[amsat-bb] Arrow antenna reconfiguration results - UPDATE

Jeff Yanko wb3jfs at cox.net
Fri Sep 25 02:10:24 PDT 2009

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


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