Analysis of FM demodulator output noise with applications to the space lift range system

This paper presents an analysis of the performance of the FM demodulator when the input signal-to-noise power ratio (SNR) at the demodulator input is below the FM threshold. The analysis is based on the probability distribution of the FM demodulator output noise derived by the author of this paper. Such a distribution is applicable to the complete range of the SNR at the demodulator input. However, due to the analytic complexity of the problem, the derivation does not take into account the effect of the post demodulation video filter. For the FM telemetry schemes, earlier simulation studies have shown that the best performance is achieved when the video filter bandwidth is of the order of the IF bandwidth. In such cases the impact of the video filter is expected to be relatively small. However, in some FM command link applications considered in the paper, the bandwidth of the post demodulation low pass filter is relatively small and thus the result of the earlier analysis can´t be applied directly. This paper presents a novel manner in which the previous analysis can be extended to this case in a relatively simple manner. The results obtained by this analysis have also been validated by simulations