[amsat-bb] Re: ARRL dual moxon turnstyle project questions
s.wilson at yahoo.com
Sun Aug 5 07:56:27 PDT 2007
Thanks very much for the feedback everyone.
>From what I was reading in the articles, I was under the impression that
a circularly polarized antenna was a step above linear polarized setups
such as the Arrow (or any small yagi) and verticals. In practice, I'm
having somewhat better luck with the linear setup. Until Bruce Mentioned
the short yagi/tv rotator setup, I hadn't even considered my own similar
setup as an option.
Here are my experiences so far:
My first attempt was with a 2m/440 mobile whip with a radial base. The
antenna was tilted over about 30 degrees to be slightly more
perpendicular to the predicted path of AO-51. From that pass, I could
definitely tell that I was tracking a satellite, but couldn't copy
anything that I was hearing. This was fed into my IC-7000 with about 15
feet of RG-8X.
Second attempt was receiving with just the 440 section of the dual moxon
antenna system. The closest I got with that was perhaps a little less
noise, but definitely no copy. Obviously, that's not inheriently a
problem with the antenna, but likely a problem with my implementation
which - which I can't really test. My antenna analyser only goes to uhf.
Bruce's email saying that a TV rotator and linear yagi's would be better
than a full blown system for a beginner contradicted what I had
convinced myself of - that I would be way too far down in the noise with
the fact that I was linear polarized and had no elevation control, and
with about 75' of less than stellar RG-58.
In fact, I have something usable right now on my roof: a cushcraft
2m/440 3 el vertical yagi on a tv rotator.
So far this has the best results to date. I've been able to copy at
least parts of call signs on the latest AO-51 pass, and managed to get a
pretty clear copy on a couple of CW beacon passes.
Now I'm considering incremental improvements.
I have a length of RG-213 that's been waiting to replace the radioshack
RG-58 feed to the yagi, so that should give me about 2dB.
I am hearing that a preamp is an absolute requirement. I'm now
researching the best method to feed the dual yagi.
If, after that, I can get a better copy on the passes, I'll try to make
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