[amsat-bb] Helical Antenna for 2-meters
cwo4mann at comcast.net
Wed Feb 8 00:45:27 UTC 2017
I just finished assembly of the Cushcraft cross-polarized yagi which I bought from a fellow Ham. It was like new. Now I remember what I really didn't like like about that Antenna. I put one together back in 1978 or thereabouts. Putting the phasing harnesses on was quite the job! I managed to remember curses in four or five different languages (tnx Army language school). Anyway it's all together and I mounted it vertically on a 10 piece of pvc pipe for testing. SWR was almost 1:1 over the range 432.5 to 437.0 then rose slightly as I approached 437 MHz. I'm a happy guy now. Next project is either the 2-m Helical we've discussed here, or two 3-element yagis with circular polarization. I already have the yagis, so that would be a no cost option.
Sent from my iPad
> On Feb 7, 2017, at 18:23, Edward R Cole <kl7uw at acsalaska.net> wrote:
> Just scale the dimensions proportionally (except wire diameter);
> ratio = 144/435
> I built a 14 turn 437 MHz helical back in 1996 to receive the MGS beacon and built a 2.4 GHz 6-turn helical for 33-inch offset dish feed for AO-40. Plenty information in Amsat Archives. Original Kraus-W8JK design is optimistic in gain calculation.
> W9EK had good construction hints in prior publications.
> For receive-only do not sweat getting a good SWR. I used a 1/4 wavelength long 1/8 inch wide brass strip, run from connector to beginning turn of the helix for impedance matching. Space the point of connection to the helix about 3/16 inch above the ground plane reflector. Natural impedance of a helix is 140-ohm.
> On air experience with the 432 helix was that a ten element CP crossed element yagi is better. But if you desire CP the helix is a natural, though not perfect.
> 73, Ed - KL7UW
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