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The waving at the top of the screen is called flagging. Its a common problem when time base errors inherent in the tape overcome the receiver's ability to lock onto the sync.
Macrovision is basically a technique of messing with the AGC circuits in a recording deck. It is inserted outside the normal picture region in the upper scan lines of the picture. Basically its a pulsing set of lines that go from 0% (blacker than black) all the way up to 120% (over modulated white). Those percentages are in IRE values.
The solution for all these problems is to get a full frame time base corrector. Its a device used in TV stations to allow helical scan VTR's to be able to be used with live cameras and other stable sources.
The time base corrector will eliminate flagging in the picture. The better one's will also strip the sync and insert a fresh one (without copyguard annoyances).
They're a little pricey for new ones (around $400 for a low end model). But, they're common enough on ebay. If you go for a used one, get a newer one and be sure its full frame, they did make them that only corrected so many lines (memory used to be real expensive), and those won't do anything for Macrovision.
You probably would only need one of them, plugged into your RF modulator for your set.
David
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