STATISTICAL DESIGN AND PERFORMANCE OF HIGH-SENSITIVITY FREQUENCY-FEEDBACK RECEIVERS
AEROSPACE CORP EL SEGUNDO CA
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A design theory and an analytical threshold determination are presented for a high-sensitivity frequency-feedback receiver. Current interest in high-sensitivity receivers for frequency modulation is centered around two implementations of the device phase-lock and frequency-feedback. The derivation of quasi-linear model for the frequency-feedback receiver, for the situation of Gaussian signals and noise, is presented. A statistical optimization is then performed giving the loop transfer function and threshold performance for a maximum sensitivity receiver. The design theory is based on a single threshold concept discarding the previous twin threshold approach. It is shown that in an optimum design the modulation error is less than 1 rad. This allows the use of a narrow-band i-f filter and obviates the need to consider threshold characteristics of the discriminator within the loop. A significant result of this analysis is that al though the quasi-linear receiver models differ in detail, threshold for a maximum sensitivity FM feedback and phase-lock receiver is identical. It was found that in FM feedback, as previously determined by Develet for the phase-lock reveiver, threshold occurs at 10 log 10 e 4.34 db above the ultimate limit determined by information theory arguments. This 4.34 db degradation is ind pendent of modulation index.
- Radio Communications