[TowerTalk] Modeling a ground plane

[ve4xt at mymts.net]

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 at 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
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