[amsat-bb] Re: quadrafilar helix for 70cm- ambiguous design specs

[i8cvs]

----- Original Message -----
From: "Tim Goodrich" <tim at timgoodrich.net>
To: <amsat-bb at amsat.org>
Sent: Monday, September 28, 2009 9:45 PM
Subject: [amsat-bb] quadrafilar helix for 70cm- ambiguous design specs

> Hi All,
>
> The house I just bought precludes me from even using my arrow inside as
> there must be something un-RF friendly in the walls. Therefore, I was
> looking for a roof antenna and the October QST article on the QFH inspired
> me to build one. However, after doing some research, I have come up with
two
> sets of design specs and I'm unsure which one is correct.
>
>
>
>  I converted everything from you're the 146Mhz QST model to 436Mhz.
However,
> when I plug that info into http://www.jcoppens.com/ant/qfh/calc.en.php
>
> The values it puts out are different in the "compensated length" field.
The
> only difference is this model calculates for a full turn as opposed to a
> half turn, but the lengths shouldn't be as different as it says. Under the
> QST model, I get a wavelength of 688mm, but under the website's model, it
> gives me a "compensated wavelength" of 729mm.
>
>
>
> The values I used to calculate are:
>
> 436
>
> 1
>
> 1
>
> 15
>
> 2
>
> .23
>
>
>
> Can anyone tell me which specs to use and/or explain this compensated
> wavelength issue?
>
>
>
> Thank you,
>
> Tim
>
> KI6VBY
>
Hi Tim, KI6VBY

Read please the book "REFLECTION" Transmission Lines and Antennas by
M. Walter Maxwell, W2DU Chapter 22 The Quadrifilar Helix Antenna pages
22-1 to 22-23 and also
"Experimental Investigation of Quadrifilar Helix Antennas for 2400 MHz" The
AMSAT Journal May/June 2004
In a separate email I have sent to you both articles as an attachement.

73" de

i8CVS Domenico