1C13
A1C14
A1C15
A1C16
A1C17

A1CR1,CR2

A1CR3
A1L1
A1L2
A1Q1,02
A1Q3
A1R1
A1R2
A1R3
A1R4
A1R5
A1R6
A1R7
A1R8
A1R9
A1R10
A1R11
A1R12
A1R13
A1R14
A1RFC1

A1RFC2 thru RFC4

A1RFC5

A2 CARD, OSCILLATOR, COUNTER DISCRIMINATOR

: FXD MICA 12 PF 5% 500 VDC ELMENCO DM15

: VAR CER 5.5—18 PF ERIE 538-011 COPO 92R