Also, keep in mind that direct radiation into a poorly shielded TV set can
create TVI. In my previous location I used an Orion driving a Drake L-4B,
and the antenna was a ground mounted Butternut vertical. All TV sets were
fed by buried cable lines. Neither my own set or the immediate neighbors had
any TVI, but one neighbor two or three houses away had TVI on the newer of
his two TV sets.
After consulting with someone at his place of employment, the neighbor
informed me that I should install a low-pass filter. I instructed the
neighbor to contact the Cable TV company, and they sent a trouble shooter to
his house. The Cable TV representative was a former ham, and in everyone's
presence I inserted a Bencher low-pass filter at the L-4B output. The filter
made no difference whatsoever. We then went to the neighbor's offending TV
set and removed all wires except the power cord and the antenna cable. We
wrapped the TV's power and antenna wires around ferrite cores, so that
common-mode ingression of my 40-meter SSB signal would be attenuated. This
made no difference either.
The neighbor was told that it appeared that his interference was a case of
direct radiation into an inadequately shielded TV set, and that nothing
could be done to clear up the problem. The fact that my own TV set, as well
as the sets belonging to neighbors who were next door to me, did not have a
TVI problem was a powerful argument that the problem must reside in his own
TV set. He gave the offending TV receiver away to a relative, purchased a
new set and enjoyed excellent TV reception on all his sets.
John, N9JG
----- Original Message -----
Date: Sun, 18 May 2008 01:07:52 -0400
From: "DAVID HELLER" <dtx@verizon.net>
Subject: Re: [TenTec] Low Pass Filter
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Message-ID: <00cf01c8b8a5$214e66c0$4101a8c0@Heller>
Content-Type: text/plain; format=flowed; charset=iso-8859-1;
reply-type=original
Radiation from a feedline or from the antenna proper is radiaton, which is
what a transmitter is supposed to be doing for a living. A good match is
just supposed to increase the amount of transmitter output that actually
gets where it can radiate; that which simply heats something along the way
is just wasted. As for the RFI possibility I refer to the ARRL RFI book,
and especially the article by me therein. The test: If there is one TV set
(assuming it's TVI in question) in your home or the immediate vicinity that
your station does NOT bother your rig is clean and anything you do to it
will produce no improvement. The affected receivers are defective,most
likely needing high pass filtering.
Telephones and other devices that are either not supposed to be receivers or
at worst VHF or UHF devices should know better than to listen to HF.
One rule our Bucks Interference Committee,which I headed for many years,
strictly enforced, was that we of the committee would never touch a
complainant's device - TV or whatever, and we were emphatic in advising the
involved amateurs to keep hands off, and generally keep clear and let the
Committee do the dirty work.
One of the worst sources of true RFI was the ubiqitous C,B, ,often assisted
by the nonlinear amplifiers common to the breed. We stayed clear since our
services were free and FCC had the opportunity to make money off them.
Always amazing how 5 watts could raise so much problems while 100 watts or
even a KW would bother no one.
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