AM Modulation Monitor

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The Model 525 is our second-generation AM Mod-Monitor. It was specifically developed to give accurate AM readings with Hybrid Digital (IBOC) transmissions. The 525 is menu-driven with a peak-hold LCD display showing simultaneous positive and negative modulation, incoming RF level and asynchronous noise.

Measurement bandwidth extends to more than 10kHz, but a programmable low-pass audio filter can simulate the response of consumer radios or the effects of transmission bandwidth constraints. The 525 is supplied with an outdoor large aperture loop antenna.


  • Easy menu-navigated setup and operation

  • Bright LCD display

  • Frequency-agile design gives accurate off-air measurements

  • Maintains AM accuracy with IBOC digital transmissions

  • Front-panel alarms and rear-panel tallies for: ◦ Overmodulation ◦ Carrier loss ◦ Audio loss

  • Five programmable memory presets for easy station access

  • Audio response is independent of measurement bandwidth and may be programmed in 1kHz steps between 10kHz and 2kHz

  • Supports SNMP

  • Weatherproof, directional loop antenna (with mounting bracket)



Tuning Range

Tunable from the front panel between 520kHz and 1720kHz in 10kHz steps; five station-memory pushbuttons.

Peak Flashers

Absolute-limit flashers (alarmed) are factory-calibrated at –100% and +125% carrier modulation. A second set of flashers may be set from the front panel in 1% increments between –70% and –100% and +70% and +140%.

RF Inputs

  • Antenna: This 75-ohm (F) input is specifically intended for the large aperture loop antenna provided. Cable is not included, but up to 100 feet of common RG6 TV coax may be used

  • Direct: A high-level (BNC) input accepts a direct RF sample from the transmitter between 1V and 7V r.m.s.

Measurement Bandwidth

Carrier amplitude demodulation extends from 20Hz to 10kHz, ±0.2dB. Modulation measurements are not affected by the user-selectable audio cutoff or NRSC de-emphasis.

Audio Response

Audio at the program line output and headphone jack may be menu-selected for “FLAT” response, which follows the full-bandwidth modulation measurement characteristic, or restricted in 1kHz steps between 10kHz and 2kHz (–3dB point) per the graph below.

Audio De-Empahsis

A menu command turns NRSC ‘truncated’ 75μs de-emphasis on and off in the program audio and headphone outputs with any user-selected audio cutoff option.

Audio Distortion

Less than 0.5%THD at 100% carrier modulation

Audio Noise

Typically better than 55dB below 100% modulation at an S9 carrier level with 10kHz audio bandwidth and NRSC de-emphasis selected.

Audio Outputs

The active-balanced (XLR) program audio output delivers +4dBm at 100% modulation. A front-panel headphone jack (1/4-inch TRS) also monitors the demodulated audio.


Front-panel indications and open-collector NPN transistor ‘tally’ outputs signal OVERMODULATION, CARRIER LOSS and PROGRAM AUDIO LOSS conditions.

Power Requirements

105-130VAC and 210-260VAC; 50/60Hz; 20W

Size and Weight

23” x 16” x 5” (2U); 12 lbs

584mm x 406mm x 127mm ; 5.4 kg