GB1461393A - Pulse coded ocmmunication systems - Google Patents

Abstract

1461393 Determining significance of data bits NATIONAL RESEARCH DEVELOPMENT CORP 12 March 1974 [12 March 1973] 11787/73 Heading H4P In an apparatus for determining the significance of data bits in a two state data signal, especially of bit representations in a phase modulated signal in the presence of noise, a generator 16 e.g. a ring counter, provides a set of N pulse trains, a-h, starting one after another throughout an interval of t seconds, the pulses in each train occurring at t second intervals, being the same as the data bit duration. The pulse trains are applied to coincidence gates 8-15, the other input of each gate receiving a pulse m initiated at each transition in the data signal l. The output of each gate is coupled to a respective counter 17-24, each of which delivers a gating pulse at a predetermined count. Thus the counter associated with the pulse train most nearly in phase with the data signal transitions will rapidly run up to the predetermined count (e.g. 15) whereas the others which will only respond to odd, spurious transitions, will not. The gating pulse from the operated counter controls a respective latch 25-32 to hold open a respective gate 33-40. This gate receives one of the pulse trains, a-h, occurring half a bit (t/2) after the pulses applied to the counter controlling the latch. The sampling output from the selected gate 33-40 is sampled to the main logic circuit 41 to determine the appropriate sampling instants for the data signal. The arrangement is for use in analysing data signals derived from a phase comparator 5 in which a required phase shift keyed signal transmitted by a responder 1 in a vehicle in response to an interrogating signal from a generator 3 and radiating loop 2 is compared with the locally generated interrogating signal.