Hi Rolf,
My understanding is that the material used for center pole in a helix doesn't affect the antenna dimensions or performance much at all. So, feel free to use whatever material you have handy that will work mechanically and environmentally (e.g. ice load and sun exposure). I've never made a helix for 70cm, but that's about a low a frequency as I'd consider. They get kind of large and unwieldy as you go down in frequency, and a 6" coil on a 7' boom would be pushing it for me. A crossed yagi could be mechanically easier to build, and, to Bob's point, you could make it run either polarity.
Good luck,
Greg KO6TH
Rolf Krogstad wrote:
I am new to satellites and new to the design requirements for UHF and am looking for advice.
I am looking to build a Helical antenna for the 70cm Band. I am considering the plans for such an antenna from the 2010 edition of the ARRL Satellite Handbook. The plans call for a 235 cm (7' 8") long, 2.5 cm (1") diameter center support made of either a wooden dowel which has been treated or a fiberglass tube. It also requires multiple 7.6 cm (3") spacers for the helical element.
My question is would fiberglass rods made of "Isophthlic Polyester Resin" be a good choice of material at UHF frequencies? I hesitate to use treated wood because I plan to mount this on the top of a 15 meter high tower and it isn't very accessible.
Thanks
Rolf NR0T [EN34] _______________________________________________ Sent via [email protected]. 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