Hi William, PE1RAH
In a separate email I have sent to you copy of my article "Experimental Investigation of Quadrifilar Helix Antennas for 2400 MHz that was published into the AMSAT Journal May/June 2004 particularly covering the infinite balun theory and applications if you need a End-Fire or Back-Fire radiation from the Antenna.
Also I added an article written by Walter Maxell W2DU one the well know guru about the Helix Antennas.
Finally I have added an artiche that I have written for Radio Rivista about a QFA for 70 cm but sorry it is in italian but you can read the drawings.
Best 73" de
i8CVS Domenico
----- Original Message ----- From: "William Leijenaar" pe1rah@yahoo.com To: amsat-bb@amsat.org Sent: Saturday, January 21, 2012 11:19 PM Subject: [amsat-bb] Quadrifilar Helix antenna question
Hi AMSAT's,
Because I can not set up my rotor/elevation system at the new QTH, I try to get some omni antenna's to be active on the OSCAR's. I made a 2m version and 70cm version from some calculation website (www.jcoppens.com) on the internet. Unfortunately both were too low resonant in frequency. Cutting the lengths shorter, (to get a higher resonance frequency) didn't work well, as I got too short elements at a certain time and the mechanical construction didn't allow more shorter elements.
So I started all over again, this time taking the well known Rothamel antenna book as example. There is an GPS example which I re-calculated to a 70cm version and combined it with an infinite balun that is also described one page further. For the elements (one element as infinite balun) I used Aircell-7 coaxial cable. When I measured this antenna it surprisingly had also a too low resonance frequency, some 60MHz lower then the expected 435MHz... Another thing I noticed is that the return loss is around 10dB best case for this kind of helix antenna (that's at 375MHz resonance). It gets better when I touch the elements, but that should not be the way it should work...
Does anyone has experience with quadrifilar helix antenna's on 2m and 70cm for TX ?
When using the infinite balun principle, should it be a number of 1/4 wavelength ? or should it fit the antenna element length ? Because the quadrifilar element length (=infinite balun length) was shorter than 3/4 lambda length. Due to this fact I actually expected a higher resonance frequency, but it went out the opposite way.
FYI: The supporting of the elements is all done with PVC tubes, to avoid any metal influence.
Kind regards,
73 de PE1RAH, William Leijenaar --- _______________________________________________ Sent via AMSAT-BB@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