European region the agreed this technique gives rise to some loss of compatibility (dots and international u.h.f. channels occupy 8MHz; in System I the vision crawl being seen on a monochrome display) and also cross colour carrier is always +1.25MHz from the lower end of the channel; the effects on colour reproduction (flaring of patterned jackets is a FM sound carrier +7.25MHz. Figure 57.4 shows the vision response common example), due to luminance signals appearing in the colour curve of System I as related to the video signal, the r.f. channel, and channels. the standard BREMA receiver i.f. channel. The FM sound is trans- Basically the information in a monochrome signal is distributed mitted with a maximum a.f. signal of 15kHz and with a peak carrier in a series of packets separated by the line frequency, with only little deviation (corresponding to a 400Hz tone at a level of +8dBm at spectrum energy in the gaps between as shown in Figure 57.6. By the modulator input) of +50kHz. The pre-emphasis time constant is choosing a colour subcarrier frequency that is accurately placed 50us. between multiples of the line frequency, and noting that chromin- The use of an asymmetric sideband vision signal results in a ance modulation energy is similarly in the form of packets it is degree of quadrature distortion when the signal is envelope de- possible to interleave the basic energy spectra of the luminance and modulated: this form of distortion (which can usually be detected chrominance signals for 625 line transmission the colour subcarrier only with some difficulty, even on a test card) can be eliminated by frequency is maintained very precisely at 4433618.75Hz :1Hz, the use of synchronous demodulation. with a maximum rate of change of subcarrier frequency not exceed- Although the chrominance signals generated in the colour camera ing 0.1Hz/s. occupy the full range of video frequencies, it is only the luminance The relationship between subcarrier and line frequency is given signal that requires to be transmitted to th