Hi Bill,
At six feet, your radials are still coupling to the Earth and thus being
detuned. Which is why adjusting your radiator has a greater effect. Can't
dismiss also the odds of common-mode current affecting your readings. Do you
use a choke?
I've tried to find the reference but have to leave home now. There is a minimum
height above ground before the radials are truly isolated from ground. For some
reason, the height of 1/4 wl comes to mind.
Which is not to say elevated radials can't work at lower heights: chances are
your radials will be more effective than the same number not elevated. It
merely explains your tuning issue.
I think the work I was trying to find was by N6LF. Cebik may have also done
some work.
73,
Kelly
ve4xt
Sent from my iPad
> On Sep 10, 2014, at 10:36 AM, "Larry Banks" <larryb.w1dyj@verizon.net> wrote:
>
> Hi Bill,
>
> I just built one of these with radials at 10'. Check out my write-up at the
> bottom of my home page: http://www.qsl.net/w1dyj/.
>
> I don't have a real answer to your question, but it probably has to do with
> the effect of "ground." I don't remember seeing much difference when I
> changed the radial vs. vertical length, but I changed them at the same time,
> so I didn't perform the same experiment.
>
> 73 -- Larry -- W1DYJ
>
>
>
> -----Original Message----- From: Bill Turner
> Sent: Wednesday, September 10, 2014 11:11
> To: Towertalk
> Subject: [TowerTalk] Modeling a ground plane
>
> I am modeling a full size ground plane with four elevated radials for
> 40 meters using EZNEC v. 3.0. I have it six feet above ground.
>
> I noticed that changing the length of the radials has much less effect
> on the resonant point than changing the vertical element.
>
> For example, on 40 meters, changing the vertical element by one foot
> moves the resonant frequency by about 200 kHz, but changing all four
> radials by one foot moves the resonant frequency much less, only about
> 20 kHz or so.
>
> I'm curious why this is. I would have thought the effect would be the
> same.
>
> All comments appreciated.
>
> 73, Bill W6WRT
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|