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教育战线上应用的闭环电视(简称教学电视)与在工业战线上用的闭环电视(简称工业电视)不同之处,就在于它在传送图象的同时又要传送伴音,所以教学电视比起工业电视来说要稍微复杂一些。至于在传送图象的同时又要传送伴音的方法主要有二种,一种是视频单线传送,另一种是高频单线传送。这二种方式,各有自己的优点,但是,不论是那一种方式都是利用单线在传送图象的同时又传送伴音,不同之处是高频单线传送是送到电视接收机的高频输入端(代替天线),而视频单线传送是送到电视接收机中的予视放基极。视频单线传输实现的可能性是鉴于下列事实,我们知道电视接收机从天线接收来的无线电波到高频头,经过混频,变成图象中频和伴音中频,再经过中频通道放大后,送到视频检波器进行检波。由于图象中频信号是调幅的,在这里就被检波,得出0—6MC的图象信号。而伴音中频是调频的,不能被检波器检出,但因为它是和图象中频载波一起加到检波器去的,所以二种中频信号在检波器中产生了差频作用,形成伴音的差载频调频信号,也即得到34.25MC—27.75MC=6.5MC的差载频调频信号。这个新的伴音信号一般书上
The difference between the closed-loop television (hereinafter referred to as “teaching TV”) applied on the educational front and the closed-loop television (industrial television) used on the industrial front is that it transmits audio and video while transmitting audio. Therefore, compared with the industrial TV is a bit more complicated. As for the transmission of images at the same time there are two ways to transfer sound, one is the video transmission line, the other is the high-frequency single-line transmission. Each of these two methods has its own advantages. However, no matter which method is used, a single line transmits images while transmitting sound. The difference is that high-frequency single-line transmission is performed on the high frequency of the television receiver Input (instead of an antenna), while video one-wire transmission is sent to the television receiver pre-play base. The possibility of video single-line transmission is realized in view of the fact that we know that the radio wave received by the television receiver from the antenna to the tuner is mixed to become the image intermediate frequency and the audio intermediate frequency and then amplified by the intermediate frequency channel To the video detector to detect. Since the IF signal is amplitude modulated, it is detected here, resulting in a 0-6MC image signal. The audio intermediate frequency is FM, can not be detected by the detector, but because it is with the image IF carrier to the geophone, so the two kinds of IF signal produced in the detector frequency difference, the formation of sound difference Carrier frequency modulation signal, that is, 34.25MC-27.75MC = 6.5MC poor carrier frequency FM signal. This new sound signal is generally on the book