Belar FMM-2 FM Precision Modulation Monitor


Belar FMM-2 FM Precision


The Belar Model FMM-2 FM Modulation Monitor is a precision wideband, all solid state FM monitor, designed to measure the total modulation characteristics of monaural as well as multiplexed FM transmitters. The Model FMM-2 is also used as a low distortion and low noise FM demodulator to drive the companion stereo and SCA monitors, as well as providing audio outputs for aural monitoring and proof of performance measurements.

The Model FMM-2 has set new standards in totally accurate measurement techniques. Utilizing such advanced design features as an ultra-linear digital discriminator, an almost distortionless and absolutely flat baseband signal is produced to ensure precise stereo and SCA decoding.

In addition to the normal FCC defined semi-peak metering, the FMM-2 incorporates a sample-hold peak modulation meter circuit, independent of modulation polarity, to allow the meter to respond accurately to program peaks.



  • Ultra-linear digital discriminator
  • Digitally selectable peak indicator, adjustable in 1% increments from 1 to 199%, independent of modulation polarity
  • Built-in voltmeter for AM and FM noise measurements
  • Carrier alarm with front panel indicator
  • Two wide-band outputs
  • True peak or semi-peak metering
  • Separate fixed 100% modulation indicator
  • High visibility rear-illuminated meter

Meter Panel MP-8 & MP-9 for the FMM-2
Belar has a number of analog remote meter panels for use with Belar FM monitors. The MP-8 meter panel is designed for use with the FMM-2/FMS-2 FM Monitor set. It features 3 large backlit meters and all the LED’s as the FMM-2 and FMS-2 for easy remote monitoring. It is the same height as the FMM-2 (3 rack-units, or 5.25 inches).The MP-9 meter panel is designed for use with the FMM-2 FM Modulation Monitor. It features one large backlit meter and the same LED’s as the FMM-2 for easy remote monitoring.

PWM-1 Peak Weighting Module for the FMM-2
The Belar PWM-1 Peak Weighting Module is an option (consisting of a circuit board with a rear-panel rotary switch) that adds peak weighting to the Peak Mod and 100% peak lights of the Belar FMM-2 FM Modulation Monitor. The PWM-1 also adds a wideband, 75-ohm buffered composite output to the FMM-2.

Peak weighting is a method for allowing brief modulation peaks to be ignored by your monitor. This will generally result in your monitor indicating a lower peak modulation for a given modulation level.

The PWM-1 Peak Weighting Module can be set to ignore peaks shorter than 3, 5, 9, 15, and 20 cycles (of a 10 kHz burst) as well as Bypass (no peak weighting). The setting is easily changed by turning a rotary switch mounted on the back panel of the monitor.

The PWM-1 can ordered with your new FMM-2, or it can be retrofitted to the FMM-2 you already own. (It will not work with the older Belar FMM-1 or RCA BW-75A Modulation Monitor.) You can add this module yourself, or you can have it installed by Belar. Please contact Belar for more details. If you already own an FMM-2, make sure you provide us with the serial number when you contact us.

Technical Specification

Technical Specification

Frequency Range:       
88 to 108 mHz std. (fixed – specify carrier freq.)

RF Input
1 to 10 volts rms,  50 ohms, BNC connector

Modulation Metering:
Deviation Indication
100% @ +/- 75 kHz, 0 to 133% range

+/-2% @ all modulation levels

selectable: peak (sample-hold) or semi-peak

Noise Measurement:
FM Noise Range
– 50 dB to – 70 dB

AM Noise Range
– 50 dB to – 70 dB

Test Function:
Provides internal standard deviation reference

Provides zero deviation for s/n

RF Level
Calibrates AM noise function and carrier alarm reference level

Carrier Alarm
Indicator adjusted for 90% carrier level

Stereo Monitor
Wideband, 1.5v rms @ 1kohm unbalanced

SCA Monitor
Wideband, 1.5v rms @ 1 kohm unbalanced

Audio, (Program)
+ 10 dBm, 600 ohms, balanced

Audio, (Test)
5v rms, 10k ohms, unbalanced

Audio Output Specifications
Frequency Response
+/- 0.01 dB

Harmonic Distortion
0.01 % max

Intermodulation Distortion
0.01% max (SMPTE)

Signal-to-Noise Ratio
90 dB, min

Remote Outputs:
Carrier Level Alarm
Provides “open collector” output, capable of sinking 20 ma @ 15 vdc

100% Peak Indicator, Adj.

Peak Indicator  
For interface to Model MP-8 Remote Meter Panel (opt)

5.25″H x 10.5″D x 19″W (EIA Rack Mount)

Power Consumption   
10 watts, 117 VAC std. (234 VAC opt) 50/60 Hz

Shipping Weight   
12 Ibs

© Copyright 2000 Belar Electronics Laboratory, Inc. All rights reserved.

New in 2015 – 3 Year Factory Warranty to all Belar Products

Product Resources

Product Resources

Belar FMM-2 Manual

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