> -----Original Message-----
> From: Tom Rauch [mailto:w8ji@contesting.com]
> Sent: Tuesday, June 28, 2005 10:17 AM
> To: k2xx@swva.net; Buck - N4PGW
> Cc: towertalk@contesting.com
> Subject: Re: [TowerTalk] 135 foot dipole, 300 ohm twinlead
>
>
> > Buck, something isn't right. A properly constructed and
> tuned balanced
> > feed line antenna should be less likely to generate TVI
> than a coax fed
> > antenna because there should be little or no radiation
> from the feed
> > line.
>
> There isn't much difference at all if any. The radiation
> comes from common mode currents, and either could have
> problems. Actually twinlead radiates slightly more if
> everything is perfect, but the amount of radiation from
> either is negligable unless something is hosed up.
>
> > If you're tuner uses a ferrite balun, it could be
> saturating and
> > generating all sorts of spurious radiation.
>
> Ferrites are the materials of choice in baluns. It could be
> a VOLTAGE balun, rather than a current balun. It could be a
> poor balun design or bad balun constuction. What kind of
> tuner and balun is it?
>
>
The tuner is the TenTec 247. The problem is everywhere on the TV. The balun
is a toroid wrapped in wire inside the tuner.
> > >I had a 129 foot dipole fed with CATV coax. It did ok,
> but where the
> > >aluminum met the copper, it oxidized and I have been
> suffering with AM
> > >broadcast band bleedover on all frequencies below 14 MHz.
> I recently
> > >replaced it with a 135 foot dipole fed by 300 ohm TV
> twinlead to my tuner on
> > >which my IC-706 sits. The problem I have now is TVI.
> When I get the
> > >antenna tuned and run more than 30 watts, the TV pictures
> turn red, green,
> > >or blue. We are on Cable TV and I cannot recall the last
> time I had TVI
> > >other than when I operated 6 meters and the rig is
> sitting less than two
> > >feet from my TV. (the TVI now is all over the house.) I
> don't know if it
> > >is getting into neighbors homes at this time.
>
> If the problem is on all channels, it sounds like common
> mode RF. If it is common mode RF, both the TV system and
> perhaps your antenna may be at fault. Certainly the TV
> shares some or most of the blame, unless you have a heap of
> problems.
>
It is also causing noise on 2 meters occasionally.
> If the problem is channel specific, like say only on low VHF
> channels, you most likely have harmonic issues.
Nope! It is on all channels.
>
> I'd sort out what the problem is Buck by giving enough
> information, otherwise anything anyone says is nothing but a
> wild guess. My wild guess at the moment is you have an
> unbalanced feedline condition resulting in common mode
> currents on the chassis of your equipment.
>
> What tuner?
TenTec 247
> What balun?
Internal balun made of a toroid wrapped in wire.
> How is the twinlead routed? Is it kept away from other
> things?
Outside it hangs from the antenna, drops to about a foot above the ground
and comes into my window along with several pieces of coax. It goes under
my desk about 6-8 feet and wraps back to the top to the tuner.
I am considering the dual coax connection described in another reply to keep
the lead from having problems with surrounding metals.
> What channels are affected?
I haven't checked but it seems to affect 5, 46 and many others. (cable tv)
>
> 73 Tom
>
>
>
Thank you
Buck
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