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.
>
>
>
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