Original Publication Date: 1980-Aug-01
Included in the Prior Art Database: 2001-Oct-10
It was desired to limit the bandwidth of an FM signal with little loss in performance and with minimal additional circuitry. The solution was to impose AM modulation on the FM signal in such a way as to make the resulting RF spectrum more bandlimited than had no AM been added at all. This would require no changes in the PM receiver as the receiver would strip off the AM by limiting the received signal, and hence would only detect the FM component as before. The scheme would also not affect transmitter design as the highly efficient class-C power amplifier could still be used, with the AM being added on at the last stage as is commonly done in transmitters used in the Citizens' Band.