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