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From: fish@ihlpg.UUCP (Bob Fishell)
Newsgroups: net.video
Subject: Re: AC on Cable?
Message-ID: <208@ihlpg.UUCP>
Date: Wed, 27-Feb-85 12:34:13 EST
Article-I.D.: ihlpg.208
Posted: Wed Feb 27 12:34:13 1985
Date-Received: Fri, 1-Mar-85 05:43:37 EST
References: <35@bbnccv.UUCP>
Distribution: net
Organization: AT&T Bell Laboratories
Lines: 34

> 
> 	One of the folks here has cable at home,  and has an
> interesting problem.  Whenever he hooks his stereo up to the 
> cable he gets an AC hum through the speakers [note he doesn't
> need to turn the stereo on to hear the hum].
> 
> 	{The intent was to be able to tune the MTV FM stereo
> portion.}
> 
> 	A test light shows that there is a significant AC potential
> across his cable (perhaps about 110VAC).
> 
> 	Has anyone heard of this before?

*** REPLACE THIS MESS WITH YOUR LINEAGE ***

My cable hookup gave me a similar problem.  I had hooked up the
cable to my VCR, which I then route to my stereo via the audio
out jack.  I noticed a pronounced AC hum which I traced to an AC
potential between the cable's shielding and earth ground.

Connecting a ground wire between the cable and the screw holding
a wall socket cover in place solved the problem nicely.

I don't believe the cable company is deliberately putting AC on
the cable; rather, it's probably picking up some AC voltage
inductively or through a power cross somewhere in the network.
CATV lines are often hung on the same poles as power lines,
so this kind of thing is bound to happen.  In any case, grounding
the outside of the cable will take care of the problem.
/_\_

				Bob Fishell
				ihnp4!ihlpg!fish