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AMM-4 Photo



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 3 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.



Frequency Range                         10 kHz to 50 MHz

Display                                 Large 3 digit LED

Display Range                           1999 Hz

Sensitivity                             100 mV, Unmodulated

                                        2 Vrms, 99% modulation

Gate Time                               2 seconds

Resolution                              0.5 Hz

Time Base (internal)                    6 MHz

Stability                               1 x 10^-6 per year

Time Base (External)                    1 MHz TTL compatible level

10 Hz alarm                             Front panel LED, inhibited for

                                           three successive errors

20 Hz alarm                             Front panel LED, inhibited for

                                           three successive errors

RF alarm                                Front panel LED, warns of low RF

                                           level or carrier fail condition

Invalid Count Alarm                     prevents false counts

                                           due to low RF level or problem in counter

Count Inhibit Input                     External contact required

                                           capable of sinking 2mA

Level Alarms                            3 LED Indicators

Dimensions                              1.75"H x 10.5"D x 19"W

                                         (EIA Rack Mount)

Power Requirements                      115/230 VAC, 50/60 Hz

© Copyright 2000 Belar Electronics Laboratory, Inc. All rights reserved. Specifications subject to change without prior notice.

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