----- Original Message ----- From: "Tim Goodrich" <t...@timgoodrich.net> To: <amsat-bb@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 _______________________________________________ Sent via amsat...@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
