Patent GB-1404590-A (GB)
Title: Radio signalling equipment
IPC: H04B7/01
Filed: 1971-12-17
Abstract: 1404590 Radio signalling; radar DEFENCE SECRETARY OF STATE FOR 15 Dec 1972 [17 Dec 1971] 58827/71 Headings H4D and H4L Radio signalling equipment including receiver apparatus for receiving signals comprising a variable-frequency carrier-wave phase-modulated by binary signals, incorporates first and second signal paths having a common input connected to receive the signals, delay means connected in one signal path for delaying the signals relative to those in the other path by an integral multiple of the bit-duration of a signal, and mixer means connected to receive signals from both paths for deriving an auto-correlation signal the magnitude of which is dependent on the relative phases of the signals received thereby. The equipment may be used as radar range finding or proximity-evaluing equipment or to form digital telecommunications equipment. Radar.-A pseudo - random digital pulse stream from a code generator 1 is applied to a PSKM 2 to control the phase of a microwave carrier generated by oscillator 3. The bi-phase modulated carrier signal it transmitted from aerial 4 towards a target 16. The reflected signal received by aerial 6 passes through IF stages 5 to the local oscillator input of mixer 7 and to an acoustic delay line 8 prior to passing to the signal input of the mixer 7. The latter autocorrelates the received signal with a delayed self-replica to produce a positive output when the inputs are in phase and a negative output when the inputs are out of phase, thereby providing an ou put pulse stream. The latter passes to the local oscillator input of a further mixer 9 whose signal input receives a stream of pulses derived from the generator 1, exclusive OR-gate 13 and shift-register 15. This stream corresponds to the stream from the mixer 7 though the latter is delayed by the two-way propagation time t 1  and slightly modified by the Doppler effect. The output of the shiftregister 15 it taken from a point such that the output stream is delayed by time t 2  relative to its input. The streams applied to mixer 9 thus match when t 1  = t 2  to produce a significant output. As the target 16 comes within a selected range, the output from mixer 9 changes from one D.C. level (corresponding to lack of significant cross-correlation) to a second D.C. level, and the integrated and filtered signal, if exeeding a threshold level in a circuit 12, can be used to actuate an alarm or fire a weapon. In a modification (not shown), the incoming signals are fed to both ends of an acoustic delay line and an output taken from a transducer located nearer to one end of the line than the other so that the response of the transducer depends on the relative phase of its two inputs. The transmitter and receiver aerials may be combined and an interleaving switch provided. Digital telecommunications.-The apparatus is basically similar to that for use as a radar, but the OR-gate 13, its associated delay 14 and shift-register 15 are omitted; further, the code generator 1 is replaced by a source of digital signals to be transmitted. In such a system, the the output signals from mixer 7 will differ from, though be related to the transmitted signals. In order that the signals derived by the mixer 7 shall be the signals which it is desired to convey, the transmitter includes a J-K flip-flop with its J and K inputs connected to the source of signals for transmission. The flip-flop produces signals related to the signals to be conveyed in such a way that correlation in the mixer 7 will regenerate the signals of the source.