Single oscillator microwave transceiver

• US 3,935,533 A
• Filed: 08/29/1974
• Issued: 01/27/1976
• Est. Priority Date: 03/02/1973
• Status: Expired due to Term

• Current Assignee: United Technologies Corporation (Raytheon Technologies Corporation d/b/a RTX)
• Original Assignee: United Technologies Corporation (Raytheon Technologies Corporation d/b/a RTX)
• Inventors: Amoroso, Salvatore Jr.
• Primary Examiner(s): Safourek, Benedict V.
• Application Number:
  US05/501,721
• Time in Patent Office: 516 Days
• Field of Search: 325/17-20, 325/23, 325/24, 325/25, 325/430, 325/438, 343/175, 343/179, 343/180, 178/58 R, 178/59, 178/60, 179/170 R, 179/170 NC, 179/170 T
• US Class Current: 455/75
• CPC Class Codes: H04B 1/408 the transmitter oscillator frequency being identical to the receiver local oscillator frequency
• CPC Class Codes: H04B 1/50 using different frequencies for the two directions of communication

Abstract

A voltage variable oscillator feeds an FM modulated signal to be transmitted to an orthomode transducer connected to a dual polarization antenna, another port of the orthomode transducer feeding received FM signals to a single ended mixer, the output of which is passed through an FM receiver. The orthomode transducer leaks a portion of the transmitted wave to the single ended mixer, for use in lieu of a local oscillator, thereby limiting the requirements to a single microwave oscillator. The output of the FM receiver is applied to a cancellation circuit where the transmitter modulation is cancelled from the FM receiver output in response to delayed transmitter input signals. The output of the cancellation circuit comprises the receiver output, and is used as the signal input of a phase sensitive demodulator, the phase reference input of which is the delayed transmitter modulation, the phase sensitive demodulator controlling the gain of a variable gain amplifier so as to provide complete closed loop automatic gain control, limiting the frequency excursion of the oscillator in such a fashion as to permit complete cancellation of the transmitter input modulation from the receiver output modulation, despite any variations in circuit scale factor. In a system employing more than one transceiver having the same receiver IF frequency, an automatic frequency control loop is provided in one of the transceivers, and nominal or stabilized frequency control is applied in the other, whereby one frequency is slave to the other separated by the IF frequency; in addition, means are provided in conjunction with the cancellation circut to accommodate the opposite polarity of the discriminator output in two different transceivers communicating with one another resulting from discrimination of opposite sidebands.

Claims

1. A single oscillator microwave transceiver comprising:

a single microwave oscillator having a frequency-controlling voltage input;

an FM receiver;

antenna means for transmitting and receiving microwave energy;

means for coupling energy from said oscillator to said antenna means for transmission thereby, and for simultaneously coupling energy received at said antenna means and a small portion of the energy of said oscillator in mixed fashion to the input of said FM receiver;

an AFC circuit connected to the output of said FM receiver;

means for providing a substantially DC voltage suitable for controlling the carrier frequency of said microwave oscillator;

summing means, the output of said summing means being connected to said frequency-controlling voltage input of said microwave oscillator;

input means for applying transmitter input modulation to one input of said summing means; and

first selectively operable means for connecting said AFC circuit or carrier voltage means to a second input of said summing means, alternatively, whereby said microwave oscillator provides a carrier frequency selectively determined by said AFC circuit or by said carrier voltage means, which is frequency modulated in accordance with said transmitter input modulation;

wherein said input means includes a variable gain amplifier having a signal input and a gain control input, said signal input being connected to transmitter input modulation, the output of said variable gain amplifier being connected to the first input of said summing means;

delay means responsive to transmitter input modulation for providindg delayed transmitter input modulation which is delayed by a period of time substantially equal to the circuit signal propagation time from the input of said variable gain amplifier through said FM receiver;

second selectively operable means responsive to the output of said FM receiver and to the output of said delay means for selectively combining said delayed transmitter input modulation with the output of said FM receiver in a voltage polarity relationship to provide a receiver output signal having transmitter input modulation substantially cancelled therefrom; and

means responsive to said receiver output signal and to said delayed transmitter input modulation for providing a gain control signal to the gain control input of said variable gain amplifier, said gain control signal adjusting the gain of said variable gain amplifier so that the magnitude of transmitter input modulation included in the output of said FM receiver is adjusted with respect to the magnitude of delayed transmitter input modulation provided by said delay unit so that the transmitter input modulation in said receiver output signal is substantially nulled to zero.

2. A transceiver according to claim 1 wherein both of said selectively operable means comprise manually operable switches.

3. A transceiver according to claim 2 wherein said manually operable switches are ganged together for concurrent operation.

4. A communication system comprising a pair of transceivers according to claim 3, said ganged switches in a first one of said transmitters being adjusted to connect said AFC circuit to said summing means and to provide a first voltage polarity relationship, said ganged switches in a second one of said transceivers being adjusted to connect said carrier voltage means to said summing means and to provide a second voltage polarity relationship opposite to said first voltage polarity relationship.

5. A single oscillator microwave transceiver comprising, in combination with a single microwave oscillator:

an FM receiver;

antenna means for transmitting and receiving microwave energy;

means for coupling energy from said oscillator to said antenna means for transmission thereby, and for simultaneously coupling energy received at said antenna means and a small portion of the energy of said oscillator in mixed fashion to the input of said FM receiver;

means including a variable gain amplifier responsive to transmitter input modulation for controlling the frequency of oscillation of said microwave oscillator;

cancellation means responsive to the output of said FM receiver and to transmitter input modulation for cancelling similar modulation from the output of said FM receiver and for thereby providing a receiver output signal; and

gain control means responsive to said cancellation means for controlling the gain of said variable gain amplifier, in a manner to null the transmitter input modulation in the receiver output signal to zero.

6. A transceiver according to claim 5 wherein said cancellation means includes means for delaying said transmitter modulation to be in phase with that coupled by said coupling means through said FM receiver, and means for alternatively adding or subtracting said delayed transmitter input modulation and said FM receiver output in dependence upon the polarity of said FM receiver output.

7. A transceiver according to claim 6 wherein said variable gain amplifier has a gain controlling input, and said gain control means comprises a phase sensitive demodulator having its phase reference input connected to the output of said delaying means, its signal input connected for response to the receiver output signal of said cancellation means, and its output connected to said gain controlling input of said variable gain amplifier.

8. A single oscillator microwave transceiver comprising:

a single microwave oscillator having a frequency-controlling voltage input;

an FM receiver;

antenna means for transmitting and receiving microwave energy;

means for coupling energy from said oscillator to said antenna means for transmission thereby, and for simultaneously coupling energy received at said antenna means and a small portion of the energy of said oscillator in mixed fashion to the input of said FM receiver;

a variable gain amplifier having a signal input and a gain control input, said signal input being connected to transmitter input modulation, the output of said variable gain amplifier being connected to said frequency-controlling voltage input of said oscillator;

delay means responsive to transmitter input modulation for providing delayed transmitter input modulation which is delayed by a period of time substantially equal to the signal propagation time from the input of said variable gain amplifier through said FM receiver;

cancel means responsive to the output of said FM receiver and to the output of said delay means for selectively combining said delayed transmitter input modulation with the output of said FM receiver in voltage combining relationship to provide a receiver output signal having transmitter input modulation substantially cancelled therefrom; and

means responsive to said receiver output signal and to said delayed transmitter input modulation for providing a gain control signal to the gain control input of said variable gain amplifier, said gain control signal adjusting the gain of said variable gain amplifier so that the magnitude of transmitter input modulation included in the output of said FM receiver is adjusted with respect to the magnitude of delayed transmitter input video provided by said delay unit so that the transmitter input modulation in said receiver output signal is substantially nulled to zero.

9. A communication system comprising a pair of transceivers according to claim 8, said cancel means in a first one of said transceivers being adjusted to provide a voltage combining relationship opposite to that of a second one of said transceivers.

10. A duplex transceiver system including a pair of transceivers settable for operation with one in a master mode and one in a slave mode, each of said transceivers comprising:

a single, voltage-tunable, solid state microwave oscillator having means for providing a frequency-controlling voltage input thereto;

an FM receiver having the same IF frequency in both of said transceivers and providing a conventional AFC signal;

antenna means for transmitting and receiving microwave energy;

means for coupling energy from said oscillator to said antenna means for transmission thereby, and for simultaneously coupling energy received at said antenna means and a small portion of the energy of said oscillator in mixed fashion to the input of said FM receiver;

means providing a carrier frequency designating signal;

means in each of said transceivers selectively operable in response to said frequency designating signal or in response to said AFC signal, alternatively, for providing a carrier frequency controlling voltage to the frequency-controlling voltage input means of said oscillator so as to control the carrier frequency of the related transceiver, whereby said transceivers, when operating in a duplex pair with one in response to said carrier frequency designating signal and one in response to said AFC signal, will each provide its own carrier frequency offset from the carrier frequency of the other by said common IF frequency, whereby the FM receivers and said transceivers provide FM receiver outputs discriminated from mutually opposite sidebands;

input means providing transmitter input modulation to said frequency controlling voltage input means of said oscillator;

delay means responsive to the transmitter input modulation of said input means for providing delayed transmitter input modulation which is delayed by a period of time substantially equal to the circuit signal propagation time from said input means through said FM receiver; and

cancel means responsive to the output of said FM receiver and to the output of said delay means for combining said delayed transmitter input modulation with the output of said FM receiver, including means for controlling the polarity of the transmitter input modulation of each transceiver passed through the related FM receiver of that transceiver so as to provide it in a polarity opposite to that provided by the related delay means, said means being settable for opposite polarities in the respective transceivers of a pair, so as to cancel said transmitter input modulation from the output of said FM receiver to provide a transceiver output signal.

11. A transceiver system according to claim 10 wherein said input means includes a variable gain amplifier having a signal input and a gain control input, said signal input being connected to transmitter input modulation, the output of said variable gain amplifier being connected to said frequency controlling voltage input of said oscillator;

and

further comprising AGC means responsive to said transceiver output signal and to said delayed transmitter input modulation for providing a gain control signal to the gain control input of said variable gain amplifier, said gain control signal adjusting the gain of said variable gain amplifier so that the magnitude of transmitter input modulation included in the output of said FM receiver is adjusted with respect to the magnitude of delayed transmitter input modulation provided by said delay unit so that the transmitter input modulation in said receiver output signal is substantially nulled to zero.

12. A transceiver system according to claim 11 wherein said AGC means comprises a synchronous demodulator having a signal input connected to the transceiver output signal of said cancel means and its reference input connected to said delay means, its output connected to said gain control input of said variable gain amplifier.

13. A transceiver system according to claim 11 wherein said cancel means includes means for selectively switching the polarity of transmitter input modulation applied to said frequency-controlling input means of said oscillator.

14. A transceiver system according to claim 11 wherein said cancel means includes means for switching the polarity of one of the input signals to said cancel means at the input thereof.