Hi Jason; some ideas for you to kick around with local hams who may
have had the same problem.
It depends on how the TV signal reaches the TV sets - are they on a
common antenna system, or are they on separate antennas ?? Is the TV
signal strength good ?? For best results it helps to have a strong TV
signal, because you can afford to "lose" some of it in filters.
If the sets are on cable, then I might guess that there is a cable
shield break somewhere which is allowing pickup on the shield which
then takes the picked-up signal directly into the TV set, where it
swamps the front end. Break thru on cable is not usual (over here
anyway).
If the sets use a coax fed external antenna, then the betting is that
the coax braid is acting as an antenna at ham frequencies. If so, you
probably need some form of high pass filter which also breaks the
braid adjacent the TV set antenna socket. I use a pair of one turn 2
inch diameter Faraday loops taped back to back just ahead of the
antenna socket on our video. There is no DC connection at this point,
only magnetic coupling at VHF and upwards (our TV is at 800 mHz
plus !) More pokey filters use a high pass network that not only
breaks the braid connection, but also looks like a dead short to HF
band RF.
The chances of there being sufficient harmonic energy from your rig
to cause a problem are slight; a low pass filter will help only if the
rig's harmonic suppression is awful - and if you have no ATU. Most
ATU's especially TenTec, act as a low pass filter anyway.
My advice is to concentrate on the TV sets and how the signal gets
into them ... Nothing you do at the rig end will help much, if at all.
Unless of course you have a TV antenna right next to a ham antenna
in which case you may need to re-locate one antenna to minimise
coupling. Vertical antennas seem to be the worst ones in such a
case.
Finally, I run 400w from a Hercules II into a 40m inverted V at 55
feet sloping to the same height as our UHF TV antenna. They are 25
ft apart at the closest point, but there is not the slightest sign of
break thru on our TV set or video. Some TV sets further away have
problems, mainly due to bad design, poor installation (especially
poor TV antennas). I keep the TV running when I'm on the air, in case
a neighbour arrives toting a carbine. It always helps to have a clean
picture at home, especially in the shack. I do have a 6kw ICE low pass
filter in the line to the ATU, but it makes no difference. It looks
impressive though (and its a darned good filter).
A recent official inspection including a harmonic sweep made directly
on the rig output found nothing worth mentioning.
Good luck in adapting my comments to US conditions ..!
On 09-Feb-99 jreber@es.com wrote:
>
> Gentlemen:
> I recently purchased an Omni D, and have been using it for about a
> week now.
> It is a wonderful rig, and I can see why so many hams love Ten Tec
> gear.
> However, I have noticed a slight bit of TVI noise in the television
> sets in
> my home- appearing as a single or mulitiple lines through the
> picture, and
> only occuring on channel 2-5. It is worst on channel 2, which
> doesn't come
> in that well anyway. I never had problems with TVI with my other
> rig, a
> hallicrafters FPM-300 with tube type final amp. I'm wondering if
> the broad
> band solid state amp in the Omni D is causing harmonics, and if any
> one has
> used a low pass filter with their Omni D successfully? I have never
> tried a
> low pass filter but would give one a try if I thought it would
> help. Also,
> if anyone has other suggestions, please let me know.
> Thanks,
> Jason KA7UAM
>
> --
> FAQ on WWW: http://www.contesting.com/tentecfaq.htm
> Submissions: tentec@contesting.com
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> Problems: owner-tentec@contesting.com
> Search: http://www.contesting.com/km9p/search.htm
----------------------------------
E-Mail: patents@dx0man.prestel.co.uk
To: <tentec@contesting.com>
Date: 09-Feb-99
Time: 19:35:06
John Crux
Consultant in product forgery - Asia and
Africa
----------------------------------
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