Double-sideband amplitude-modulation is widely\ud used because of its simplicity in transmission and\ud reception, but in a number of applications the inclusion\ud of a data channel has become an additional requirement.\ud An additional data signal, transmitted with a normal AM\ud broadcast signal, can be used by a specially-equipped\ud receiver to provide for display and control functions.\ud The data signals should not impair the main broadcast\ud signals, and should be imperceptible to listeners with\ud ordinary radio receivers.\ud \ud The principles of a new modulation scheme, which\ud permits an additional data channel to be superimposed on\ud conventional DSB-AM signals without any bandwidth increase\ud or envelope distortion, are described in this thesis. The\ud proposed system uses combined amplitude/frequency modulation\ud to provide for the additional data channel. It is shown that bandlimitation may be preserved by frequency modulating the carrier with frequency-modulating functions\ud related to the complex zeros of the amplitude-modulating\ud signal.\ud \ud The performance of the new modulation technique is\ud assessed by computer simulation. The cross-talk between\ud the two channels due to multipath propagation is considered\ud to be a limiting factor. A novel complex filtering technique to detect complex zeros of realsignals is introduced and discussed. The distribution of the complex zeros of positive bandlimited signals is assessed experimentally, and the possible data rates of the proposed system are discussed
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