In Japan, the interference against TV channels caused by Duct or Sporadic-E propagation of neighbouring countries'FM or TV broadcast waves is one of the most serious problems. The canceller of this interference was developed and started to use practically in May 1986 at two NHK TV relay stations in Tottori prefecture. The canceller could reduce the beat interference about 40 dB. According to the evaluation of pictures recorded by VTR before and after cancellation, compensation was almost achieved.
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