Quote:
Originally Posted by ppppenguin
With -ve systems you don't need gated/keyed AGC. You can just use the peak level. If the transmitted signal is accurate then peak level and black level have a fixed relationship.
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True. Gating is not necessary, but it improves immunity to impulse noise (like car ignition noise, which used to be a problem). The effects of impulse noise could also be reduced with a noise inverter stage that canceled impulses that went too much blacker than black.
In positive modulation systems, impulse noise would appear as white flashes in the picture instead of black.