Samples of the amplitude of a quadrature amplitude modulated (QAM) subcarrier signal are taken at times corresponding to each axis crossing of each of the two quadrature related signal components. The polarity of alternate ones of the samples is inverted and the signal is reconstructed from the inverted...http://www.google.de/patents/US4286283?utm_source=gb-gplus-sharePatent US4286283 - Transcoder
