Narrow bandwidth radio receiver having means to position an rf signal within a steep sided passband filter

Claim 2

A highly stable narrow bandwidth receiver comprising 1 means responsive to receiver radiofrequency signals for producing an amplified first intermediate frequency signal representative thereof, a first mixer circuit having first and second inputs with the first input coupled to the intermediate frequency signal, a narrow bandwidth amplifier having a sharply defined passband and having its input coupled to the output of the first mixer circuit, a variable beat frequency oscillator source for passband tuning, a detector coupled to the output of the narrow bandwidth amplifier and the beat frequency oscillator source for producing a utilization signal, a main tuning, variable frequency local oscillator course, a second mixer having first and second inputs and a beat frequency output, the first input being coupled to the main tuning, variable frequency local oscillator source and the second input being coupled to the passing tuning, beat frequency oscillator source, and the beat frequency output coupled to the second input of the first mixer, whereby changes in the output of the variable beat frequency oscillator alter the position of the radiofrequency signal within the passband without altering the tuning frequency of the receiver.

Claim 3

The device as recited in claim 1 wherein the narrow bandwidth amplifier includes a crystal lattice filter.

Claim 4

In a highly stable radiofrequency receiver wherein information-carrying radiofrequency signals are converted with the use of an injection frequency oscillator to an intermediate frequency signal which, after passage through a very narrow sharply defined, bandwidth filter, is demodulated in a product detector with a variable beat frequency oscillator coupled thereto and including a first mixer to apply the intermediate frequency signal to said detector, the improvement comprising an electronic automatic frequency compensating feedback loop including a first variable frequency oscillator source, means including a second mixer circuit having a first input coupled to the variable frequency oscillator signal source and a second input coupled to the variable beat frequency oscillator, the output thereof providing the desired input frequency signal to said first mixer, with the conversion of the radiofrequency information signals and the mixer circuit being selected to provide a frequency change in the intermediate frequency signal corresponding to variations in the beat frequency oscillator, the beat frequency oscillator being variable for selectively positioning the intermediate frequency signal within the passband of the filter without alteration of the tuning frequency of the radio receiver.

Claim 5

In a highly stable radiofrequency receiver wherein information-carrying radiofrequency signals are converted with the use of an injection frequency oscillator to an intermediate frequency signal which, after passage through a very narrow sharply defined, bandwidth filter, is demodulated in a product detector with a variable beat frequency oscillator coupled thereto and including a first mixer to apply the intermediate frequency signal to said detector, the improvement comprising an electronic automatic frequency compensating feedback loop including a first variable frequency oscillator source, means including a second mixer circuit having a first input coupled to the variable frequency oscillator signal source and a second input coupled to the variable beat frequency oscillator, the output thereof providing the desired input frequency signal to said first mixer, with the conversion of the radiofrequency information signals and the mixer circuit being selected to provide a frequency change in the intermediate frequency signal corresponding to variations in the beat frequency oscillator, the beat frequency oscillator being variable for selectively positioning the intermediate frequency signal within the passband of the filter without alteration of the tuning frequency of the radio receiver.

Claim 6

The device as recited in claim 3 wherein the feedback loop further includes a second fine tuning local oscillator source, a third mixer circuit having a first input coupled to the second local oscillator source and having a second input coupled to the beat frequency oscillator and having a converter output coupled to the second input of the second mixer circuit said first variable and second fine tuning oscillators being variable in frequency to provide respectively coarse and fine tuning of the radiofrequency receiver.