Here some info on loading coils and current distribution in loaded resonant
antennas.
http://www.k3bu.us/loadingcoils.htm
In the nutshell: efficiency is roughly proportional to the area under the
current curve along the radiator.
It is better to have loading coil or top loading than distributed helical.
Yuri K3BU.us
----- Original Message -----
From: paulkb8n
Date: Thursday, March 31, 2011 2:36 am
Subject: Topband: 160M Helical Vertical
To: topband@contesting.com
> I've read a lot about the K6MM vertical and may be forced to go
> that route, as the Neighborhood Association has received some
> complaints on my current 160M dipole and I may be forced to
> remove it.
>
> Somehow, I feel that the K6MM design might be improved. I've
> been testing an 80M version using some military-style fiberglass
> mast poles with my helix made out of copper foil tape. This has
> resulted in a much more tidy and easier way to construct the
> helix. I also believe the 1.5 mil foil has less capacitive
> losses between turns than the wire that is used by K6MM. I am
> using a one-quarter inch wide foil tape on my 80M version, and
> with fairly close spacing and a small capacitive hat, I can
> squeeze the antenna size down to only 8'.
>
> I've been testing this antenna indoors in my attic, and it seems
> to work remarkably well. I've gotten decent reports around the
> states, and have worked some modest DX.
>
> I have no idea how the foil tape helix could be modeled. I have
> built several working helical segments using various diameter,
> tape size and pitch, and measurements suggest that using a half-
> wave of foil tape in the helix will yield a quarter-wave of
> electrical length. Every design I've tested seems to show nice
> usable bandwidth against a fairly decent ground (center screen
> and 12 radials). I am wondering how the flat foil tape will
> perform compared to a regular round conductor? Also, what width
> of foil tape would be adequate for 160M use? Has anyone modeled
> or experimented with this? Can the
>
> My 80M version's performance gives me hope that a short 160M
> helical vertical might work effectively as well. Any thoughts
> or suggestions will be appreciated.
>
> Thanks, Paul, K5AF
> _______________________________________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK
>
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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