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Saturday, 3 May 2014

TV Standard and Frequency Requirements

TV Standard and Frequency Requirements:

(a).American Standards: Figure (a). The band of frequencies assigned to a station for transmission of the signal is called a channel. Each TV station has a 6 MHz channel within specific bands for commercial broadcasting.

(i) Video Modulation: The 6 MHz band width is needed for picture carrier signal. The carrier is amplitude modulated by the video signal.

(ii) Chrominance Modulation: For color broadcasting 3.58 MHz chrominance signal has the color information. The color signal (C signal) is combined with luminance signal (Y signal) to form one video signal that modulates picture carrier wave for the transmission.

(iii) Sound Signal: In 6 MHz channel, sound carrier signal for the picture is also included. The sound carrier is a frequency modulated signal by audio frequencies between 50 Hz to 15 kHz.

(iv) Carrier frequencies: The figure (a) shows how different carrier signals fit into the standard 6 MHz channel. The picture carrier frequency is always 1.25 MHz above lower end of the channel. At opposite end, the sound carrier frequency is 0.25 MHz below the high end.

figure (a) Broadcasting Channel (American Standards)
(b).Indian Standards: The total channel width used in India is 7 MHz. The spacing between picture and sound is 5.5 MHz and between picture and color signal is 4.43 MHz. The figure (b) shows the complete spectrum. 
figure (b) Broadcasting Channel (Indian Standards)

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