HD Radio Modulation Monitor

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Incorporating all the necessary features for station setup, regulatory compliance, and remote monitoring, Inovonics' 551 HD Radio Modulation Monitor is the ultimate choice for advanced FM and HD Radio signal monitoring, whether you are at the transmitter site or halfway around the world. Simultaneously monitor in real time the off-air FM modulation along with up to 4 HD Radio Channels.

A high-resolution 7-inch TFT Touch Screen displays all the essential modulation data for accurate readings in a graphic format. The 551 collects the history of signal parameters and displays HD Radio™ album artwork, station logos and similar visuals on the front panel display and remote Web interface. The 551 includes a built-in BandScanner™, a real-time clock and full SNMP functionality

Rear-panel alarms constantly check for Audio Loss, RF Loss, Multipath and Overmodulation, while advanced notifications alert personnel with e-mail or SMS messaging when any or all of the alarms occur. SNMP is fully supported.

Advanced FM & HD Radio signal monitoring


  • Monitor off-air analog FM and HD Radio signals (HD1-HD8) on the Hi-Res Front Panel Touch Display and via the Web from anywhere in the world.

  • The 3U package features a 7-inch graphic touch screen display, wide-range LED level meters with rear-panel tallies.

  • The 551 collects the history of signal parameters and displays HD Radio™ album artwork, station logos and similar visuals on the front panel display and remote Web interface.

  • Front-panel alarms and/or rear-panel ‘tallies’ indicate Audio Loss, Low Signal, RDS Errors, HD Loss, HD Power, FM/HD1 Alignment, HD Artist Experience, and many others.

  • Spectrum graphs include RF Baseband, MPX and Left/Right Audio. O-Scope views for MPX, Pilot, RDS and all Audio Channels.

  • Measures real-time audio diversity delay between the FM and HD1 broadcast.

  • Fulltime off-air program audio is available simultaneously as L/R-analog, AES3-digital and Dante®-based AES67 AoIP streaming, all with adjustable levels, plus a multi-listener Internet IP stream and front-panel headphone jack.

  Online Demo Available


GS Broadcast Embraces Inovonics 551/552

- Radio World, November 2, 2022 G.S. Broadcast Technical Services in Ontario, Canada, Embraces Inovonics 551/552

I was GOBSMACKED. Not only was the 551 everything it needed to be, it was a real breakthrough in monitoring compliance for FM broadcasters.

- David K Peabody - BSL, LLC dba Broadcast Signal Lab

Congratulations! What a terrific product. When we were developing HD Radio I believed we needed an IBOC quality monitor, this surpasses anything that I envisioned. Terrific job.

- Glynn Walden - Founding Partner and VP Engineering USADR/iBiquity



Tuning Range

87.5MHz-107.9MHz in 100kHz steps

Antenna Input:

75-ohm (F)

High Level RF Input:

50-ohm (BNC)


10dBuV required for 50dB mono-FM SNR, unweighted.

Reception Modes:

FM: Stereo / Forced Mono

HD Radio: HD1 through HD8

FM/HD1: ‘Split Mode’ delivers L+R FM to the left audio channel and L+R HD1 to the right.

Off-Air Frequency Response:

FM: ±.1dB, 20Hz-15kHz

HD Radio: ±0.25dB, 20Hz-20kHz

Stereo Separation:

FM: 60dB, 20Hz-15kHz

HD Radio: 90dB, 20Hz-20kHz


FM: <0.01% THD, 20Hz-15kHz

HD Radio: <0.003% THD, 20Hz-20kHz

FM De-emphasis: 75µs, 50µs or None, menu-selectable

Program Audio Outputs:

‘Assignable’ outputs utilize XLR connectors, ‘Dedicated’ outputs are RJ45 jacks per StudioHub® spec. (model 551 only)

Balanced Analog: Left and Right outputs adjustable from –15dBu to +15dBu in 0.1dB steps; 200Ω source.

AES Digital: Adjustable from –30dBFS to 0dBFS in 0.1dB steps; 44.1kHz sample rate; 110 Ω transformer-coupled.

Dante/AES67 Compatible: (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.

Headphone Jack: (¼” TRS) with adjustable listening level.

Listening Stream: Web browser ‘remote listening’ stream uses 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.

Composite/MPX Output: (BNC) may be switched between MPX and 19kHz stereo pilot sample; adjustable from 1Vpp to 6Vpp in 0.05V steps.

LAN Port:

LAN connection to local network or Internet provides remote monitoring, control, listening and full SNMP implementation; user-programmable network setup and streaming parameters.

General Purpose Outputs:

Ten individual open-collector NPN transistor closures to ground are associated with alarm functions. Each is programmable for GPO assignment and logic polarity.

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 & use statistics.

HD PAD Data Displayed:

Overview: Short Name Universal Name •
Station ID • Slogan• Message Station
Location Service Mode TX Blend Emergency Alert

HD1-HD8, each:

Slogan Program Type • Artist Title Album Codec Mode • Bitrate TX Gain Logo/Artist Experience graphics and file details.

Bargraph & Numerical Level Metering:

Analog FM: Carrier Modulation Stereo Pilot & Subcarriers Demodulated L/R & L+R/L-R Stereo Separation Stereo Crosstalk BS.1770 Loudness Synchronous & AM Noise.

HD Radio: (simultaneously for HD1 and three other preselected HD programs)
L/R Audio BS.1770 Loudness (absolute and relative to Analog FM Loudness).

FM/HD1 Alignment: Timing offset and level and phase discrepancies between programs; ‘Confidence Factor’ display.

Graphic Displays/Plots: RF Spectrum MPX Spectrum Audio Spec­trum Audio XY Audio O’scope FM Modulation History Audio Level History Metrics History FM/HD1 Time & Level Alignment History BandScanner™ utility.

Alarms: Most alarms have multiple parameter settings. All alarms can send text or email notifications. Alarms are also logged: daily, weekly, monthly._

Analog FM: Carrier Overmod Audio
Loss Low Signal RDS Loss PI Error RT Update Pilot Loss

HD Radio: HD Loss Program Loss • Audio Loss HD Power Level FM/HD1 Alignment PSD Update Logo Receipt Artist Experience Update Image Issues Emergency Alert Updates

Real-Time Clock:

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

Power Requirement:

88-264Vac, 18W.

Operating Environment:

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

Size and Weight:

25”H x 17”W x 3”D; 8 lbs. shipping weight.