RE: NEC-LIST: Helix antenna on ground plane

Thanks for the inputs.

I found the mistake, it was the diameter being too long and the
frequency range was set too wide I the resonant was not easily
noticed. I was actually modeling a normal mode helix on the ground
plane around 150 MHz. The result is attached below. I approximated
each turn with 6 wires.

regards,
Sooliam 9W2SL

C:\MININEC\FHGH3 06-29-1998 18:18:44

IMPEDANCE
frequency resistance reactance impedance phase
(MHz) (ohms) (ohms) (ohms) (deg)
source = 1
148. 3.107815 -18.87961 19.13369 279.35
149. 3.192353 -10.03812 10.53352 287.64
150. 3.279385 -1.149066 3.474869 340.69
151. 3.3681 7.77037 8.468927 66.57
152. 3.46112 17.02455 17.37281 78.51

> ----------
> From: CrazyLeddy_at_aol.com[SMTP:CrazyLeddy_at_aol.com]
> Sent: Friday, June 26, 1998 8:24 PM
> To: nec-list_at_ee.ubc.ca
> Subject: Re: NEC-LIST: Helix antenna on ground plane
>
> There are two problems that I think might be causing the bad readings.
>
> First of all, you simply could not be using an accurate enough model.
> Not likely, though, because a hexagon is a pretty good approximation
> of a circle.
>
> A more likely cause would be that the helix is attached to the ground
> plane. Don't forget, MiniNEC assumes that two touching surfaces are
> connected. If you had the height above ground equal to zero, then
> MiniNEC would have had your antenna connected to the ground.
> Solution: Make your antenna a very small distance above-ground.
>
> Finally, your approximation may have changed the resonant frequency of
> the helix.
>
> I hope these few suggestions have helped.
>
> <<Lawrence Weinstein>>
>
Received on Tue Jun 30 1998 - 09:48:57 EDT