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From: fish@ihlpm.UUCP (Bob Fishell)
Newsgroups: net.video
Subject: Re: HELP! TV/FM Interference
Message-ID: <678@ihlpm.UUCP>
Date: Wed, 22-Jan-86 18:43:53 EST
Article-I.D.: ihlpm.678
Posted: Wed Jan 22 18:43:53 1986
Date-Received: Thu, 23-Jan-86 22:01:59 EST
References: <2425@sdcrdcf.UUCP>
Organization: AT&T Bell Laboratories
Lines: 41

> []
> 
>   I need some help with identifying and, hopefully, correcting a TV and FM radio
> interference problem.  The best description of the problem is noise (static) in
> the audio of the TV and the FM radio.  The video on the television has a tiny
> bit of snow in two distinct bars on the screen; one in the top half and one in
> the bottom half.  The trouble appears periodically in the evening.  I've checked
> with another neighbor and they have the same problem.
> 
This problem has appeared numerous time in this newsgroup, so I thought I'd
post this response.

The problem you describe can usually be attributed to somebody operating
a brushed-contact electric motor nearby.  Power tools are the most common
source.  A brushed-contact motor applies current to the armature windings
by means of direct electical contact with a sleeve on the rotor.  There are
gaps in the sleeve, and when the brush crosses the gap, you get sparks.
Anybody who has ever used a power drill can see them.  The greater the load
on the motor, the bigger the sparks.

One of my old professors had this comment about the bandwidth of a spark:
"you can hear it, and you can see it."  In other words, it's a pretty good
source of RF noise.  The only solution is to find out who's running the motor
and complain.  It's probably a router or a saw, something like that, or it
could be a vacuum cleaner.

Your washing machine, furnace, and refrigerator don't bother the TV because
they use brushless, induction motors, which don't spark.  Tools are another
story.  If you want to see the phenomenon for yourself, just run your drill
in the same room as the TV set; you will see the same kind of disturbance
you describe.  

It's kind of funny that the FCC bitches about EMI from computers, but does 
nothing about power tools.  Maybe it's all that military stuff the gummint 
buys from Rockwell.
-- 
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				Bob Fishell
				ihnp4!ihlpm!fish