[old_tv_nut]

Just FYI, when digital came in, the existing color transmitters could be used, but the exciters had to compensate for the remaining non-linearities. The goal was for the non-linearities to produce an error rate equivalent to a noise floor of -27 dB. This amount would not cut into coverage area with receivers having the usual 15 dB threshold. (Distortion equivalent to -15 dB would put all receivers at threshold, no matter how close to the transmitter. Distortion between -15 and -27 would add significantly to thermal noise and bring the threshold contour closer to the transmitter.)

The digital exciters use feedback of an output signal sample to automatically linearize everything. This could also have some effect on out-of-band splatter, but typical setups use a multi-pole sideband filter to really quash the lower sideband and then depend on the exciter non-linear and linear distortion corrections to make the inband error floor below -27 dB. Typical gear gets well into the minus 30s last time I paid attention. This means that the distortion margin is entirely available to the receiver to accomodate ghost conditions, antenna response, receiver noise figure and receiver IF frequency response.