The Belar SCMA-1 FM modulation monitor and digital analyser is a precision DSP-based SCA monitor designed to work in conjunction with Belar’s FMMA-1 or FMM-2 modulation monitor or other wideband composite source.
The SCMA-1 digitises the composite and decodes the selected subcarrier signal using digital signal processing techniques. Unlike an analogue design, a DSP-based design is not subject to variations due to temperature, component ageing 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 allows the user to optimise the cut-off frequencies of the subcarrier BPF and detector LPF 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 synthesised from a common system clock.
The SCMA-1 implements all of its measurement and metering functions using DSP processing. Therefore, the calibration of the SCMA-1 does not depend on any adjustable circuit components or their tolerances. This ensures that the calibration of the unit remains stable over time. By digitising the measurements, the user can directly view the modulation peaks, injections and dB readings. As an added benefit, all readings can be viewed remotely using an IBM compatible personal computer.
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