Topband: Effect of current max not at base of vertical.

[Charles Moizeau]

> Date: Sat, 17 Sep 2011 17:38:09 -0500
> From: mikewate at gmail.com
> To: topband at contesting.com
> Subject: Re: Topband: Effect of current max not at base of vertical.
> 
> Guy,
> 
> I'm not saying that I understand this 100%, but I certainly do find it
> fascinating. I have a question, though.
> 
> For quite some time, my understanding has been that by making a bottom-fed
> vertical (or inverted-L) longer than 1/4λ --and thereby raising the max
> current point-- that we simply move the point of maximum current farther out
> on the radials. This makes sense to me, if we consider the thought that the
> ground is an image of the antenna, the "missing" portion (for lack of a
> better expression).
> 
> Other well-respected hams used to say that this condition significantly
> added to the requirements for the radial system under such a longer vertical
> in such a way that we now need even longer radials. Later, though, one of
> these hams seems to have reversed his beliefs 180°. I don't pretend to know
> the answer. (And at this point, I'm not sure anyone does. :-)
> 
> If I use a 5/16λ or 3/8λ inverted-L, how does this change the requirements
> of:
> 
> 1. ~60 radials stapled to the surface of the earth ?
> 2. An elevated counterpoise (which would of course require far fewer
> radials) ?
> 
> Thanks,
> Mike
> www.w0btu.com  I have the same issue and opinion that Mike describes, although my thoughts on how to deal with it are different.  The point of difference is that I just don't want to put my hand in a bag of snakes fussing with the erection and tuning of elevated radials that in my case must weave around trees within a wooded area. My inverted L is 85' up and 85' out in the belief that its point of maximum current is located half way up the vertical leg.  There are 55 in-ground radials, most of them 120-160 feet long (a dozen are only 75' long).  My thought is that instead of adding more radials originating at the base feedpoint and extending each of them out 120-160 feet, there would be economies of copper and labor to "crow foot" those additional radials.   By "crow foot", I mean digging up an existing radial at, say, 60 feet out from the base feedpoint and splicing in a new radial that would fit within the interstice of two existing radials and would itself be only 60-100 feet long.  And, by extension, repeating this crow footing at, say, another 30 feet away, splicing and siting each new radial between pairs of then-existing radials.  As such, the newest radials would be only 30-70 feet long     By this means I would avoid what I judge to be an unnecessary intensification of radial density close to the feedpoint, and instead deploy the copper further away and at areas where the existing radials are extremely far apart from one another. Charles, W2SH       
 
>