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The problem heterodyning a 41 MHZ sweep generator down to 21
is that to keep the markers correct you need to have the fixed oscillator
at about 20 MHz, which is too close to 21 even with a balanced modulator.
On the other hand you can heterodyne it UP easily to VHS and run it into the tuner ...
if that is aligned broad enough. You can of course check to see that by trying different channels.
O you can just use the markers at their upside down places and get the shape right,
knowing where they actually are.
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