>
>
>The main problem with bringing ladder line or any open wire line into the
>shack lies with what I call the "hot shack" syndrome.
// This suggests that you have been using a so-called "balanced" tuner
that consists of an unbalanced - usually T - matching network followed by
a balun. I used to run one of these, and I got singed fingers if I
touched the (grounded) chassis of the antenna tuner when transmitting.
This circuit is also known as the "Ultimate Transmatch". The ultimate
apparently comes from the ultimate finger-warming feature on cold
mornings. RFI-proofing the electret microphone took a bit of doing.
>With more than one 160 meter antenna the shack was full of hot RF and
>plenty of RF feedback. This also gets into the telephones
>radios, and even TVs that are not on cable. Even using a tuner with a
>balun can cause a problem.
>
// If there is a balun on the high SWR side -- i.e., the output side of
the tuner, the balun's location is a problem. Baluns are current
friendly, not voltage friendly, and high VSWRs mean the latter.
>This is another form of fundamental overload. The cure is to remove the
>ladder line from the shack (by as many feet as possible). I found that
>using a remote balun (does not matter what values..) just outside the shack
>window still causes problems ...
// but of course. To keep RF out of the shack, the balun needs to go
between the radio and the matching network. Such a tuner appears in the
February, 1990 *QST*. Also, the tuner ground and the station ground need
to be separate from each other. At 28MHz, 10-inch diameter copper pipe
is a quarter-wave RF-choke if it is 8-feet long.
> ... although far less severe than bring ladder line
>directly into the shack. A better approach is to move the remote balun to
>40 feet or more from the shack. I did this with a big L I had up several
>years ago and the amount of RF in the shack was minimal.
>
cheers, Dave
>
>
>
>List Sponsored by AN Wireless: AN Wireless handles Rohn tower systems,
>Trylon Titan towers, coax, hardline and more. Also check out our self
>supporting towers up to 96 feet for under $1500!! http://www.anwireless.com
>
>-----
>FAQ on WWW: http://www.contesting.com/FAQ/towertalk
>Submissions: towertalk@contesting.com
>Administrative requests: towertalk-REQUEST@contesting.com
>Problems: owner-towertalk@contesting.com
>
>
- R. L. Measures, 805.386.3734,AG6K, www.vcnet.com/measures.
end
List Sponsored by AN Wireless: AN Wireless handles Rohn tower systems,
Trylon Titan towers, coax, hardline and more. Also check out our self
supporting towers up to 96 feet for under $1500!! http://www.anwireless.com
-----
FAQ on WWW: http://www.contesting.com/FAQ/towertalk
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
|