Belar AMM-4

The Belar AMM-4 is a digital AM frequency monitor specifically designed for automatic broadcast transmitter monitoring. It operates within a frequency range of 10 kHz to 50 MHz and features a large 3½ digit LED display, providing precise monitoring with a range of ±1999 Hz deviation from the assigned channel.

To enhance monitoring capabilities, the AMM-4 includes various indicators and alarms. A front panel LED indicator warns of low RF level or loss of carrier, with an optional relay contact available. The monitor incorporates two off-frequency alarms, which require three successive errors to trigger an alarm, preventing false off-frequency conditions.

In case of an impending off-frequency condition, such as the carrier frequency exceeding ±10 Hz, a front panel LED indicator starts flashing. After three successive counts in this state, the monitor activates an optional relay contact for remote alarms and changes the front panel indicator to a continuous ON state. If the frequency exceeds ±20 Hz for three successive counts, a second front panel indicator is activated, along with an optional relay contact.

The AMM-4 also features an invalid count alarm to address issues like low RF level or counter malfunctions. In this condition, frequency alarms are held in their OFF state, but a front panel LED indicator and optional relay contact warn of an invalid count.

For situations where the counter is driven by a modulated source, a count inhibits input is provided. This input is controlled by the 100% negative output of a modulation monitor. If the modulation level exceeds 99% negative, the display and alarms are held at their previous state, preserving the monitoring status before the overmodulation fault.

Additionally, the AMM-4 offers relay contact outputs as optional features, and it includes a switchable 1 MHz input/output connector for frequency comparison purposes. This comprehensive set of features makes the Belar AMM-4 a reliable and versatile tool for broadcasters, ensuring accurate and efficient monitoring of AM frequencies.