----------
From: T A RUSSELL[SMTP:n4kg@juno.com]
Sent: Thursday, July 23, 1998 6:12 AM
To: KQ3V@aol.com; TOWERTALK@contesting.com
Subject: Re: [TowerTalk] TA-33 feed
Tom, I think that the BCI and TVI problems that are associated with the
feedline radiation comes from the fact that the radiation is simply closer to
the household electronics. That also accounts for the fact that you get more
RFI pickup on receive, particularly from computer birdies. Thanks to the
inverse square law, those computer birdies really get amplified when your
receive antenna is laying right next to the computer.
The radiation from feedlines not having a balun can EASILY interfere with the
pattern you think you have with your yagi. I was involved with an extensive
test on antenna decoupling at the University of Washington about 20 years ago
with Prof. D.K. Reynolds. It was a real eye opener!!!! Take a 2 meter gain
vertical antenna and with proper decoupling you had and honest 3 dBd gain,
without it you could have a minus 3 dB gain, depending on how much feedline you
put on it. With enough feedline, the antenna SYSTEM becomes a long wire and
the maximum radiation is off the end, not on the horizon. The poorly decoupled
VHF vertical antenna squirts most of its RF straight out into space!!
By the way, this is a dirty little secret, but the FCC guidelines for
determining biological radiation hazards do not take feedline radiation into
account and that can be the BIGGEST contributor of all if someone does not
believe in BALUNS.
73/Mike, N7ML
" I realize a mono should be quieter than a multi-bander,
but I feel the balun made a positive difference on my 33, also. "
And what exactly do you attribute the excess noise to in tribanders?
Where does the excess noise come from?
Antennas have gain and pattern. More gain, more signal from the
desired direction. More pattern rejection, less signal from undesired
directions. This has nothing to do with the number of bands the
antenna will operate on.
Antennas optimized for gain usually exhibit less pattern rejection
than the same antennas optimized for pattern, which usually have
slightly less gain (on the order of 1 dB if carefully optimized).
A balun can reduce feedline radiation (on both tribanders and
monobanders) and thus reduce pickup from undesired directions.
The advertisements indicting feedline radiation as the cause of
TVI and BCI are a joke. Does anyone really believe that feedline
radiation will cause TVI but radiation from the antenna does not?
de Tom N4KG
_____________________________________________________________________
You don't need to buy Internet access to use free Internet e-mail.
Get completely free e-mail from Juno at http://www.juno.com
Or call Juno at (800) 654-JUNO [654-5866]
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search.htm
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|