Transmitter/receiver for single channel duplex communication system

• US 4,238,850 A
• Filed: 11/29/1978
• Issued: 12/09/1980
• Est. Priority Date: 12/01/1977
• Status: Expired due to Term

• Current Assignee: STC PLC (f/k/a Standard Telephones and Cables)
• Original Assignee: International Standard Electric Corporation (ITT, Inc.)
• Inventors: Vance, Ian A. W.
• Primary Examiner(s): Olms, Douglas W.
• Application Number:
  US05/964,764
• Time in Patent Office: 741 Days
• Field of Search: 179/15 R, 179/15 BC, 179/2 EA, 178/59, 325/60, 325/47, 343/176, 343/180, 343/205, 343/207, 343/208, 370/24, 370/27, 370/32, 370/38, 370/39, 370/20
• US Class Current: 370/278
• CPC Class Codes: H04B 1/54 using the same frequency for two directions of communication H04B1/44 takes precedence

Abstract

A transmitter receiver which can be used for a cordless telephone using radio communication. The receiver produces direct conversion from the radio frequency. Local oscillator frequency is modulated by an audio signal to be sent, the modulated signals being passed through a dual splitting and combining network. The splitting network has directional properties for duplex operation. The receiver processes the signals through a differential amplifier to cancel unwanted signals.

Claims

1. A transmitter/receiver for a single channel duplex communication system including a local oscillator for generating a frequency which is the center frequency of the single channel signals, means for frequency modulating the frequency output of said local oscillator with a first audio frequency signal, first and second means for directionally combining the local oscillator output in phase quadrature with audio frequency modulated signals received from the single channel, whereby a major portion of the local oscillator output is transmitted from each combining means to the single channel and a minor portion of the local oscillator output together with the received signals is applied from each combining means to first and second mixing means respectively, means for low pass filtering each of the outputs of the first and second mixing means, means for amplifying each of the outputs of the low pass filtering means to a constant level, separate means for differentiating each of the outputs of the amplifying means, means for multiplying the output of each differentiating means with the input of another differentiating means to provide (a) demodulated second audio frequency signal, signal means for subtracting a proportion of the first audio frequency signal from the demodulated second signal and means for feeding the output of the local oscillator in combination with a phase quadrature output of the local oscillator through said combining means to an aerial via which signals which are frequency-modulated with the second audio frequency are received.

2. A transmitter/receiver according to claim 1, in which the combining means between the oscillator and the first and second mixing means are hybrid circuits which have isolation between the ports to the local oscillator (ports) and ports to the output (ports) of the transmitter/receiver.

3. A transmitter/receiver according to claim 1, in which the combining means between the oscillator and the first and second mixing means are circulators.

4. A transmitter/receiver according to claim 1, in which the combining means between the oscillator and the first and second mixing means are resistive splitting networks.