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 display provides a 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, of the carrier frequency exceeds ±10 Hz, a front panel LED indicator is immediately actibated into a flashing state. This warns of an impending off-frequency condition. After three successive counts in this condition, the monitor will actibate 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 sucessive 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 frequenct 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.
Inhibited off-frequency alarms
±10 Hz Off-Frequency Alarm
±20 Hz Off-Frequency Alarm
RF Level Alarm
Invalid Count Alarm
Count Inhibit AlarmPILOT
External timebase input
1 MHz output
Large 3½ digit LED display
Low profile design
Designed for ATS Operation