KE7KRY'S Dual Polarity Moxon
Addendum: 1/20/2007, Larrry today passed his tech/general written exam. Welcome KE7KRY, a new ham.
Inspiration comes from a variety of sources. That's a lesson I learned once again when the MoxonAntennaProject received an email about whether a dual polarity moxon was possible. As always when someone inquires about yet another moxon variant, I say "build it, let's see if it can be done."
Larry writes:(12/14/06) Steve,
Sorry to bother you with a Moxon question, but I've been reading a lot on Moxon and went ahead a built a tubular w/ 1/2" copper tubing and conduit boom to try (which seems to work pretty well). I was amazed at the SWRs across the band by the way! I've attached a 3D drawing of what I'd like to try...which is a dual polarity moxon. I cannot find anywhere that someone has built/tried it yet...only talked about stacking (which I'm not interested in doing yet).
Do you see any reason this wouldn't work? I know on yagi's and quads don't seem to be hugely affected by a dual polarity set up...and I'm hoping the Moxon is the same/similar. Any help/opinion/experience you'd be willing to share would be greatly appreciated!
Thanks in advance. Larry.
Dual Polarity Drawing
(1/2/07) Well I built the dual polarity Moxon. Attached you'll see some early morning pics (in a wind storm). It's sized for 10 meters and is a dual polarity 1/2" copper tubed Moxon...only 20' to the boom for now. Very broad banded and there was no noticeable difference between the single antenna and dual polarity. I've simply slapped it up against the shed for further testing and playing. So far it's proven to be as everyone else's tests have shown. Even at 20' I'm making some nice contacts.
I will mention that the calculator doesn't seem to take into account that the vertical polarity needs to be a bit shorter on the elements. No problem though, I simply put in a fictitious frequency and am good to go.
I play on 11 meters and listen to the rest (i.e. 160-10meters). I did in fact tune this for the upper 11 and 10 meters though. But I've never tested it on 10 meters, so I don't know exactly what the SWR's will bring...but can tell you this is by far the most broad banded antenna I've ever tried bar none!!! Maybe I did something wrong in the build because I constantly keep getting (with multiple meters to confirm) the same results;
Vertical side: 26.415MHz = 1.5:1 / 27.995MHz = 1.1:1 ( on the down slope)
Please keep in mind I have just over 100' of new Beldon RG8x and 3 watts...so there is some dB loss there. But even at the shop/office (where I built it) the readings were similar with 50'. Can this be true? Nah...it's too good to be true!!!
As far as the support mast, the spreader/isolator for the elements will sometimes touch the support mast. However, it's PVC80 and even with it touching doesn't affect the SWR's...or rather, I slid the boom up to where IF the wind takes the element and hits the mast (which it did in this morning's wind) it will affect nothing...which has been the case. I opted for outside separators so that I could slide/adjust them without problem, and to allow the beam to drain any internal moisture. I have been trying to think of what I can use as an insulator (plastic) that will attach to the beam and mast to hold it...but haven't gotten that far yet. That is one of the things I'd like to address. So far though, it's not been an issue.
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