Summary
The Belar SCMA-1 Digital FM SCA Modulation Monitor and Analyzer is a DSP based precision SCA monitor designed to operate in conjunction with the Belar FMMA-1 or FMM-2 Modulation Monitor or other source of wideband composite.
Features
The SCMA-1 digitizes the composite and decodes the selected subcarrier signal using digital signal processing techniques. Unlike an analog design, a DSP based design is not subject to variations due to temperature, component aging, or component tolerances. The resulting circuit requires no adjustments, but can achieve extremely tight tolerances. In addition, the DSP design allows the use of FIR linear phase filters whose bandwidth can be varied via the front panel. The use of variable bandwidth filters allow the user to optimize the subcarrier BPF and detector LPF cutoff frequencies for a particular SCA modulation scheme. The use of DSP processing also eliminates the need for separate crystal oscillators for each subcarrier frequency, instead all available frequencies are synthesized from a common system clock.
The SCMA-1 implements all its metering and measurement functions using DSP processing. Therefore, the SCMA-1’s calibration does not depend on any adjustable circuit components or their tolerances. This guarantees the calibration of the unit will remain stable over time. By digitizing the measurements the user can display modulation peaks, injections, and dB readings directly. As an added benefit, all readings can be viewed remotely using an IBM compatible personal computer.
Technical Specification
Technical Specification
Metering
Total, Main (L+R), Subcarrier modulation
0-150%, 1% increments, peak reading
Main (L+R), Subcarrier Modulation
+3.5 to -99 dB, 0.5 dB steps, autoranged RMS reading
Subcarrier injection
0.0-25.5%, 0.1% increments
Subcarrier
Frequency Range
41.0-100.0 kHz, 0.5 kHz steps
BPF Bandwidth
1-16 kHz, 1 kHz steps
Detector Bandwidth
1-8 kHz, 1 kHz steps
Deviation Sensitivities
100%=1.0-7.0 kHz, 0.1 kHz steps
Internal Calibrator
67 kHz, 6 kHz dev, 1 kHz mod @ 10.0%
Input
Composite
1.0 – 2.0 Vrms (2.8V – 5.7V P-P), 100 k ohms, unbalanced, BNC Connector
Outputs
Main (L+R) Audio
+10 dBm, 600 ohms, balanced, XLR connector
Main (L+R) Test
5 Vrms, 75 ohms, unbalanced, BNC connector
Scope
2.5 Vrms auto-ranged, 75 ohms, unbalanced, BNC connector
Subcarrier Audio
+10 dBm, 600 ohms, balanced, XLR connector
Subcarrier Test
5 Vrms, 75 ohms, unbalanced, BNC connector
Subcarrier BPF
0.1414 Vrms @ 10.0%, 75 ohms, unbalanced, BNC connector
Interface
Serial
RS-232
Unit
Wizard Standard Interface
Remote Meter Outputs
Subcarrier Analog Modulation Meter
Open collector and relay closures for subcarrier presence and subcarrier peak modulation indicators.
Main (L+R) Specifications (20 Hz to 15 kHz)
Frequency Response
± 0.1 dB
Distortion (THD + Noise)
0.01%
SNR
80 dB
Subcarrier Specifications
(BPF BW = 16 kHz, Det BW = 8 kHz)
Frequency Response (20Hz to 8 kHz, 6 kHz Dev)
BPF In
+0.1, -1.75 dB
BPF Out
± 0.1 dB
Distortion (THD + N) @ 1 kHz, 6 kHz dev, 150 µsec
BPF In
0.25%
BPF Out
0.05%
SNR, 150 µsec de-emphasized
80 dB
Crosstalk
Sub to Main
80dB
Main to Sub
80dB
Stereo to Sub
80dB
Dimensions
1.75″H x 14.5″D x 19″W (1 EIA Rack Unit)
Power Requirements
17 Watts, 100-240VAC, 50-60 Hz
Net Weight
7 lbs.
Shipping Weight
11 lbs.
New in 2015 – 3 Year Factory Warrant to all Belar Products
