![]() You select the channel on it, it decodes the right signal and then does the same thing a VCR does to transmit the signal to the TV on channel 3 or 4.The cathode ray tube (CRT) is a vacuum tube that contains one or more electron guns and a phosphorescent screen, and is used to display images. Unfortunately, that approach would make theft of cable services very easy, so the signals are encoded in funny ways. Your cable provider could simply modulate the different cable-TV programs onto all of the normal frequencies and transmit that to your house via the cable then, the tuner in your TV would accept the signal and you would not need a cable box. The cable in cable TV contains a large number of channels that are transmitted on the cable. The VCR has a circuit inside that takes the video and sound signals off the tape and turns them into a signal that, to the TV, looks just like the broadcast signal for channel 3 or 4. The video tape contains a composite video signal and a separate sound signal. Almost all VCRs have a switch on the back that allows you to select channel 3 or 4. VCRs are essentially their own little TV stations. In the next section, you'll learn about the color TV signal. All other colors on a TV screen are combinations of red, green and blue. To create a black dot, all three beams are turned off as they scan past the dot. To create a white dot, red, green and blue beams are fired simultaneously - the three colors mix together to create white. When a color TV needs to create a red dot, it fires the red beam at the red phosphor. This mask is perforated with very small holes that are aligned with the phosphor dots (or stripes) on the screen.
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