Television

14 Pages 3543 Words

Television
By: Ralph Moore

The Fundamentals of Television In this report on television I will discuss television signals, the components the make up a television, and how a television produces the picture and sound for the final output. The sound carrier is at the upper end of the spectrum. Frequency modulation is used to impress the sound on the carrier. The maximum frequency deviation is twenty-five kilohertz, considerably less than the deviation permitted by confessional FM stereo. As a result, a TV sound signal occupies less bandwidth in the spectrum than a standard FM broadcast station. Stereo sound is available in TV, and the multiplexing method used to transmit two channels of sound information is virtually identical to that used in stereo transmission for FM broadcasting. The picture information is transmitted on a separate carrier located 4.5 MHz lower in frequency than the sound carrier. The video signal derived from a camera is used to amplitude modulate the picture carrier. Different methods of modulation are used for both sound and picture information so that there is less interference between the picture and sound signals. The full upper sidebands of the picture information are transmitted, but only a portion of the lower sidebands is suppressed to conserve spectrum space. The color information in a picture is transmitted by way of frequency division multiplexing techniques. Two color signals derived from the camera are used to modulate a subcarrier that, in turn, modulates the picture carrier along with the main voice information. The color subcarriers use double-sideband-suppressed carrier AM. The video signal can contain frequency components up to 4.2 MHz. Therefore, if both sidebands were transmitted simultaneously, the picture signal would occupy 8.4 MHz. The vestigal sideband transmission reduces this excessive bandwidth. Because a TV signal occupies so much b...