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From: karn@petrus.UUCP (Phil R. Karn)
Newsgroups: net.video,net.audio
Subject: Re: Digital audio adapters on VCRs
Message-ID: <700@petrus.UUCP>
Date: Sun, 24-Nov-85 05:07:01 EST
Article-I.D.: petrus.700
Posted: Sun Nov 24 05:07:01 1985
Date-Received: Fri, 29-Nov-85 08:03:49 EST
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Xref: watmath net.video:1696 net.audio:6652

Blush. I guess I owe RCA at least a partial apology.

The major cause of the problem turned out to be a ground loop formed by the
ground on the Tek scope I was monitoring the video signal with and the
ground of my cable TV feed. Disconnecting either the scope or the CATV feed
from the wall cleared things up dramatically. It turns out that there is
about 2v p-p of harmonic-rich AC potential between my CATV feed and the
local power outlet.

What's strange is that the effect of the hum was noticeable only on
playback, even though it was there during E-E (electronic-to-electronic)
loopback during stop mode. I guess only when the hum was combined with the
playback degradation of the VCR was it enough to cause the PCM-F1's error
correction circuits to have problems. Or perhaps the video clamper in the
PCM-F1 wasn't as effective on a noisy playback signal.

The overshoot on playback is still there, of course, and I'd still like to
know if there is an easy way to eliminate it by flattening out the VCR's
phase and frequency response.  Clicks and pops do still occasionally occur,
and I'm sure that cleaning up the "eye" pattern would make these less
frequent.

Phil