In a message dated 8/20/01 10:57:01 PM Pacific Daylight Time,
thompson@mindspring.com writes:<<
The main problem with bringing ladder line or any open wire line into the
shack lies with what I call the "hot shack" syndrome.
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.
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 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.
73 Dave K4JRB
>>
If and when the problem explained above occurs, this is a good idea. I have
not had it so far with either a Hi-Z or a Lo-Z area at the end of the
feedline. At my new QTH I will have many feedlines coming in the shack and
I'll see which one is the least troublesome if it occurs..
You mention having a remote Balun in the form of a big L.. That will match
any Z at the end of the open wire line. You didn't say if it was remotely
tuned from the shack which would be ideal. Did you have some way to prevent
RF Spill Over around the unblanced tuner? Measures had a good article in QST
on how to make a form of a balanced L that would be ideal. If remotely
tune--ever better.
There is a way to make a L tuner remotely tuned with a 110VAC selsyn motor
driving just one shaft. I call it the "One Knob Antenna Tuner." It tunes up
real fast.
There is another L configuration I use that is actually balanced with out
toroids or rolls of coax for whatever it might do. It also can be tuned on
just one shaft with a remote selsyn. A counter dial would be ideal for
calibration purposes. k7gco
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