GB1433588A - Arrangement for the signal/noise ratio of signals picked up by aerials comprising a plurality of elements - Google Patents

Abstract

1433588 Diversity reception COMPAGNIE INDUSTRIELLE DES TELECOMMUNICATIONS CIT-ALCATEL 30 July 1967 [13 Oct 1966] 25201/67 Heading H4L An arrangement for improving the signal/ noise ratio of signals occupying a narrow band and picked up by an aerial composed of a plurality of pick-up elements, comprises, as shown, two aerial elements I 1 , I 2 associated respectively, with channels 2 1 , 2 2 having delay networks 3 1 , 3 2 and band-pass filters 5 1 , 5 2 , the filter band width being equal to the narrow band of the useful signals S to be detected. The networks 3 1 , 3 2 ensure that two completely identical useful signals S are present at the two outputs 4 1 , 4 2 . The noise signals denoted by B 1 , B 2 , received by the aerial elements I 1 , I 2 , respectively, are of equal average power and have cross-correlation properties. The signals # 1 =S+B 1 and # 2 =S+B 2 are applied to an assembly E 1 to derive two voltages u, v, these voltages together with the aforementioned signals being applied to an assembly Eg to derive an output signal from an amplifier 76 having an inproved signal/noise ratio. The assembly E 1 comprises a member 14 for obtaining the difference B 1 -B 2 , a voltage squarer 15 and a low-pass filter 16 having a time constant of the same order of magnitude as the slow variations of the noises, the voltage u being taken from the filter output. The voltage u represents the average power of the difference of the noises B 1 , B 2 . The voltage v is taken from the output of a filter 13 having the same time constant as the filter 16. The input of filter 13 is connected to a multiplier 12 in which signals # 1 and # 2 are multiplied, the signal # 1 being phase shifted through in a phase converter 11, so that the voltage v is independent of signal S. The voltage v represents the average of the product of the noises B 1 , B 2 . The assembly Eg comprises adding devices 77, 79. In device 77 signals # 1 , # 2 are added whereas in device 79 signals # 1 <SP>1</SP>, # 2 <SP>1</SP> are added, the signal # 1 being phase shifted through in converter 78, to become signal # 1 <SP>1</SP> and signal # 2 being phase shifted through to become signal # 2 <SP>1</SP>. The outputs of devices 77, 79 are multiplied in multipliers 81, 82, respectively, by the voltages u, v. The outputs of the multipliers are supplied to an adder 83 feeding the amplifier 76 having its gain controlled by the voltage u.