Hi,
I agree.
1. Accuracy of modeling. Even with NEC2 or MININEC you get some results and
you get probably lower impedances than the reality but the radiation pattern
is probably more-less correct.
2. There is one software which claims to be a competition to NEC-4 - the
EM-broadcast professional. This is the one I bought (not cheap either - but
no need for complicated licensing etc.) and my experience with real results
field tested - compared to modeling was very good - less then 5% in
impedances. It can handle 10 000 pulses so huge complicated structures can
be modeled - you need some 20-40 segments/wavelength. The software was
written by scientists - so the internal engine is probably good but the
shell around it is scarce and user unfriendly .....
73 !
Jiri
OK1RI
-----Original Message-----
From: Guy Olinger, K2AV [mailto:k2av@contesting.com]
Sent: Tuesday, January 30, 2001 12:40 AM
To: Ji?í ?anda; towertalk
Subject: Re: RE: [TowerTalk] Shadowing of small antennas by larger ones?
>
> 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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