Topband: 160M Helical Vertical

[k3bu at optimum.net]

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 at 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
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