Double superheterodyne receiver with independent frequency calibration of two local oscillators

Claim 1

A superheterodyne receiver performing a plurality of frequency converting operations and having at least a first mixer connected to receive a signal having a desired frequency and to a first local oscillator to produce a first intermediate-frequency signal, and a second mixer connected to an output of the first mixer and to a second local oscillator to produce a second intermediate-frequency signal, said receiver comprising: a phase-locked loop for implementing said first local oscillator; and means excluding a phase-locked loop and including a variable frequency oscillator for implementing said second local oscillator; control means connected to control said first and said second local oscillators; wherein said received signal is supplied to said first mixer the output of which is varied by varying at least a frequency generated by said first local oscillator in response to a control signal from said control means, a frequency of said first oscillator is frequency calibrated by said control means to a frequency of the first intermediate-frequency signal, the second intermediate-frequency signal supplied by said second mixer is frequency-converted by a beat-frequency oscillator signal to a signal having a frequency of voice band, and a frequency of said second local oscillator is frequency calibrated independently of said first local oscillator by said control means, whereby a signal resulting from the frequency conversion in said second mixer is set to a specified frequency.