Patent GB-1275148-A (GB)
Title: Improvements in or relating to communication systems
Inventor: KAHN LEONARD RICHARD
IPC: H04B1/26
Filed: 1969-09-08
Abstract: 1275148 Combined radio receiver and transmitter systems; FM receivers L R KAHN 8 Sept 1969 [9 Sept 1968] 44242/69 Headings H3Q H3R and H4L A radio receiver includes means to sense the type of modulation of the received signals and to automatically switch a transmitter to transmit signals with the same type of modulation as that sensed by the receiver. In one arrangement, Figs. 1A, 1B, which distinguishes between an amplitude modulated carrier wave signal and a single sideband suppressed carrier signal, the receiver, Fig. 1A, operates in a similar manner to that disclosed in Specification 1,122,933. The signal from the 1.F. stage of the receiver is supplied to a peak detector 14 which develops a positive voltage in response to a single sideband signal and to an average detector 16 which provides a negative voltage in response to an amplitude modulated carrier, the output of the other detector in each case being much lower. The outputs of the detectors are supplied to each end of a potentiometer 22 which via circuits 26, 28 controls a relay MR which is de-energized (with contacts MR1, MR2 as shown) when the output of detector 16 is dominant and energized when that of detector 14 is dominant. Contact MR1 completes the circuit of either amplitude modulation transmitter control line X or single sideband transmitter control line Y and contact MR2 connects either a diode detector 34 for the amplitude modulated carrier wave or a product demodulator 44 for the single sideband signal. An A.G.C. circuit 52 provides conventional gain control for the I.F. stages, the control voltage from 52 also being supplied to a D.C. amplifier 60 which energizes a squelch relay SR when the signal strength is adequate, to supply an output signal via contact SR1 and from a power source 70 a "signal presence" signal on line Z via contact SR2. Assuming that an amplitude modulated carrier of adequate signal strength is being received, line X, Fig. 1B will be earthed and line Z energized so that relay RA is energized (as shown) and is held over contact RA1 and RB remains unenergized. Contacts RA2, RB2 act as an interlock ensuring that when one of the relays is energized it remains energized until the other relay becomes energized. Contact RA3 is opened when relay RA is energized, the corresponding contact RB3 of relay RB completing a circuit for the AM transmitter 96. When line Y is earthed and line Z is energized, relay RB is energized and RA is released so that the SSB transmitter 92 is brought into operation. In a modification, Fig. 2 (not shown), the outputs of an amplitude modulation generator and a single sideband generator are gated in accordance with the earthing of lines X or Y respectively and feed a common power amplifier. Receiver modifications.-A sideband filter and carrier filter feeding a pair of detectors connected to a potentiometer 22 as before determine which type of modulation (SS.B or amplitude modulated carrier) is being received and switch the transmitter accordingly, Fig. 3 (not shown), the signals being recovered by a common product demodulator. In a further arrangement using upper sideband, lower sideband or amplitude modulated carrier, the received signal is fed to an upper sideband filter and a lower sideband filter whose outputs are rectified and fed to a potentiometer as before controlling a threeposition relay. With normal amplitude modulation the outputs of the filters will be equal and opposite so that the relay remains inits intermediate position and the signal is supplied to diode detector. With an output from one or other of the filters the single sideband signal is supplied to an appropriate one of a pair of product demodulators. Corresponding control signals are supplied to the transmitter. In a receiver for differentiating between amplitude and frequency modulation signals, Fig. 5 (not shown), the received signals are supplied to a peak detector, more responsive to amplitude modulation signals, and an average detector, more responsive to frequency modulation signals, the outputs of the detectors being connected to a potentiometer as before, providing control signals to switch in the appropriate detector (AM or FM) and switch the transmitter to operate in the corresponding mode of modulation. A similar arrangement, Fig. 6 (not shown), distinguishes between S.S.B and F.M. In an alternative arrangement for differentiating between S.S.B. and amplitude modulated carirer, Fig. 7 (not shown), the incoming signal is limited at 200 and a detector 202 detects the phase or frequency modulation component present if the signal is S.S.B. to operate a relay for switching the transmitter accordingly and connecting in a product detector. If there is no output from this detector the relay is released and a conventional diode detector is connected.