in subcarrier. luminance level should produce no changes in either amplitude or phase of the color 5 Note that the color subcarrier carries its color information by phase modulation. 16.5 VIDEO TRANSMISSION STANDARDS (CRITERIA FOR BROADCASTERS) 16.5 VIDEO TRANSMISSION STANDARDS (CRITERIA FOR BROADCASTERS) The following outlines video transmission standards from the point of view of broadcasters (i.e., as emitted from TV transmitters). Figure 16.6 illustrates the components of the emitted wave (North American practice). Tables 16.1a and 16.1b give a capsule summary of some national standards as taken from ITU-R BT.470-3 (Ref. 7). 16.5.1 Color Transmission Three color transmission standards exist: NTSC National Television System Committee (North America, Japan, and many Latin American countries) SECAM Sequential color and memory (Europe) PAL Phase alternation line (Europe) The systems are similar in that they separate the luminance and chrominance inform- ation and transmit the chrominance information in the form of two color difference signals, which modulate a color subcarrier transmitted within the video band of the luminance signal. The systems vary in the processing of chrominance information. In the NTSC system, the color difference signals I and Q amplitude-modulate sub- carriers that are displaced in phase by /2, giving a suppressed carrier output. A burst of the subcarrier frequency is transmitted during the horizontal back porch to synchronize the color demodulator. Sound Picture center carrier frequency Chromatic subcarrier frequency 3.579545 MHz 4.2 MHz 4.5 MHz 6 MHz Channel frequency spectrum referred to lower frequency limit of channel (MHz) Figure 16.6 RF amplitude characteristics of TV picture transmission, NTSC/US practice. Field strength at points A do not exceed 20 dB below the picture carrier. Drawing not to scale. TELEVISION TRANSMISSION Table 16.1a Television Standards, NTSC/US Channel width (see 6 MHz Figure 16.6) (Transmission) Video 4.2 MHz Aural +25 kHz Picture carrier location 1.25 MHz ab