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SCMA-1 photo



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.

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.



   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

   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%

   Composite                                    1.0 - 2.0 Vrms (2.8V - 5.7V P-P),
                                                100 k ohms, unbalanced, BNC Connector

   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


   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

   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.

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© Copyright 2000 Belar Electronics Laboratory, Inc. All rights reserved. Specifications subject to change without prior notice.

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