FM HETERODYNE TRANSMITTER

• US 3,789,302 A
• Filed: 03/31/1972
• Issued: 01/29/1974
• Est. Priority Date: 03/31/1972
• Status: Expired due to Term

• Current Assignee: Fred P. Collins, Richard H. Rearwin
• Original Assignee: Fred P. Collins, Richard H. Rearwin
• Inventors: Rearwin, Richard H., Collins, Fred P.
• Primary Examiner(s): Safourek, Benedict V.
• Application Number:
  US05/240,217
• Time in Patent Office: 669 Days
• Field of Search: 325/125,126,148,159,184,7,9,11,153 331/18,25 332/16R,19 330/124,125,126
• US Class Current: 455/111
• CPC Class Codes: H03L 7/06 using a reference signal applied to a frequency- or phase-locked loop

Abstract

An FM heterodyne transmitter is disclosed useful, for example, in a microwave relay link, using all solid-state components throughout. The transmitter includes an RF amplifier which generates locally a signal having the same frequency as the signal carrier and a phase comparator which accepts both the local and the received signals and provides an error signal responsive to a phase difference between them. The error signal is used in a feedback amplifier loop to correct the local oscillator frequency in the direction which tends to negate the error signal.

Claims

1. In an FM heterodyne transmitter, RF amplifier means comprising input means (to provide an) for a modulated RF signal at a specified carrier frequency, voltage-controlled local oscillator means to provide a signal at a frequency which is a specified fraction of said carrier frequency, first frequencymultiplier means arranged to accept a sample of said local oscillator signal and to provide in response thereto a first output signal having the same frequency as said carrier frequency, phase-comparator means arranged to accept said RF signal and said first output signal and to provide (an) a DC error signal responsive in magnitude to a phase difference between them and an AC signal which substantially repeats the modulation information of said RF signal, error signal feedbackamplifier means arranged to receive said error signal and to provide in response thereto a controlling voltage to said local oscillator whereby to cause said local oscillator to oscillate at a frequency tending to negate said error signal, local oscillator signal amplifier means coupled to said local oscillator to receive local oscillator output signal and amplify same, and second frequency-multiplier means arranged to receive amplified local oscillator signal from said amplifier and to provide in response thereto a second output signal having an output carrier frequency which may be the same frequency as said input carrier frequency, and substantially repeating the frequency deviations of said input modulated RF signal.

2. Amplifier means according to claim 1 in which said error feedback means comprises two branches, a first branch having low-pass filter properties for providing essentially a DC voltage to tune said local oscillator means, a second branch having high-pass filter properties for providing an AC voltage having modulation information to said local oscillator, time delay of modulation information through said second branch being on the order of two nanoseconds.

3. Amplifier means according to claim 1 in which said local oscillator comprises a cavity resonator and a voltage-variable capacitance semiconductor device for adjusting the resonance frequency responsive to a DC voltage applied to said semiconductor device, and said error signal comprises a DC voltage, and means coupling said DC voltage to said semiconductor device.

4. Amplifier means according to claim 1 in which said local oscillator includes sampling means for providing a low level signal to said first frequency multiplier means.

5. Amplifier means according to claim 3 in which said resonator is a coaxial resonator having an inner conductor along which a voltage standing wave pattern is developed during oscillation, and including a first output coupling member located relative to said conductor for extracting a signal at a first level near the anti-node peak of said pattern for amplification and output, and a second output coupling member located relative to said conductor for extracting said sample at a second lower level which is a small fraction of said first level.

6. Amplifier means according to claim 5 including a resistive diode connected at one side to said second output coupling member and at the other side to a filter dimensioned to pass a harmonic of the resonance frequency of said cavity.

7. Amplifier means according to claim 6 in which said filter is a waveguide section attached to said resonator, and coupled thereto via a common aperture.

8. Amplifier means according to claim 1 in which a directional coupler is disposed between said local oscillator and said local oscillator signal amplifier means, for providing a sample of said local oscillator signal to said first frequency multiplier means.

9. Amplifier means according to claim 1 in which said first frequency multiplier means exhibits time delay on the order of two nanoseconds.

10. Amplifier means according to claim 2 in whIch said first frequency multiplier means exhibits time delay not greater than about two nanoseconds.

11. Amplifier means according to claim 2 in which said first branch includes phase comparator means providing an output voltage which is zero when the phase difference between said RF signal and said first output signal is zero and which in the presence of a phase difference shifts an amount proportional to the difference but not greater than a fraction of a volt away from zero in a sense dependent on the direction of said difference, and an essentially DC amplifier having input means to compare said phase comparator output voltage with a reference for amplifying said amount while retaining the sense information.

12. Amplifier means according to claim 11 in which said DC amplifier has an output circuit that provides a nominal error-signal output voltage having an established magnitude representing the case of zero phase difference, and said amplified amount is added to said nominal voltage, the magnitude of said amplified amount being smaller in all cases then said established magnitude.