Power-Bandwidth Trade-offs for Feedback FM Systems

A Comparison with Pulse-Code-Modulation

by Edward Bedrosian


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A discussion of the use of negative feedback in FM (frequency-modulation) receivers to lower the signal level required for a given quality of performance. This technique could be important in the design of communications satellites because it minimizes the amount of transmitter power that must be placed in orbit. The author shows that the use of large amounts of feedback can reduce the transmitter power required by about 8 db (compared with a conventional FM system designed to minimize transmitter power) and by about 5 db (compared with a pulse-code-modulation system of comparable performance). The penalty paid for this improvement is an increase in the bandwidth occupied: The feedback system requires a radio channel about twice as wide as that used by either of the other two systems

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