Belar, Precision Digital FM SCA Modulation Analyser
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.