[Elecraft] Helix-wound EDP

[Geoffrey Mackenzie-Kennedy]

Morning Thom,

This type of antenna element has been around for a long time, since the late 
1930s perhaps before, and bears the family name 'Normal Mode Helix'.

Two rules of thumb. For an element that is electrically a quarter wavelength 
long, the overall physical length of the helix should not be less than 0.05 
wavelength e.g. roughly 7ft at 40m. Secondly, the diameter of the 'coil 
form' must be small - 4 inches would probably be OK below 21MHz, but I would 
have to check that. When the diameter is very large, the element becomes an 
'Axial Mode Helix' with the main radiation lobe off the end of the helix, an 
antenna often used at VHF and up.

As an approximation, the length of wire required for a quarter wavelength 
element is close to a half wavelength when wound with equal spacing between 
turns.

If you would like I can send you some much more detailed info ( and a little 
maths!).  Which bands do you want to use?

73,
Geoff
GM4ESD


Thom R LaCosta <lacosta at bcpl.net> wrote:

> Has anyone ever tried/know about winding a w3edp style antenna on a pvc 
> pipe?
>
> I have hardly any space...and every time I manage to get an antenna attach 
> to "Ye Olde Phone Pole","Ye Olde Lineman" arrives and removes it with 
> particular prejudice and dispatch.
>
> I recently obtained a 5 foot piece of 4 inch diameter underground pipe 
> that
> could be used as a form.