Scanning systems which have double rate scanning frequency or 1125/60/2 : 1 HDTV of Hi-Vision, are discussed. Those are 1125/60/1 : 1 (progressive scanning), 1125/120/2 : 1,1125/120/4 : 2 and 2250/60/2 : 1. These systems have different merit on picture quality improvement. Scanning conversion between the systems and Hi-Vision is also discussed, that is important for transmission (and recording) of pictures by the systems and compatibility with Hi-Vision. Experimental devices for the double rate scanning systems have been developed. These devices, especially a image enhancer for the double rate scanning camera and a processor for recording of the double rate scanning pictures are described.

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Scan conversion techniques for letter-box EDTV system are discussed in this paper. Conversion from 480p format (480 lines, progressive scanning) to 360i format (360 lines, interlaced scanning) is divided into two processes, 480p→360p and 360p→360i. The conbination of a new 5×5-matrix conversion (480p→360p) with 2-lines averaging (360p→360i) is an effective method for better picture quality on NTSC receivers.

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A digital audio signal transmission system in which high-quality digital audio signals are multiplexed in the video carrier by using an quadrature modulation method is proposed. Since ghost is generally in terrestrial broadcasting, interferences of video and digital audio signals are occured. We have proposed quadrature ghost cancel reference signal detect those interferences.

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Using quadrature modulation of the video carrier, digital sound as well as high frequency component of side panels can be transmitted while keeping the compatibility with NTSC. In this system, if a ghost occurred, phase error of detection axis would occur too. Also crosstalk from main signal quadrature distortion would come up, then multiplex signal would be degraded. In order to receive the multiplex signal without distortion, we used two dimensional waveform equalizer which can compensate the detection axis and eliminate ghosts of the multiplex signal, crosstalk from main to multiplex signal and quadrature distortion. The experimental result show the residual crosstalk is reduced 5dB more than the conventional two dimensional waveform equalizer without phase compensation, when -12dB, 90 degree ghost exists. Both of residual ghosts and crosstalk can be reduced to a level to 36-40dB (D/U).

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