Showing papers on "Co-channel interference published in 1974"

Co-channel interference suppression apparatus

Abstract: The present invention refers to apparatus intended to suppress multiple co-channel interference and reflections from desired stations. The outputs of a two antenna array, which has been directed at the desired station, are fed to a sum-and-difference hybrid. The outputs of the hybrid are adjusted in amplitude and phase and combined to null the interference signal. The phase shift required for nulling is either ±90°. The sign is determined by the side of the array on which the interference source is located. The phase relation is true regardless of the exact location of the interference, requiring only a single adjustment in amplitude to null the source of interference. By adding a third antenna to the array and a phase detector to the system, a signal representing the direction of the source of interference is produced and is used to introduce either a ±90° phase shift and to set the required attenuation automatically cancelling the interference signal even if the interference signal source moves as effectively occurs with the resultant of multiple sources of interference.

Reduction of mush-area distortion in common-frequency m.f. transmitter networks

Abstract: The present crowding of the medium-wave band has made it necessary for several transmitters which broadcast the same programme to operate at a common carrier frequency. Reception is impaired by ground-wave interference between pairs of such transmitters in regions where the ratio of their field strengths is less than about 10 dB. At night, mutual interference is caused by sky-wave signals from other transmitters in the group. The results of laboratory tests are given which assess the improvement to daytime reception that would result if the times of arrival of the two modulations were equated in these regions. The practicability of implementing such an arrangement is discussed and the preliminary results of a field trial are given.