[amsat-bb] Re: Arrow antenna reconfiguration results - UPDATE
ve9qrp at gmail.com
Fri Sep 25 06:53:05 PDT 2009
I really appreciate you doing this research for us. Two additional
ideas come to mind:
1. Those of us with FT-817s could configure its two RF ports to use
different bands and connect the rig directly to the beam's antenna
connectors, bypassing the duplexer. For this purpose, higher-quality
bnc terminated cable would be useful.
2. If I'm correct, your replacement duplexer is rather larger than the
one it is replacing. It would be a great topic for a Journal article
if someone with the necessary equipment and expertise were to design a
replacement with less loss.
On Fri, Sep 25, 2009 at 6:10 AM, Jeff Yanko <wb3jfs at cox.net> wrote:
> Hi all,
> A quick update to my new project to improving the Arrow antenna, efficiency
> wise. I wanted to see how well it would perform on gaining and losing
> access during AOS and LOS. AO-27 is not a good choice since the timer is
> turned on when it is well above the AOS horizon and it is switched off
> before it reaches its LOS horizon. That leaves a dependable AO-51 to test
> it out.
> With the last setup, the OEM diplexer provided by Arrow Antenna, I would
> copy AO-51 about 3 minutes after AOS and lose it about 3 to 4 minutes before
> LOS. Not bad, but people were saying they worked the birds when they were 1
> degree off of the horizon. I have some pine trees that could be an issue
> but they are spaced far enough apart that I can work between them and I also
> have to deal with the McCollough Range to the SSE of me here in Las Vegas,
> NV. Today, there were 2 passes of AO-51, one at 12 degrees elevation, the
> other at 74 degrees. During both passes, I began to copy the downlink about
> a 1.25 minute after AOS. A considerable difference from 3 minutes. The
> downlink also improved down to about minute before LOS. On the last pass I
> worked KG6NUB at 0124z and LOS was 0125z and my downlink sounded fairly
> good, though I was fighting desense. (That's another issue I need to
> resolve.) Also, on both passes, I never once lost the downlink. No
> dropouts or fades. I'm still amazed.
> Another issue I came across was how wide the beamwidth is of the Arrow
> Antenna between the Arrow diplexer and the new diplexer. I was wondering if
> this was going to happen and it did. The reason that this happened was with
> the old diplexer, the signal attenuated so much that you had to be pointed
> right smack dab on the bird, a few degrees off and you lost the signal.
> Now, with the new diplexer, you can point the beam in the general direction
> and still copy the bird. In most cases I had to turn the beam 90 degrees
> before I completely lost the downlink! Twisting the antenna to make
> polarization changes makes absolutely no difference now. This also
> attributes to the fact that now I'm copying the entire pass without dropouts
> or fades. Makes sense. What I've regained over the lossy diplexer makes up
> for any polarization differences, etc. for a better copiable signal.
> Next weekend I will have to try more passes and get a feel of how much this
> system has changed.
> Jeff WB3JFS
> Las Vegas, NV
> Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
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