Belar: "When accuracy counts, count on Belar"


AMM-3 photo


The Belar AMM-3A AM Modulation Monitor is an all-solid-state precision AM demodulator which exceeds the US Federal Communications Commission standards for measuring the total modulation characteristics of medium-frequency AM broadcast transmitters. The detector circuitry of the AMM-3A is non-frequency discriminating, so the unit is suitable for use with shortwave transmitters as well. The AMM-3A employs a unique analog divider circuit which maintains the accuracy of all indications despite changes in carrier level. Simultaneous indications of negative and positive modulation appear on two semi-peak reading meters. Negative and positive modulation peaks are simultaneously indicated on two thumbwheel-programmable peak indicators, as well as individual fixed negative 100% and positive 125% modulation peak indicators. Front-panel pushbuttons select meter indications of relative carrier level and AM noise. The AMM-3A incorporates a carrier-level alarm which indicates when the carrier level falls outside the range required for accurate indications. Also included are an adjustable modulation-level alarm, and a calibration reference to check the accuracy of the readings at any time. An internal jumper can be set to apply the USA NRSC de-emphasis characteristic to the audio outputs.



RF Frequency Range                 200 kHz to 50 MHz

RF Sensitivity                     5 Vrms to 10 Vrms

RF Input Impedance                 1000 ohm standard, 50 ohm optional

RF Input                           Rear-panel BNC connector

Positive Modulation Meter Range    0% to 133%

Negative Modulation Meter Range    0% to 100%

Accuracy			   2%

Peak Modulation Indicators:
   Negative peak range		   1% to 99% in 1% increments
   Positive peak range		   1% to 199% in 1% increments

Fixed Indicators		   -100%, +125%			
Frequency Response		   +0.0 dB, -0.5 dB, 20 Hz to 15 kHz

Envelope Pulse Response		   Overshoot <1%

Modulation Level Alarm		   Adjustable threshold, 
					fixed timeout (-15 seconds)

Carrier Level Meter Range          0% to 133%

Carrier Limit (Loss) Alarm	   50% & 133% relative level

Audio Monitoring Output		   +20 dBu (4.9 Vrms), 600 ohm active-balanced

Audio Test Output (proof of
	performance)		   2.5 Vrms, rear-panel BNC connector

Auxiliary Detector Output	   5 Vrms

Audio Response			   +0.0 dB, =0.5 dB, 20 Hz to 15 kHz
				 	(detector response -3 dB at 50 kHz)

Distortion			   0.25% maximum at 99% modulation

Signal-to-Noise Ratio		   >_80 dB (de-emphasis out)

AM Noise Level Metering Range	   -40 dB to -70 dB

Remote Outputs:
   Adjustable negative and positive peak indicators,
   -100% and +125% peak modulation indicators;
   positive and negative remote modulation meters,
   carrier level reference, modulation level alarm,
   carrier limit (loss) alarm

Operating Temperature		    0C to +50C

Power Consumption		    8 watts, 100-240 VAC, 50-60 Hz

Dimensions			    5"H x 19"W x 8" D (EIA rack mount)

Shipping Weight			    11 lbs. (5 kg)

© Copyright 2013 Belar Electronics Laboratory, Inc. All rights reserved. Specifications subject to change without prior notice.

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