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[TowerTalk] TA-33 feed

To: <towertalk@contesting.com>
Subject: [TowerTalk] TA-33 feed
From: n7ml@imt.net (Michael Lamb)
Date: Thu, 23 Jul 1998 13:17:14 -0600


----------
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


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