Belar SCMA-1 Precision Digital FM SCA Modulation Analyzer

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Belar SCMA-1

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 

Product Resources

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