GB623219A - Means and method for relaying frequency modulated signals - Google Patents

Abstract

623,219. Radio signalling. ARMSTRONG, E. H. Jan. 11, 1947, No. 994. Convention date, Jan. 12, 1940. Drawings to Specification. [Class 40 (v)] At a relaying station the received F.M. wave is given a desired small increment or decrement of frequency by first reducing the received wave to an intermediate frequency by heterodyning with a local crystal oscillator, then applying the desired increment or decrement, and finally raising the frequency by the same local oscillator. The local oscillation may be multiplied in frequency before being used for the frequency-reducing stage, and the subsequent frequency-raising stage may be performed by harmonics of the local oscillator applied in successive steps. Suitable filters and amplifiers may be employed at the various stages, and a limiter may be used in the intermediate frequency stage. The receiving and transmitting aerials may be some distance apart, with some of the frequency-changing stages adjacent to each aerial. Any drift in the frequency of the main local oscillator is self-cancelling; and the oscillator which applies the small increment or decrement is of such low frequency that any variation therein is insignificant in its influence on the outgoing carrier frequency. Specification 426,228 is referred to.