Belar AMM-2B User manual

Model AMM-2B
AM MODULATION
MONITOR
Guide to Operations
BELAR ELECTRONICS LABORATORV, INC.
119 LANCASTER AVENUE
P.O. BOX 76
DEVON, PA 19333-0076 USA
[phone] • FAX [phone]

1 General Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1-1 General Description ................................... 1
1-2 Physical Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1-3 Electrical Description
.................................. 1
1-4 Electrical Specifications
................................ 2
1-5 Mechanical Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1-6 Instrument Identification
................................ 3
1-7
Accessories......................................... 3
2 Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2-1 Initial Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 4
2-2
Claims............................................ 4
2-3 Repacking for Shipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.. 4
2-4 Preparation for Use
................................... 4
3
Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3-1 Initial Operation ..................... . . . . . . . . . . . . . . . . . 7
3-2 Normal Operation
.................................... 8
3-3 Transmitter Measurements
.............................. 8
3-4 NRSC De-emphasis Modification. . . . . . . . . . . . . . . . . . . . . . . . .. 8
4 Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.. 10
4-1 Test Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 10
4-2 Modulation Meter Alignment Procedure ..................... 10
4-3 Peak Indicator Alignment Procedure ....................... 11
5 Diagrams, Schematics and Parts Lists . . . . . . . . . . . . . . . . . . . . . . . . . .. 12
BELAR ELECTRONICS LABORATORY, INC.

Important Note about the Belar AMM-2B, the Belar AMM-
2A, and the Belar AMM-2:
This instruction manual covers models AMM-2B, AMM-2A and AMM-2.
The model AMM-2B
is identical to the model AMM-2A except for front-panel
cosmetics.
Below are the components used
in the AMM-2 which differ from the
AMM-2B:
A1 CARD
R40 R: METAL FILM 10.0kO 1%
R43 R: FIXED CARBON 10MO 5% V4W
R47 R: METAL FILM 6.19kO 1%
R61 R: METAL FILM 5.11kO 1%
U7 IC: NE536T
U8
IC: MC1741SCP1
CHASSIS
DS1 & DS2
M1
M2
T1
NOT USED
METER: CARRIER LEVEL 1120-0013
METER: MODULATION 1120-0012
TRANSFORMER: POWER CTC 3143
BELAR ELECTRONICS U-.BORATORY, INC.

1 General Information
1-1 General Description
The Belar AMM-2B AM Modulation Monitor (FCC Type Approval #3-240), is an all
solid state precision AM demodulator designed to meet the Federal Communications
Commission requirements for measuring the total modulation characteristics of
AM
broadcast transmitters. Since the input circuitry is non-frequency discriminating, the
AMM-2B is also suitable for measuring the modulation characteristics of shortwave
transmitters as well
as VHF transmitters. A switch is provided to measure either positive
or negative polarities on the modulation meter and the adjustable peak indicator.
Separate peak indicators are provided to indicate negative peaks
in excess of 99% and
positive peaks
in excess of 125%. The AMM-2B incorporates a carrier-off alarm and a
modulation calibrator to insure the accuracy of the readings at any time.
1-2 Physical Description
The AMM-2B is constructed on a standard EIA 5114 x 19-inch rack mount.
Calibration adjustments are located within the unit and are accessible through the back
cover. The AC power input, RF input, and monitor outputs are located at the rear of the
AMM-2B chassis on individual connectors and rear terminal block. The AMM-2B is
completely solid state, utilizing all silicon transistors and integrated circuits for long,
trouble-free life. LEOs (light-emitting diodes) are used for the indicators to eliminate lamp
burn-out. The individual circuits are constructed on a military-grade, glass-epoxy, plated,
printed circuit board. High-reliability military and industrial grade components are used
throughout.
1-3 Electrical Description
The AMM-2B is a solid state, low-sensitivity, precIsion AM demodulator
incorporating a highly linear, biased diode detector. The detector circuit will accurately
demodulate
AM envelopes of carriers from 200 kHz to 160 MHz. Various metering and
testing provisions are contained within the monitor to measure transmitter output
characteristics. These provisions include a zero center carrier level deviation meter; a
peak-reading modulation meter, switchable to either positive or negative modulation
polarity; a peak modulation light, adjustable from
40 to 130% peak modulation and
switched with the modulation meter to either positive or negative modulation polarity; a
peak modulation light that responds when the negative modulation exceeds 99%; a peak
modulation light that responds when the positive modulation exceeds 125%; a DC-type
modulation calibrator to check the ratio between the carrier level and peak modulation
reading; a carrier-off light that responds when the carrier
is less than 70% of nominal
value (this may be set to other values by the change of a resistor value). Outputs
obtained from the monitor include
an output for aural monitoring, a distortion meter test
BELAR ELECTRONICS LABORATORY, INC. 1

output, a transistor driver for carrier-off alarm, and a transistor driver for remoting each
of the three peak lights. FCC type-approved remote metering of the AMM-2B may be
externally provided for the carrier level deviation meter and modulation meter.
1-4 Electrical Specifications
RF Frequency Range ................................ 200 kHz to 160 MHz
RF Sensitivity ...................................... 5 to 10 Volts RMS
RF Input Impedance .................................. 1000 Q standard
50 Q optional
Modulation Meter Range
.................................... 0 to 133%
(switchable to either positive or negative peaks)
Carrier Level Meter Range
........... . . . . . . . . . . . . . . . . . . . . . . . . . .. ±30%
Modulation Meter Accuracy ........................ 2% at 100% modulation
Peak Modulation Indicator* ........................ 40 to 130% in less than
(switchable to either positive
1% increments or negative peaks)
Peak Modulation Indicator Accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2%
100% Negative Indicator* . . . . . . . . . . . . . . . . . . . . . . . . . .. Adjustable 85 to 100%
125% Positive Indicator* .......................... Adjustable 100 to 130%
Carrier Off Alarm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fixed to alarm with a 30%
drop in carrier level
Frequency Response
............................ 0.5 dB from 20-25,000 Hz
Pulse Response ................................ Overshoot less than 1%
Distortion
............................... 0.25% max. at 99% modulation
Signal to Noise Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 75 dB
Remote Metering . . . . . . . . . . . . . . . . . . . . . . .
.. Meters may be remotely metered
5000 Q external loop resistance
Aural Monitoring
Output. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. + 10 dBm, 600 Q
Aural Proof of Performance Output . . . . . . . . . . . . . . . . . . . . . . . . . .. 5 Volts RMS
Power Consumption ....................... 8 watts, 115/230V, 50 to 400 Hz
Operating Temperature .................................. 0°C to +50°C
*
2
Peak modulation, 100% negative and 125% positive indicators are true ratio types
and will hold their accuracies over a ± 30% input carrier level change.
Model AMM-2B
AM Modulation Monitor

1-5 Mechanical Specifications
Dimensions
...................................... 5114" H X 8" D X 19" W
(133 x 216 x 483 mm)
(EtA Rack Mount)
Net Weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 pounds (3.6kg)
Shipping Weight
.................................... 12 pounds (5.4kg)
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.
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 AMM-2B Modulation Monitor may be used for remote monitoring of an
AM transmitter with either the Belar MP-6B Remote Meter panel or the Belar RFA-2 AM
RF Amplifier. The MP-6B Remote Meter panel contains a carrier level deviation meter,
modulation meter and 3 peak lights.
In cases where complete duplication of the AMM-2B front panel indications is not
required, or where interconnection wiring precludes the use of the MP-6B Remote meter
panel, an unmounted modulation meter may be ordered from Belar. This meter is
identical to the unit incorporated in the monitor and meets the FCC ballistics requirement.
The Belar RFA-2
AM RF amplifier provides preamplification and selectivity to permit
direct off-air monitoring with the AMM-2B.
BELAR ELECTRONICS LABORATORY, INC. 3

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.
The AMM-2B is shipped with an instruction book, three wire line cord, and four
beige rack mount screws.
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 to 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 AMM-2B AM 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. When the monitor is mounted above high-heat generating
4 Model AMM-2B
AM Modulation Monitor

equipment such as power supplies and amplifiers, consideration should be given to
cooling requirements which allow a
free movement of cooler air around the AMM-2B. In
no instance should the ambient chassis temperature be allowed to rise above 50°C
(122°F). Mount the AMM-2B to the rack using the four rack-mount screws provided.
The Model AMM-2B can be operated from either a 105 to 125 Vac or 210 to
250
Vac single phase, 50 to 400 Hz power source. Make sure the unit is set for the proper
voltage as follows:
Units with serial number 133536 and lower:
Unplug the line cord. Slide the switch (S1) to 115V or 230V position.
Ensure that the fuse
(F1) is the proper current rating for selected voltage
(V2A 250V for 115Vac, V4A 250V for 230Vac). Plug the line cord back in.
Units with serial number 133537 and higher:
Unplug the line cord. Open the fuse compartment door and pull lever to
remove fuse. Using needlenose pliers, pull the voltage select board straight
out of the power entry module. While facing the rear of the unit, orient the
voltage select board so the desired line voltage is face up and reads
correctly ("120" for 115Vac operation, "240" for 230Vac operation. The "100"
and "220" positions on the bottom of the board are not used.) Reinsert the
board into the power entry module, install the proper fuse (V2A 250V for
115Vac,
V4A 250V for 230Vac), close the fuse door, and plug the line cord
back in.
The Model AMM-2B is supplied with a three-conductor power cable which, when
plugged into an appropriate receptacle, grounds the unit. The offset pin on the power
cable three-prong connector
is the ground wire. To preserve the grounding feature when
operating the unit from a two-contact outlet, use a three-prong to two-prong adaptor and
connect the green pigtail on the adaptor to ground. Attach the power cable between the
unit and the power source receptacle.
CAUTION: DO NOT APPLY MORE THAN 15 VOLTS RF TO
THE MONITOR OR THE RF INPUT CIRCUIT MAY BE
DAMAGED! BEFORE APPLYING ANY RF INPUT, TURN
CARRIER LEVEL CONTROL MAXIMUM
COUNTERCLOCKWISE!
Damage as a result of excessive RF input is not covered under the warranty.
BELAR ELECTRONICS LABORATORY, INC. 5

Connect a coaxial cable between the monitoring probe on the transmitter (or RF
Amplifier) and the RF INPUT connector J2 at the rear of main chassis.
A remote carrier level deviation meter and one remote modulation meter can
be
connected to terminals on TB1 on the rear panel of the AMM-2B. The remote metering
circuits are activated when the REMote button is depressed. The equivalent series
resistances of both external metering circuits must
be equal to values of internal circuit
resistances for proper operation of the monitor in the REMote mode. The required
external resistances are
5.1 kO for the carrier level deviation circuit and 7.5 kO for the
modulation meter circuit. If the total series resistance of the external loop and meter is
less than the required value, resistors must be added to the line to obtain the required
value. If one external metering circuit
is not used, a resistor of the required value must
be connected to TB 1 in place of the external loop. When remoting meters via DC
telephone pairs, it is advisable to split the added resistance equally between the two legs
of the external loop and to place the added resistors at the monitor end. This helps
balance the line and provides additional protection for the monitor from line transients,
such as lightning.
The remote carrier level deviation meter (or substitute resistance) should be
connected between terminals 9 and 10 of TB1. The remote modulation meter (or
substitute resistance) should
be connected between terminals 8 and 12. Proper meter
polarity must be observed. Terminals 8 and 9 are positive.
As an example, if only a remote modulation meter is used, the remote modulation
metering circuit, with series resistance adjusted to 7.5 kO, is connected to terminals 8 and
12. In order for the carrier level deviation meter to function properly with the REM button
depressed, a 5.1 kO resistor must be connected between terminals 9 and 10.
The external loop resistances may be conveniently adjusted by putting the monitor
in the CAlibrate with a steady, unmodulated carrier. The external loop resistance for the
modulation circuit is correct when depressing the REM button causes no change in the
reading ofthe internal modulation meter. This technique may be used for the carrier level
circuit, but since the carrier level deviation meter has a center zero, the carrier level
should first be adjusted to either end of the meter scale using the CARRIER SET control.
Any change in indicated carrier level deviation on the internal meter when the REM button
is pushed indicated an incorrect external loop resistance.
Remote modulation meters should
be obtained from Belar so that FCC meter
ballistics are met.
Remote peak modulation lamps and a carrier level alarm may also be driven from
terminals on TB-1. The peak lamp and carrier
level alarm outputs are open transistor
6 Model AMM-2B
AM Modulation Monitor

collectors that are pulled to ground when the respective LEOs are lit. Terminal 1 of TB1
is a 5-volt source which is available to drive external lamps. If LED's are used as external
indicators, a series resistor must
be used to limit the current in each diode to an
appropriate value. As an example, a remote peak modulation lamp would be connected
between terminals 1 and 3 on
TB 1.
If a relay is used for any of the indicator outputs, it must be a sensitive (low
current) type and the output transistor must be protected from the back EMF of the coil
by a diode or other means.
3 Operation
3-1 Initial Operation
1. Before turning the unit on, ensure that the unit has been configured to operate with
the line voltage you will be using
(see Section 2-4 Preparation for Use).
2. Depress the ZERO switch and release the REMOTE switch. Turn CARRIER SET
control maximum counterclockwise.
3. Depress POWER switch. Note that the % CARRIER LEVEL DEVIATION meter is
pegged to the left, the
CARRIER OFF alarm light is on, and the MODULATION
meter is approximately zero. Allow a few minutes warm-up.
4. After warm-up, the MODULATION meter will read zero. If it does not read zero but
is only off a few percentage points, it may be set to read zero with the mechanical
zero control on the meter. If the zero
is off more than a few percentage points, the
zero should be set according to Section 4-2 Modulation Meter Alignment
Procedure. The electrical zero
is stabilized by a feed-back operational amplifier
and normally does not need re-adjustment.
5. Rotate the CARRIER SET control clockwise. The CARRIER OFF light will go out
at approximately minus 30% carrier level deviation. Continue to rotate the control
so that the CARRIER LEVEL DEVIATION meter reads zero. Note that this
is the
carrier level SET point.
6. Depress the CAL switch. The MODULATION meter will read 100% to verify the
accuracy
of the calibration. The + 125% light will be on. (The -100% light will not
be on
in the calibrate mode.)
7. Adjust the PEAK MOD potentiometer to the point where the PEAK MOD light just
turns on. This setting will
be 100%.
BELAR ELECTRONICS LABORATORY, INC.
7

8. Depress the POS or NEG switch for positive or negative modulation reading on the
MODULATION meter and PEAK MOD light, and the monitor is ready for operation.
3-2 Normal Operation
For normal operation, leave the AMM-2B in POS position when broadcasting
super-modulation. The MODULATION meter and
PEAK MOD light will register the positive
peaks. Nominal changes
in RF level wi" not affect the accuracy of the -100%, +125%,
or PEAK MOD lights.
The PEAK MOD control
is usually set to a level slightly lower than +125%, say
+120%, and the separate -100% and the +125% lights are used for the limits to insure
the maximum level of modulation without exceeding the limits set by the
FCC.
Percent carrier shift is read on the % CARRIER LEVEL DEVIATION meter as a
change
in carrier intensity during modulation.
3-3 Transmitter Measurements
Normal transmitter proof-of-performance measurements may be made with the
AMM-2B. Frequency response, distortion, and noise measurements may be made
through the rear panel AUDIO TEST jack
J3. Five volts RMS is available at 100%
modulation so that most distortion and noise analyzers may be used. Percent modulation
is read on the MODULATION meter and percent carrier shift is read on the % CARRIER
LEVEL DEVIATION meter.
3-4 NRSC De-emphasis Modification
This modification de-emphasizes the demodulated audio output of the Belar
AMM-2A or AMM-2B
AM Modulation Monitor. With the modification installed, the
monitor's audio output frequency response closely approximates the interim NRSC
de-emphasis characteristic.
This change affects the audio present at the AUDIO TEST output (J3), the AURAL
MONITOR OUTPUT (TB1, screw 11) and the AUX DET OUTPUT (TB1, screw 6).
Parts required:
Quantity
1
1
1
8
Description
14.7kQ 1% metal film resistor
4.64kQ 1% metal film resistor
3900pF 2.5% 160V poly capacitor
Belar Part No.
0721-1472
0721-4641
0130-3922
Model AMM-2B AM Modulation Monitor

Procedure:
Remove
the existing R53 (15kQ carbon resistor) from the A1 board by cutting the
leads as close
to the resistor body as possible. (See accompanying component layout
sheet for R53 location).
Preform the modification parts by connecting the 4.64kQ resistor
and 3900pF
capacitor in series and then connecting these two across the 14.7kQ resistor as shown
on the modification schematic. Use short leads and
be careful not to use excessive heat
when soldering the parts together.
Mechanically connect the modification network to the original R53 leads on the A1
board. Solder the network
to these leads using as little heat as possible so the leads do
not pull out of the board. This completes the modification.
BELAR ELECTRONICS LABORATORY, INC. 9

4 Maintenance
4-1 Test Equipment
1. Voltmeter
2. High Frequency oscilloscope with 5" display
3. Linear modulator, output level of 5-10 volts RMS unmodulated*
4. Low distortion oscillator
4-2 Modulation Meter Alignment Procedure
1. Turn power off and set mechanical zero on meters.
2. Turn power on and allow to warm up for 15 minutes.
3. With Voltmeter measure voltage at U5 Pin 7. Voltage should be +15 Volts, ±0.5
volt. Adjust R30 for correct reading.
4. With Voltmeter measure voltage at U5 Pin 4. Voltage should be -15 volts, ±0.5
volt. Adjust R25 for correct reading.
5. Place Function Switch in ZERO position and Voltmeter at Pin 6 U5 and adjust R37
for Zero Volts.
6. Adjust R44 for Zero on Modulation Meter.
7. Apply an RF level of 5-10 volts to RF input, and adjust CARRIER SET to -0-
deviation on Carrier Meter. Connect Oscilloscope at RF INPUT (J2) of monitor.
8. Apply a 1 kHz tone to modulator and adjust level for just 100% negative
modulation as observed on oscilloscope. Depress NEG on Function Switch of
AMM-2B. Monitor should indicate 100% modulation.
If not, adjust METER AMP,
R41, for correct reading.*
9. Reduce modulation level to 90% on AMM-2B. Place Function Switch in POS
position. Monitor should indicate 90% modulation. If not, adjust NEG AMP, R36,
for correct reading.*
10. Place Function Switch in CAL position. Monitor should indicate 100%. If not,
adjust CAL ADJ,
R14, for correct reading.
10 Model AMM-2B AM Modulation Monitor

4-3 Peak Indicator Alignment Procedure
1. CARRIER OFF INDICATOR: Reduce CARRIER SET Potentiometerto -30% or less
on CARRIER LEVEL Meter. CARRIER OFF Indicator should be on. This
is a fixed
comparator and no adjustment
is provided.
2. -100% PEAK INDICATOR: Adjust CARRIER SET to -0- Deviation on CARRIER
LEVEL Meter. Adjust modulation for 98% or greater. The -100% Indicator should
be on. If not, adjust -100%
R69, for correct indication.
3. PEAK MOD INDICATOR:
a) Place Function Switch in POS position. Adjust modulation level for 90% on
AMM-2B. Adjust
PEAK MOD Potentiometer on front for 90%*. If the PEAK MOD
potentiometer R1 reads in error, the knob may be slipped to correct reading by
loosening the two set screws and retightening after adjusting.
b) The span of the PEAK
MOD Potentiometer may be checked by applying a 1
kHz tone to the Modulator and adjusting the modulation to 90% on the AMM-2B.
Adjust PEAK MOD Span Potentiometer, R60, so that the percentage difference on
the PEAK MOD Potentiometer on the front panel is 50% when the modulation level
is changed from 90% to
40%. Slip the knob as in step (a) above if it is necessary
to correct the reading
at 90% after the span has been adjusted.
4. + 125% PEAK INDICATOR: Place Function Switch in CAL position. The +125%
Indicator should
be on. If not, adjust +125%, R65, for correct indication.
* Note that the modulation meter and peak lights respond to peak values of
modulation so that
if there is distortion in the modulator, the peak indications will
be the true peak values,
Le., the sum of fundamental and the harmonics or
distortion products. The most common mistake made
in calibrating AM monitors
is to adjust the modulation level until carrier shut-off
is reached. This is defined as
100% negative and, indeed, it is 100% negative, but the positive value is not
necessarily 100%.
If the distortion is 3% at this level (typical of many transmitters),
the positive value of modulation may be anywhere from 97% to 103%, depending
on the phase of the harmonics, and the monitor will read this. It
is for this reason
that we suggest the monitor
be calibrated at just 100% negative on the negative
indications and then to back off the modulation to 90% for the positive indications
so they can be set
in the region where the transmitter is more linear.
BELAR ELECTRONICS LABORATORY, INC.
11

5 Diagrams, Schematics and Parts Lists
Replaceable Parts. This page contains information for ordering replaceable parts
for the monitor. The tables that follow list the parts
in alphanumeric order by reference
designation and provides a description of the part with the Belar part number.
Ordering Information. To order a replacement part from Belar, address the order or
inquiry to Belar and supply the following information:
a. Model number and serial number of unit.
b. Description of part, including the reference designation and location.
Orders may also be taken over the telephone. Parts orders can be put on your VISA,
MasterCard, or American Express card, or we can ship them COD.
REFERENCE DESIGNATORS
A = assembly
BA = diode bridge
C = capacitor
CA = diode or LED
OS = display or lamp
F = fuse
FL = filter
HDA = header connector
ABBREVIATIONS
12
BCD
CEA
COMP
CONN
DPM
ELEC
GE
IC
k
M
MOD
MY
PC
pF
= binary coded decimal
= ceramic
= composition
= connector
= digital panel meter
= electrolytic
= germanium
= integrated circuit
= kilo = 1,000
= meg = 1,000,000
= modulation
= mylar
= printed circuit
= picofarads
J
L
M
P
0
A
AL
AN
= jack
= inductor
= meter
= plug
= transistor
= resistor
= relay
= resistor network
PIV
POLY
PORC
POT
SEMICON
SI
TANT
uF
V
VAR
VDCW
W
ww
S = switch
T = transformer
TB
= terminal block
U = integrated circuit
W = cable
X = socket
Y = crystal
= peak inverse voltage
= polystyrene
= porcelain
= potentiometer
= semiconductor
= silicon
= tantalum
= microfarads
= volt
= variable
= dc working volts
= watts
= wirewound
Model AMM-2B AM Modulation Monitor

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ADJUST
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SWITCH
AMM-2B FRONT PANEL
POWER
ENTRY
FUSE
MODULE
COMPARTMENT
\ I I
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01 I
AMM-2B CHASSIS REAR VIEW
BELAR ELECTRONICS

RF
INPUT
CARRIER H DEMODULATOR H
LEIJEL
SET
115/230 IJAC
50160 HZ
POWER
SUPPLY
PHASE
LINEAR
FILTER
1-----7) +1 51J
1-----7) -1 51J
1-----7) + 51J
MOD
STRIPPER
CAL
--u
~
~
POS
MONITOR
AMPLIF I ER
CARRIER
ALARM
PEAK
DETECTOR
PEAK
MOD
AUDIO
TEST
CARRIER
LEIJEL
'-----""
METER
I
I
J"ck
CARRIER
OFF
INDICATOR
~ MODULATION
METER
PEAK MOD
PEAK
MODULATION
INDICATOR
+125%
MODULATION
DETECTOR
-100%
MODULATION
DETECTOR
+125%
MODULATION
INDICATOR
-100%
MODULATION
INDICATOR
AMM-2B AM MODULATION MONITOR
BLOCK DIAGRAM

The AMM-2B power supply has been modified due to the unavailability of
the MC1468L I.C. (U4) on the A1 board.
BEGINNING WITH SERIAL NUMBER 134026; THE FOLLOWING MANUAL CHANGES APPLY:
1. Disregard the power supply adjustments in steps 3 and 4 of the
"Modulation Meter Alignment Procedure" in the maintenace section
of the manual.
2. The following parts are added to the chassis parts list:
C: FIXED CERAMIC O.luF 50V
IC: 7915C
IC: 7815C
0151-0006
1826-0033
1826-0031
3. The following parts are deleted from the A1 board parts list and
part location table:
C10,C11
C13,C14
Q4
Q5
R25 & R30
R26 & R31
R27,R28
R29 & R32
U4
C: FIXED CERAMIC O.OOluF 1kV
C: FIXED CERAMIC O.luF 50V
TRANSISTOR: 2N3053
TRANSISTOR: 2N4037
R: VAR COMP lOOk
R: METAL FILM 10k 2% 1/4W
R: METAL FILM 4.7 2% 1/2W
R: METAL FILM 51 2% 1/4W
IC: MC1468L
All the affected drawings show both circuit versions.
0151-0002
0151-0006
1850-0008
1850-0011
2100-0019
0751-1032
0771-47G2
0751-5102
1826-0002

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