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From: rpw3@redwood.UUCP (Rob Warnock)
Newsgroups: net.ham-radio
Subject: Re: FM Intercom/TV Interference
Message-ID: <192@redwood.UUCP>
Date: Fri, 22-Mar-85 06:14:46 EST
Article-I.D.: redwood.192
Posted: Fri Mar 22 06:14:46 1985
Date-Received: Thu, 28-Mar-85 01:42:27 EST
References: <9359@brl-tgr.ARPA>
Organization: [Consultant], Foster City, CA
Lines: 38

+---------------
| ...bought a wireless FM intercom for my house (two-station).  It works fine
| until I turn the TV on, then buzzes like mad.  I tried a Radio Shack AC
| line filter, but that didn't have any effect at all.  It also makes the
| noise no matter how far from the TV either station is.
| So, what is causing the buzz? ...  And how do I quiet the little
| bugger down? |   John (DINGMAN@RADC-20.ARPA)
+---------------

You don't say what frequency the intercom works on, or anything about
your T.V., so this is pure speculation:

Try cleaning the inside of your television very well, particularly the
high-voltage lead to the picture tube, and all around where it plugs
into the picture tube (especially the glass between the connector and
the conductive outer coating). There can be arcing or corona discharge
through the accumulated dust (which is naturally attracted to the high-
voltage D.C. areas) causing your RFI problem. The corona can also occur
in other parts of the high-voltage system.

** BE VERY CAREFUL! **  If you do not understand the safety precautions
yourself, don't attempt to do it. Get a hardware wizard or service person.
(There is a trick to discharging the tube, which can store a nasty shock.
While said technique is quite easy, I couldn't safely attempt a detailed
decription here, beyond saying it basically involves slipping a grounded
probe up under the insulated "nipple" of the high-voltage wire.)

Another possibility is that the one of the horizontal or vertical output
stages has a parasitic oscillation in the F.M. band (somewhat harder to
diagnose and cure). Borrow a wide-band receiver to check this one out.


Rob Warnock
Systems Architecture Consultant

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