[amsat-bb] Re: Arrow antenna reconfiguration results - UPDATE

Bruce Robertson ve9qrp at gmail.com
Fri Sep 25 06:53:05 PDT 2009

Jeff --

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.

73, Bruce

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.
> 73,
> Jeff  WB3JFS
> Las Vegas, NV
> DM26
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