Quote:
Originally Posted by radiograham
The 625 line signal consisted of vision and sound carriers,vision being amplitude modulated and the sound was fm.When using a vcr rf output does the vcr modulator output consist of the same ie vision am modulated and sound fm?also what is the output from a uhf modulator when fed from say a dvd player,is this the same? Regards Graham.
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The analogue transmitters (the main ones not necessarily the relay stations) combined the output of two separate UHF transmitters, the FM sound transmitter being 5.996MHz higher than the AM vision.
The little modulators in VHS machines simplified this, the vision modulated the UHF carrier and it is mixed with a 6MHz oscillator with the FM sound applied. This mixing causes the sound carrier to appear in the expected place, and also an unwanted sound carrier to appear below the vision as well, but the vision itself will be double-side-band anyway, in a transmitter the vision was vestigial side-band.
The receiver doesn't care too much about these fudges and produces a reasonable picture and sound.
I hope that goes some way to answer your question.