Re: NEC-LIST: HEMAC matching

I believe it was indeed George Hagn. My friend and colleague Brian Austin
also had a student project along the same lines as I recall. This would
have been at the University of the Witwatersrand, Johannesburg, South Africa
many years ago.

Best regards,
Duncan Baker.

-----Original Message-----
From: nec-list-bounces+duncan.baker=ieee.org_at_robomod.net
[mailto:nec-list-bounces+duncan.baker=ieee.org_at_robomod.net] On Behalf Of
Jacob Schanker
Sent: 17 April 2007 09:05 PM
To: nec-list_at_robomod.net
Subject: Re: NEC-LIST: HEMAC matching

Folks:

I believe Chuck is referring to George Hagn, who did many many interesting
antenna and propagation studies. George passed away on August 7, 2004.

Regards,

Jacob Z. Schanker, P.E.
65 Crandon Way
Rochester, NY 14618
585 442 3909
j.schanker_at_ieee.org

"Chuck Counselman" <ccc_at_space.mit.edu> writes:
> At 11:26 AM -0400 4/17/07, D. B. Miron wrote:
>>Do you mean helix rather than toroid? I imagine a helical coil wound
>>around a tree trunk, spiraling up, would give better coupling than a
>>toroid. Have you, or someone else, done this?
>
>
> He means toroidal. This has been done, and it has worked. The last name
> of the person who told us about it on this list escapes me at the moment.
> IIRC, his first name was George; he developed the technique during the
> Vietnam war while working for the U S Army, possibly as a contractor (as a

> staff member of Stanford Telecommunications Inc.?); and he used it
> successfully in Vietnam.
>
> After reading his report on this list, I used NEC-4 to simulate an
> air-core toroidal winding around the trunk of a tree rooted in soil. IIRC,

> the technique worked plausibly. I do not recall the electrical
> conductivity that I assumed for the tree trunk, or for the ground for that

> matter. Nor do I recall NEC-4's computed efficiency of the tree antenna.
>
> Think of the tree trunk as a single turn through, along the axis of, the
> toroidal winding and you will see why a toroidal winding is just what's
> required to excite the tree as a vertical antenna.
>
> Another method of exciting the tree is to drive two metal spikes into the
> trunk, one near the ground and the other at a height above ground chosen
> so the impedance seen looking into the terminal-pair formed by the spikes
> is, e.g., 50 ohms. Then you connect a coaxial feedline directly to the
> spikes. (I would put ferrite common-mode chokes on this coax.)
>
>
> -Chuck W1HIS
>
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>
>

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