Off-Air FM Modulation Monitor

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lnovonics’ 530 answers the very real need for a simple, yet accurate and affordable FM “Mod-Monitor.” It combines a wideband FM receiver with very linear demodulation and metering circuitry for precise measurement of FM broadcast carrier modulation.

High-resolution displays give reliable readings of Total Modulation, demodulated Program Audio, and Pilot/Subcarrier injection levels. The incoming RF signal and multipath distortion components are also monitored to ensure that indicated measurements are truly valid.


  • Carrier Modulation scale displays Total Mod. or independent positive/negative deviation in three ranges and resolutions.

  • Adjustable Peak Flasher is easily set in one-percent increments.

  • Stereo Pilot injection level is shown in percent and dB

  • Demodulated Stereo Program metering



Tuning Range

-87-108MHz continuous coverage with 8 station presets.

Receiver Sensitivity

  • -2511V (40dBf) for 20dB mono quieting
  • -250~1V (60dBf) required for valid Total Modulation Reading

RF Inputs

  • “F” connector for 75-ohm antenna
  • “BNC” connector for alternate 50-ohm RF sample; 10 volts r.m.s.. max.

Carrier Modulation Display

  • Quasi-peak response with peak-hold display.
  • User-selectable integrations of O.lms. 0.2ms. 0.5ms. 1ms.
  • Bargraph display monitors + peaks.- peaks. +-peaks and 19kHz Stereo Pilot.
  • Scaling is selectable at 7 5% to 120% in 1% Increments.
  • 30%to 150% in 2.5% Increments. and 3% to 15% in 0.25% Increments.
  • 100% modulation corresponds to +-75kHz carrier deviation.
  • Total Modulation measurement accuracy IS 51%. -tl metering division.

Peak Flasher

  • Adjustable between 90% and 120%
  • Remote flasher output

Composite Input/Output

Rear-panel BNC connector and IN/OUT switch permit external monitoring of baseband signal from off-air source, or provide input to stereo demod and metering for external baseband feed. Approx. 2 volts p-p corresponds to 100% modulation. 75-ohm output Impedance; lOk-ohm input characteristic.

Baseband Response

Amplitude response of demodulated Composite signal: +0, -0.5dB. 10Hz-60kHz; less than 1.5dB down at 100kHz.

Demod Metering

Dual displays show Left, Right, Stereo Sum, Stereo Difference. 19kHz Pilot, 38kHz Residual, Multipath Distortion and RF Signal Level. Quasi-peak response on +lOdB to -39dB scale, averaging response with additional 30dB gain on -2OdB to -69dB scale. ldB/step metering resolution.

Stereo Demod Performance

  • Program Audio Response: i0.5dB. 20Hz-15kHz
  • Noise: Unmodulated (stereo) carrier noise better than 70dB below 100% modulation with de-emphasis.
  • Stereo Separation (Composite Input): better than
  • 50dB. 50Hz-15kHz
  • Stereo Separation (Off-Air): better than 40dB, 50Hz-10kHz; 35dB or better at 15kHz.
  • Crosstalk Measurement: M/S and S/M crosstalkmeasurement by stereo sum/difference method andlimited by stereo decoder circuitry. 50dB measurementresolution. 20Hz-5kHz.

Program Signal De-Emphasis

  • Switchable IN/OUT from front panel.
  • May be jumpered for 75us or 50us.

Audio Outputs

  • Front-panel headphone jack monitors program audio.
  • OdBu unbalanced outputs at rear-panel BNC test connectors.
  • OdBm, 600-ohm balanced program line outputs at rear-panel USER INTERFACE connector.

User Interface

Measurements, Indicators and alarms are brought-out to a rear-panel DB-25 connector so that any monitoring function may be duplicated at a remote location.

Power Requirements

-105-130VAC and 210-260VAC, 50/60Hz; 15W.

Size and Weight

-3.5”H x 19”W x 12”D (2U): 11 Ibs.