FM Modulation Monitor

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The 541 is Inovonics fourth-generation FM Modulation Monitor. It delivers a wealth of information about the transmitted signal in terms of the RF carrier and all subcarriers, the audio component defining the technical quality that the listener hears, and full decoding of RDS data and SCA audio.

The all-digital 541 combines detailed DSP signal analysis with a menu-driven touch­screen display, plus Webserver-based total access for remote operation, including measurements, graphical data and direct Web-browser audio monitoring of the off-air program.

The Ultimate FM Signal Monitoring Solution


  • Unexcelled off-air reception of analog-FM broadcasts with highly-accurate displays of total modulation and other measurements, even in the presence of on-channel or adjacent-channel HD Radio carriers at any level.

  • Intuitive, menu-driven setup from the front panel, or remote setup and operation with the built-in Webserver that may be addressed over any IP network by computer or mobile device. The 541 supports full SNMP remote control and monitoring.

  • Graphic front-panel and remote display of all level metering; FFT spectrum analysis of IF passband, MPX baseband and program audio; oscilloscope display of program audio and stereo XY.

  • Alarms for a range of signal faults, with tallies and SMS/text or email message dispatches to specific individuals for various alarm conditions. All alarms are logged chronologically as well.

  • Analog, AES3-digital, HTTP/UDP Web-streaming and independent AoIP-streaming program audio outputs, plus an FM composite/MPX baseband output.

  • The BandScanner™ utility scans the FM spectrum and displays each station with its signal level, PI code and call sign.

  • StationRotation™ mode enables automatic sequential monitoring of multiple station presets.

  • Collects and logs a history-over-time of FM and audio signal parameters.

  • Accurate program loudness measurement to the human perception ITU-R BS.1770 (‘LU’) loudness specification.

  • Stays on-channel and retains measurement setups through signal and power losses.

  Online Demo Available



Specifications tabulated here are actual, real-world measurements, not optimistic allusions to theoretical ideals. Measurement results should be repeatable when using the appropriate, laboratory-grade test equipment.


Tuning Range:

Tunes 76.0MHz-108.0MHz in 100kHz steps.

Antenna Input:

75-ohm (F), 1VRMS max.

High-Level RF Input:

50-ohm (BNC), 5VRMS max.

Off-Air Sensitivity (for 50dB monaural SNR):

  • 5dBµV or better with de-emphasis.
  • 15dBµV or better unweighted.

Reception Modes:

Stereo / Forced Mono / SCA Program Audio


(Off-Air or High Level; (D) indicates measurements taken with de-emphasis.)

  • Frequency Response: ±0.25dB, 10Hz-100kHz.
  • Signal-to-Noise (D): >83dB.
  • Distortion (D): <0.01% THD+N; <0.01% IMD (SMPTE, 60Hz/7kHz, 4:1).
  • FM Deviation: Indicates composite (total) and independent positive and negative deviations. ±75kHz = 100% Modulation; 0-200% metering with ±1% accuracy. *AM Noise (D): Measures down to 87dB below 100% AM Modulation.
  • FM Stereo Pilot: Indicates 0-15% pilot injection; pilot frequency readout has ±0.1Hz accuracy.
  • FM Subcarriers: Indicates percent injection of 38kHz (residual), 57kHz RDS, 67kHz/92kHz SCA subcarriers.


(Off-Air or High Level; taken with de-emphasis; (M) indicates measurements taken in monaural reception mode.)

  • Frequency Response: ±0.1dB, 20Hz-15kHz.
  • Signal-to-Noise (M): Analog Out: <0.01% THD+N; <0.02% IMD (SMPTE, 60Hz/7kHz, 4:1). Digital Out: <0.01% THD+N; <0.01% IMD (SMPTE, 60Hz/7kHz, 4:1).

  • Stereo Separation: >64dB, 20Hz-15kHz
  • FM Stereo Crosstalk (Main-Sub or Sub-Main): >67dB, 20Hz-15kHz,.
  • FM De-emphasis: 75µs / 50µs / None.


MPX Output:

(BNC) select either MPX or 19kHz stereo pilot sample; adjustable from 1VPP to 6VPP in 0.01V steps; ±0.25dB, 10Hz-100kHz.

Program Audio Outputs:

May be assigned to the FM-stereo program or to SCA audio. Unless otherwise noted, performance parameters reflect FM Stereo Performance cited above.

  • Balanced Analog: (XLR) Left and Right outputs adjustable from –15dBu to +15dBu in 0.1dB steps; 200Ω resistive source.
  • AES Digital: (XLR) Adjustable from –30dBFS to 0dBFS in 0.1dB steps; user-selected 44.1kHz or 48kHz sample rate; 110Ω transformer-coupled.
  • Dante/AES67 Compatible AoIP Port: (RJ45) Output at 44.1kHz (Dante-only) or 44.1kHz/48kHz (Dante/AES67); AoIP utility has independent IP, Audio Format and Transmit Flow settings; level adjustable from –30dBFS to 0dBFS in 0.1dB steps.

Program Audio Outputs (continued):

  • UDP Stream: ADTS or ADTS in MPEG-TS transport.
  • HTTP/Icecast ‘Casual’ Listening Stream: Web browser remote-listening stream employs HE-AACv2 encoding, 44.1kHz or 48kHz sample rate, bit-rates from 18kbps to 64kbps; accommodates up to 10 simultaneous listeners. HTTP/Icecast and raw UDP streams are available simultaneously.
  • Headphone Jack: (¼” TRS) Menu-adjustable listening level.
  • LAN Port: (RJ45) LAN connection to local network or Internet provides remote monitoring, control, listening and full SNMP implementation; user-programmable network setup and streaming parameters.
  • LAN Port: (RJ45) LAN connection to local network or Internet provides remote monitoring, control, listening and full SNMP implementation; user-programmable network setup and streaming parameters.


Bargraph & Numerical Level Metering:

  • Carrier Modulation • Stereo Pilot & Subcarriers.
  • MPX Power • Demodulated L/R & L+R/L-R
  • Stereo Separation • Stereo Crosstalk • BS.1770 Loudness • SCA Levels • Synchronous & AM Noise.

Graphic Displays and History Plots:

  • IF Spectrum • MPX Spectrum • Audio Spectrum • Audio Oscilloscope • Audio XY • FM Modulation History.
  • Audio Level History • RF Metrics History.
  • BandScanner™ utility.

RDS Fields Displayed:

  • PS • PI • Call • RT • RT+1 • RT+2 • PTY • PTYN • CT • M/S • DI • TP • TA • AF • ODA • Block Error Rate • Groups & Group Use Statistics.


Real-Time Clock:

  • Auto-sets to Internet time; auto/manual DST setting; battery backup.

Local & Remote Alarms:

  • Carrier Overmod • MPX Power • Audio Loss • Low Signal • Pilot Loss • Multipath • RDS Loss • RDS PI Error • RDS RT

  • RDS CT • RDS TMC • Pilot Loss • MPX Power. (Most alarms have multiple parameter settings. All alarms can send text or email notifications. Alarms are automatically logged daily, weekly and monthly.)


Power Requirements

88-264VAC, Single-Phase; 12W.

Size and Weight

3.5”H x 19”W x 9”D (2U); 10 lbs. (shipping weight)

Operating Environmental

32°F/0°C-122°F/50°C; 0%-95% non-condensing relative humidity; 10,000ft/3048m.


  • CE: EN50081-1 / EN50082-1, 93/68/EEC
  • RoHS: 2002/95/EC.