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

Tim Goodrich tim at timgoodrich.net
Mon Sep 28 12:45:38 PDT 2009

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:








Can anyone tell me which specs to use and/or explain this compensated
wavelength issue?


Thank you,



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