TELEVISION TRANSMITTER

摘要

A television transmitter comprises a video processing circuit (2) an amplitude modulator (4) a vestigial sideband filter (8) an R.F. amplifying stage (9) and a klystron amplifier (10) which feeds an antenna (22). The klystron is provided with a grid electrode (12) to which a video signal is applied to modulate the density of the electron beam. The video signal applied to the grid electrode (12) is derived from the output of the video processing circuit (2) and fed via a low-pass filter (6) and a d.c. isolating circuit (20) to an amplifier (21) which provides a signal of the desired amplitude at the grid electrode (12). The filter (6) is arranged to restrict the bandwidth of the video signal applied to the grid electrode (12) to less than that of the vestigial sideband in order to reduce the possibility of re-inserting the higher frequencies into the vestigial sideband. The d.c. isolating circuit isolates the video signal source from the cathode and grid potentials of the klystron which are typically between 10 K and 30 K volts.