THRESHOLD COMPARISON OF PHASE-LOCK, FREQUENCY-LOCK, AND MAXIMUM- LIKELIHOOD TYPES OF FM DISCRIMINATORS
LOCKHEED MISSILES AND SPACE CO INC SUNNYVALE CA
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IN MAKING A COMPARISON OF DEMODULATION TECHNIQUES FOR FM signals, one of the most important criteria for evaluation is the threshold input signal-to- noise ratio SNR. It is at this value of input SNR that the output SNR begins to decrease, substantially more rapidly than a simple proportionality to the input SNR. A consistent derivation is presented of the threshold SNR for several major types of FM discriminators, namely, the phase-lock discriminator, the frequency-lock discriminator FM discriminator with negative feedback, and the maximum-likelihood a posteriori, most probable computer. This last discriminator is of interest mainly because its operation provides a bound on the performance of other types. The operation of the discriminators in the presence of gaussian interfering noise is described, and the causes of threshold are investigated.
- Electrical and Electronic Equipment