[TowerTalk] How Helically Wound Verticals Really Work (was : Vertical dipoles)

[Steve Hunt]

Rick,

A very interesting topic!

When I try modelling a helical vertical in EZNEC (zero wire loss) and 
then compare it with the same length straight vertical (zero wire loss) 
I do see a slightly increased Rrad for the helical. It's enough that it 
shows up as slightly more efficient if you throw in some ground losses.

Once I include wire losses and add a Q=400 base loading coil for the 
straight vertical, the total losses appear to be within 1dB of each 
other, with the helical having the edge. If I mid-load the straight 
vertical with a similar Q loading coil, its increased Rrad means it 
beats the helical by about 1dB.

I wonder if you have done any similar modelling and have you found the 
helical at a more significant disadvantage?

73,
Steve G3TXQ



Rick Karlquist wrote:
>
> The HWV does not eliminate the loading coil, it just replaces it
> with a very long skinny coil that runs the length of the antenna.
> The radiation resistance of the antenna is not affected by the
> coil.  However, the Q of a long skinny coil with wide spaced turns
> is much less than a conventional coil.  This is simply because it
> takes a lot more wire to make the coil.  In the article, over 250
> feet of wire are used; much more wire than is required for a
> conventional coil.  If you want to prove it to yourself, just
> do a few sample calculations using Wheeler's inductance formula,
> which is in every radio handbook.  You will see that if the length
> of a long skinny coil is doubled, the amount of wire needed goes up
> about 40%.  The loss per foot of wire is basically independent of
> spacing if it is at least a couple of wire diameters.  Therefore, the
> loss goes up 40% with each doubling of length.  Also, winding the coil
> on PVC pipe introduces additional losses due to the PVC.
>
>
>