Racal Instruments SCM-1

The Racal Instruments SCM-1 is a solid-state, crystal-controlled superheterodyne SCA (Subsidiary Communications Authorization) adapter designed for direct integration with FM broadcast monitors such as the FMM-1 or FMM-2. This FCC Type Approved instrument measures and demodulates SCA subcarriers to monitor center frequency deviation, modulation characteristics, and peak modulation levels in FM broadcast applications.

– Technical Specifications

The SCM-1 employs a 260 kHz IF strip with a stable, broadband frequency discriminator for accurate subcarrier demodulation. Four switched crystal positions enable sequential monitoring of up to four independent subcarriers. The instrument features a peak reading modulation meter with independent peak modulation indication responsive to both positive and negative peaks. A sensitive average voltmeter circuit facilitates precise measurements of injection level, crosstalk, and noise across the monitored signal.

– Key Features

• SCA center frequency deviation meter for real-time monitoring
• Demodulates and measures SCA subcarrier signals with high fidelity
• Peak modulation light independent of polarity—responds to positive and negative peaks
• Modulation calibrator integrated for direct meter calibration verification
• Four crystal-switched positions for independent subcarrier selection
• Metering circuits standardized with FMM-1 and FMM-2 FM monitors for seamless integration
• Permits measurement of incidental AM, AM noise, SCA injection, and SCA modulation parameters
• Standard 5.75 × 19 inch rack-mount chassis for broadcast facility integration
• Shielded internal compartment for factory adjustments; seldom-used controls located behind hinged name-plate cover

– Typical Applications

FM broadcast monitoring and SCA subcarrier analysis in remote and local monitoring stations. Direct integration with existing FM monitor infrastructure. Real-time demodulation and measurement of multicarrier FM signals in SCA-equipped broadcast systems.

– Compatibility & Integration

Designed for direct interconnection with Racal Instruments FMM-1 and FMM-2 FM monitors. Rear-panel connectors include AC power input, baseband input, and monitor outputs. Metering standardization ensures compatibility with established FM broadcast measurement protocols.