GB1306859A - Communication receivers - Google Patents

Abstract

1306859 Radio receiving circuits; interference suppression LICENTIA PATENT-VERWALTUNGS-GmbH 5 June 1970 [20 June 1969] 27157/70 Headings H3Q and H4L A communication receiver includes in its signal path a comb filter operative for selecting signals at required transmitter frequencies. In an embodiment, the aerial 1, Fig. 1, is coupled to the receiver 6 via a bandpass filter 2 covering the whole of the band to be received, followed by a comb filter 4: the frequency spacing between a suppression point and a pass-band centre point of the comb filter is made equal to the frequency spacing of stations in the band, so that alternate stations are rejected. The comb filter may comprise a delay line in the signal path to whose output is added a signal direct from the input (Figs. 2(a), 2(b), not shown) or the signal may be subtracted (Figs. 3(a), 3(b), not shown). In a further embodiment the output of delay line 8, Fig. 4, is fed to an adder 9 and to a subtraction circuit 14, to both of which signal is also applied directly and a switch 17 enables alternative sets of stations to be selected. The comb filter, which may employ a mechanical resonator, may alternatively be placed in an I.F. circuit, and the receiver may comprise a double superheterodyne.