AMDA-1 AM FREQUENCY MONITOR

Description

The Belar AMM-4 is a digital AM frequency monitor designed especially for automatic broadcast transmitter monitoring. The counter will accurately monitor any fre­quency from 10 kHz to 50 MHz. A large 3½ digit LED readout provides a display range of ± 1999 Hz devia­tion from the assigned channel. A front panel LED in­dicator warns of low RF level or loss of carrier; an op­tional relay contact can be provided. The monitor also provides two off-frequency alarms which are inhibited so that three successive errors are required to signal an alarm. This prevents false off-frequency conditions. For example, if the carrier frequency exceeds ± 1 O Hz, a front panel LED indicator is immediately activated into a flashing state. This warns of an impending off­frequency condition. After three successive counts in this condition, the monitor will activate an optional relay contact for remote alarms. It also changes the front panel indicator to a continuous ON state. If the fre­quency exceeds ± 20 Hz for three successive counts, then the second front panel indicator is activated as well as an optional relay contact.

Another feature of the AMM-4 is the invalid count alarm.If this condition arises due to low RF level or a malfunction in the counter, the frequency alarms are held in their OFF condition; however, a front panel LED indicator and optional relay contact are provided to warn of an invalid count.

If the counter is driven by a modulated source, a count inhibit input is provided. This input is controlled by the 100% negative output of a modulation monitor; thus if the modulation level exceeds 99% negative, then the display and alarms would be held at the state they were in prior to the overmodulation fault.

Relay contact outputs (described above) are available as options. A switchable 1 MHz input/output connector is provided for frequency comparison.