The optical fiber transmission of TV signal performed by a microwave sub-carrier has many advantages: utilizing the mature and relatively cheaper microwave circuit, we can fully utilize the potential of optical fiber bandwidth; utilizing frequency division multiplex technique(FDM), we can transmit analog TV ,digital TV, high definition television(HDTV), digital audio et, so the system is very flexible. Now we need to use the microwave sub-carrier optical fiber transmission system at two situations, one is to transmit multiplex TV signal from earth station to city TV station, the other is to transmit multiplex TV signal from city TV station head-end to the head-end of county or district. At this time, the span of AM-VSB/IM multiplex TV signal transmission system is short, but the base-band video signal from optical receiver must be transformed to AM-VSB signal at the terminal so that the signal can be distributed to the subscribes in the CATV network. With developing the satellite broadcasting TV service, the major program of Chinese CATV network will come from satellite(DFH-3 et.),if we can directly transmit microwave signal which is received at earth station to each CATV station head-end through optical fiber by IM to laser. Not only saving many satellite receivers, AM-VSB mid-frequency modulator, FM mid-frequency modulator, up converter and microwave repeater facility, but also improving the signal quality in the end because of reducing the signal transform link. A practical microwave sub-carrier CATV optical fiber transmission system is shown in figure 1.
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