[amsat-bb] Arrow antenna reconfiguration results
wb3jfs at cox.net
Thu Sep 24 02:17:23 PDT 2009
After being off the air for about a month, I recently made some changes to
the satellite setup. I upgraded from the TH-D7A(G) HT to the TM-D710A
mobile dual bander. Yes, a bit bulkier, but worth its weight. Anyhow, I
know many sat operators use the Arrow antenna setup, like what I've been
using the past 7 or so months with great results. However, I've always
known that the diplexer that comes with the unit is reather lossy. From
some reports I've read as much as 2.65dB of loss. That's almost half of
whats being received or transmitted being thrown away. When I layed out the
new portable setup I made it an issue to "lose" the diplexer and put one in
line that would perform better. I purchased the Comet CF-416. It's loss is
about .26dB. A considerably less amount by far and if needed in other
applications it can handle more power than the 10 watts alotted for the
Arrow's diplexer. I also bought some good quality RG-58 coax, only 6 feet
in length, for both 145 and 440, so there isn't much loss from this. About
.6dB according to the data sheet.
After the assembly and installation was complete, on air usage was next.
AO-27 had a fairly decent pass to the east of the QTH with a max elevation
of 24 degrees. I've remembered how the passes sounded previously at this
elevation so I could get a mental comparison. As the bird's timer turned
the digital transmission on I noticed one thing immediately, the signal was
clearer and no hiss. The analog timer swtiched on and the voices became
copiable. The signal appeared to be a bit stronger than the old setup with
the Arrow antenna but the most remarkable improvement was from the time I
started to receive the signal to near LOS, it never once dropped out! It
almost appeared as though I changed my linear antenna to a CP with a preamp.
I figured this is too good to be true. I then decided to test it with AO-51
and see how well that bodes. I noticed I was copying the signal closer to
the horizon than the previous set up and again the same results with no drop
outs, except for the one time the house blocked the signal for about 20
So if anybody is considering improving their current Arrow antenna, please
do so by getting a better diplexer. They are not expensive, $40 to $60, and
of course some decent coax, short runs are better but give yourself enough
slack so you don't cut yourself short!
See you on the birds!
Las Vegas, NV
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