CANCELLER OF INTERFERENCE WAVE CAUSED BY SPORADIC-E IONOSPHERE IN TV RECEPTION.

Abstract

Co-channel interference caused by reflected waves from the sporadic-E ionosphere (Es) has become a serious problem in VHF-TV reception. Reflected waves, which are VHF-FM radio broadcasting waves in neighboring countries, impair the quality of received TV pictures causing 'beat' stripes or color 'beat'. An Es Interference Canceller which compensates the quality of picture impaired by Es interference waves has been developed for TV relay stations. The interference wave is cancelled out by the same interference wave derived from the quadrature component of a TV signal, which undergoes Hilbert-transform after being demodulated by quadrature synchronous detection. Experimental and theoretical analysis have been made and interference wave suppression higher than 40 dB has been achieved. Field tests have also been conducted for single interference waves; the picture is almost perfectly compensated. Even for multiple waves, more than one point improvement is attained on a five-point subjective evaluation scale.