Belar AMM-3A

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.


  • Two modulation meters for simultaneous measurement of positive and negative modulation
  • Two adjustable peak modulation indicators, thumbwheel programmable from 1-99% negative and 1-199% positive modulation.
  • Separate, dedicated 100% negative and 125% positive peak indicators
  • All modulation indications independent of carrier level
  • Semi-peak reading modulation meters respond accurately to short duration program peaks
  • Built-in Carrier Level Limit (Loss) and Modulation Level Alarms with dry relay contact outputs
  • Built-in modulation calibration check
  • Linear-phase detector filter provides accurate modulation indications without overshoot.
  • Switchable NRSC de-emphasis