AM Modulation Monitor

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See Model 526 As Replacement

The 525N is a third-generation AM Modulation Monitor from Inovonics. It can accept either a direct feed from the transmitter, or function as a precision Reference Receiver to give accurate off-air measurements reflecting ATU, phasor and antenna parameters.

A proprietary phase-locked synchronous detector provides precise demodulation, rejects interference, and recovers only the amplitude-modulated component of HD Radio™ ‘hybrid digital’ transmissions.

The 525N is also compatible with power-saving MDCL operation. Although the 525N maintains full wideband response for measurement, it features user-selectable audio-monitor cutoff characteristics to mitigate noise or to simulate the response of consumer radios.

IP connectivity with full SNMP support gives the user total access to the unit from any computer, tablet or mobile device. Setup, metering, alarms and audio monitoring are all available from the remote monitoring point.

The 525N is supplied with a large-aperture, weatherproof passive AM Loop Antenna.


  • Accurate, simultaneous display of positive and negative peak modulation with Peak Density histogram

  • Absolute-limit and user-programmable Peak Flashers

  • Calibrated RSSI signal strength display and asynchronous noise readout

  • Alarms for Low Signal, Audio Loss and Overmodulation with panel indicators and ‘tally’ closures

  • Full Web interface gives total remote control of all setup parameters, metering, alarms with logging, and streamed audio monitoring

  • 5 Station Presets

  • 10kHz/9kHz channel spacing

  • Balanced audio output

  • Supplied with out- door passive AM Loop Antenna

  • Headphone jack

  Online Demo Available


Inovonics 525N AM Modulation Monitor

- Alan Alsobrook Checking it Out - Inovonics 525N AM Modulation Monitor



Receiver Topology

Single-conversion superheterodyne; 300kHz IF; phase-locked I/Q synchronous detector.

RF Inputs

The 75-ohm (F) antenna input connects to the supplied broadband passive AM Loop Antenna. Cable is not included, but up to 100 feet of general-purpose RG-6 CATV coax may be used. A short wire antenna may prove adequate in high-signal areas that suffer minimal interference. A 50-ohm (BNC) high-level input accepts a direct RF sample between 1V and 7V r.m.s. / 3V–20V p-p.

Tuning Range

Tunable via the front-panel menu or the Web interface:

  • 520kHz to 1720kHz in 10kHz steps
  • 522kHz to 1719kHz in 9kHz steps Five station-memory pushbutton/Web presets are provided.


Measurement Bandwidth

Carrier amplitude demodulation extends to 10kHz, ±0.2dB. Measurement is not affected by the user-selectable audio cutoff.

Audio Response

User-selectable “FLAT” response, or restricted in programmable 1kHz steps between 10kHz and 2kHz.


A menu command switches-in the NRSC ‘truncated’ 75μs de-emphasis characteristic to the program audio outputs with any restricted audio bandwidth selection.

Audio Distortion

Typically 0.15% THD at 50% carrier modulation; <0.5% at 99% modulation


Modulation Display

The peak-responding front-panel bargraph readout shows positive and negative modulation peaks simultaneously, with extended persistence of the most recent highest peak value. Measurement resolution is 1% between 50% and 100% (negative) and 50% and 140% (positive) modulation, and 2% between 20% and 50% modulation.

RSSI and Noise Display

The Modulation Display may be switched to show the dBuV level of the incoming carrier (RSSI) and a relative measurement of asynchronous noise.

Peak Flashers

  • Absolute-limit flashers are factory-calibrated at –100% and +125% carrier modulation.
  • A second set of flashers may be programmed by the user to values between –70% and –100%, and +70% and +140%.


Program Audio Outputs

  • The active-balanced, rear-panel program audio output (XLR) delivers +4dBu from a 200-ohm resistive source.
  • Front-panel headphone jack (¼-inch, TRS)


Open-collector NPN transistor outputs (screw-terminal block) for low signal, program audio loss and overmodulation. Closure polarity is programmable.



RJ45 jack for remote setup and operation via TCP/IP; DHCP or Static IP with local or remote selection

Remote Monitoring

Remote Web-based monitoring of off-air audio


Comprehensive network configuration utility including dynamic DNS and full SNMP support with downloadable MIB file.


Supports email and text message services with or without SSL.


Power Requirements

105–130VAC (0.250A Fuse) 210–255VAC (0.125A Fuse),50/60Hz; 10W.

Size and Weight

1¾”H x 19”W x 7”D (1U); 9 lbs. (shipping).


Continuous operation at ambient temperatures between 32ºF/0ºC and 122ºF/50ºC; 0-95% relative humidity, non-condensing, altitudes to 10,000ft/3,048m.