Optimum Subcarrier Deviation for PCM/FM+FM/FM Systems using IRIG Constant Bandwidth Channels
AffiliationNew Mexico State University
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AbstractA typical PCM/FM system is designed for a peak to peak carrier deviation of 0.7 times the bit rate of the PCM data. This value of PCM data deviation has been shown to be optimum for both PCM/FM  and PCM/FM+FM/FM  systems. However, the optimum deviation of the carrier by the FM subcarrier for a PCM/FM+FM/FM system is dependent upon the specific subcarrier type and required subcarrier signal to noise ratio at the receiver output. This paper introduces a simple method to calculate the optimum deviation of the carrier by FM subcarriers for a PCM/FM+FM/FM system. The method developed is used to calculate the optimum value of subcarrier deviation for two sample PCM/FM+FM/FM systems when IRIG constant bandwidth channels are used as FM subcarriers. The calculated optimum values of FM subcarrier deviation of the carrier, subcarrier mod index, are utilized in a companion paper to study the performance of PCM/FM+FM/FM systems . The work presented herein can be extended to calculate the optimum deviation of the carrier by FM subcarriers for any PCM/FM+FM/FM system.
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