Tweet elimination, or reduction, in superheterodyne receivers

Claim 1

In a superheterodyne receiver, having a predetermined intermediate frequency (IF) band and a nominal IF, apparatus for preventing or reducing an undesirable frequency relation which may exist between a received radio frequency (RF) signal and the resulting actual IF signal, comprising: first means for supplying a local oscillator (LO) signal at selected different nominal frequencies and whose specific actual frequency can be controlled, and for also supplying a second signal representative of the nominal IF of said receiver, said LO signal and said second signal being derived from a single master oscillator; second means for supplying a received RF signal; third means for combining said RF signal and said LO signal to develop an IF signal within said IF band; fourth means, responsive to said second signal and to said IF signal, for developing a control signal representative of the existance of said undesirable frequency relation between said RF signal and said IF signal; and means for applying said control signal to said first means, for controlling the frequency of said master oscillator, and therefore said LO signal, so as to prevent or reduce said undesirable frequency relation.