entage 10-12.5% of peak carrier Polarity of transmission Negative; a decrease in initial light intensity causes an increase in radiated power Aural transmitter power Maximum radiated power is 20% of peak visual power Source: Refs. 7, 8. In the PAL system, the phase of the subcarrier is changed from line to line, which requires the transmission of a switching signal as well as a color burst. 16.6 METHODS OF PROGRAM CHANNEL TRANSMISSION Table 16.2a Interconnection at Video Frequencies (Baseband) Impedance 75 So unbalanced or 124 So (resistive) Return loss No less than 30 dB Nominal signal amplitude 1 V peak-to-peak (monochrome) Nominal signal amplitude 1.25 V peak-to-peak, maximum (composite color) Polarity Black-to-white transitions, positive going Table 16.2b Interconnection at Intermediate Frequency (IF) Impedance 75 S unbalanced Input level 0.3 V rms Output level 0.5 V rms IF up to 1 GHz (transmitter frequency) 35 MHz IF above 1 GHz 70 MHz Signal-to-weighted noise ratio at output of final receiver: 53 dB. In the SECAM system, the color subcarrier is frequency modulated alternately by the color difference signals. This is accomplished by an electronic line-to-line switch. The switching information is transmitted as a line-switching signal. 16.5.2 Standardized Transmission Parameters (Point-to-Point TV) These parameters are provided in Tables 16.2a for the basic electrical interface at video frequencies (baseband) and Table 16.2b for the interface at IF for radio systems. 16.6 METHODS OF PROGRAM CHANNEL TRANSMISSION Definition: A program channel carries the accompanying audio. If feeding a stereo system, there will, of course, be two audio channels. It may also imply what are called cue and coordination channels. A cue channel is used by a program director or producer to manage her/his people at the distant end. It is just one more audio channel. A coordination channel is a service channel among TV technicians. Composite transmission normally is used on TV broadcast and community antenna television (CATV or cable