>
> From: Ji?í ?anda <jirka@jimaz.cz>
To: <towertalk@contesting.com>
> Date: 2001/01/29 Mon PM 10:43:06 EST
> To: "towertalk" <towertalk@contesting.com>
> Subject: RE: [TowerTalk] Shadowing of small antennas by larger ones?
>
> The effect of large antenna close to a smaller one is always HUGE.
No, not ALWAYS. Definitely CAN be huge. In the case of the F12 x40N series of
antennas, the linear loading produces an antenna that is not resonant at 15
meters, as opposed to the usual problem with a 40 meter antenna's secondary
resonances detuning 15 on the tribander. They have designed and tested the x40N
antennas to have minimal effect mounted within ten feet of their tribanders
(some say they have used eight).
Modeling using anything other than the hugely expensive NEC4 does not properly
model the linear loading of the x40N elements. So unless you have spent the
money for that software, you would not have a way to gauge how an N element
modifies or is modified by a proximate tribander.
Changing the elements, placement on tribanders is quite a trick affair,
especially those using the F12 kinds of techniques. The modeling REQUIRES field
testing for validation and subsequent fudge factors to make modeling track
reality. It's not like doing dipoles and loops.
73, Guy.
> Try to
> model it and you will see. The effect can be eliminated by changing the
> sizes of the given antennas, the results are often unpredictable.
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