According to ye olde ARRL Ant. Hdbk (1974), p. 66, Fig 2-87, it IS dependent on
diameter of the elements AND spacing. (See also Jasik, Antenna Engineering
Handbook (1961) for more.)
What handbook are you referring to?
This plot shows S/d2 vs. d2/d1, where S is spacing between the elements, and d1
and d2 are the diameters of the two elements. The latter is interesting, that
the two elements can be of differing diameterm which alters the Z transform
ratio. Usually, they are the same, which gives _only_ a 4:1 feedpoint Z step
up, no matter what vaslue S/d2 is.
However, caution is given that this graph is not useful above 2 meters, oh well.
--John
--- On Thu, 8/27/09, Burt Lang <b...@gorum.ca> wrote:
From: Burt Lang <b...@gorum.ca>
Subject: Re: Fw: Re: [Repeater-Builder] 2 meter folded dipoles for multi bay
design information needed
To: Repeater-Builder@yahoogroups.com
Date: Thursday, August 27, 2009, 3:19 PM
Actually 300 ohms is special. It is the impedance of a
folded dipole
with equal diameter elements, the end result of bending a single piece
of tubing into a U. And the impedance is not affected by the spacing
between the elements (according to the handbook theory).
Burt VE2BMQ
John Sehring wrote:
>
>
> Yes, it does depend on the antenna, to wit, diameter of the elements &
> spacing between the elements. Can be made lower or higher than 300
> ohms. There's nothing "sacred" about 300 ohm Z. It was a match for 300
> ohm TV twinlead in the older daze.
>
> --John
>
> --- On *Thu, 8/27/09, Chuck Kelsey /<wb2...@roadrunner. com>/* wrote:
>
