FM Subcarrier Monitor

Share on Facebook Share on Twitter


The Model 540 connects to the composite/MPX output of any FM modulation monitor. Setup is simplified with a built-in calibration utility. The 540 is tuned in 1kHz steps to display the injection level of any digital or analog subcarrier between 55kHz and 99kHz. A dual-bandwidth IF accommodates wide and narrow subcarrier signals.

Conventional analog SCAs are demodulated to show the actual subcarrier deviation, and an RS-232 interface is optionally available for downloading and reading RDS/RBDS data groups.


  • Quick and easy interface with any FM Mod-Monitor having a Composite (MPX) output

  • Monitors/Demodulates analog & digital FM broadcast subcarriers

  • Dual-bandwidth IF accommodates wide and narrow subcarrier signals

  • Measures injection level of SCA, RDS and High-speed digital subcarriers.

  • Demodulates audio SCAs and displays actual deviation of SCA program subcarriers

  • Triple-conversion design with precise, crystal-controlled digital tuning

  • Easy calibration to mod-monitor reference – no additional test equipment required

  • Optional comprehensive RDS decoder available (plug-in module is supplied with analysis software)



Subcarrier Tuning Range

54kHz to 99kHz, in 1 kHz increments

Subcarrier Injection Measurements

  • ±1kHz to ±10kHz of main carrier deviation with ±250kHz measurement resolution

  • 1% to 13% of main carrier modulation with 1/3% measurement resolution (100% equivalent to ±75kHz deviation)

Measurement Bandwidth

  • Wide: 12kHz filter for SCA and certain high-speed data channels

  • Narrow: 3.5kHz filter for RDS and similar narrowband data services

SCA Deviation Measurement

  • Absolute: ±1kHz to ±10kHz audio subcarrier deviation with ±250Hz resolution

  • Relative: dB scale covers – 20dB to +2.5dB. “0dB” is factory set to ±5kHz deviation; may be recalibrated by user

Calibration Provision

Total, main-channel carrier deviation is monitored in the CALIBRATE mode, and the INPUT GAIN control is adjusted to reflect the station’s primary mod-monitor readings.


The 38-segment bargraph display is peak-responding and features a peak-hold function.

SCA Audio Response

±0.5dB, 50Hz to 10kHz. Switch-selection of FLAT or 150-microsecond DE-EMPHasis.

SCA Distortion and Noise

Better than 40dB below ±5kHz deviation.

SCA Audio Outputs

Real-panel: Active-balanced SCA program output at 0dBm level

Front-panel: Headphone jack monitors SCA audio, switches to main channel (mono) in CALIBRATE mode.

Composite (MPX) Input

Unbalanced, 100k-Ohm-bridging: requires 1V p-p or greater input signal level representing ±75kHz main channel deviation.

SCA Decode Option

Easily-installed plug-in module formats RDS data to RS-232 standards. Supplied software enables detailed RDS data analysis with any IBM-compatible PC.

Power Requirements

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