[amsat-bb] AO-51 Mode VS observations

["Greg D." <ko6th_greg@xxxxxxxxxxx>]

Hi folks,

Just completed my first sucessful pass on AO-51 mode VS.  My equipment is as 
used for AO-40; a screen-lined BBQ grill dish with a 3 turn helix feeding a 
Khune preamp and a Drake 2880 downconverter which was modified for a 2100 
mhz LO.  I am using an Icom R7000 all-mode scanner for the +/- 200 mhz IF.  
Az/El rotor and uplink doppler are under computer control (Predict 2.2.1 
under Linux); doing manual control of the S-band downlink.  One hand on the 
mike, the other on the tuning knob!

Signals from AO-51 were a couple of S-units stronger than AO-40 ever was.  
Most of my operating on AO-40 was a solid S0, with peaks on close-in passes 
with good squint peaking at maybe S2.  Just on this one pass signals were up 
to S3-4 and full quieting, but with some fairly strong QSB.

The FM performance of the R7000 is less than wonderful.  Actually, to be 
blunt, the whole rig is stone deaf, but the need for a good SNR in order to 
work in the FM mode makes the need for a strong signal more critical than 
before.  So, the combination of signal strength, IF radio, and FM mode made 
for an only slightly better experience than with AO-40.  At 200 mhz, the IF 
is at the low end of the Drake's IF passband, but that shouldn't have been a 
factor.

One factor that I still need to account for is antenna positioning.  The 
rotor assembly moved a bit during this past winter's storms, and I really 
don't know exactly where it's aimed.  For most LEO work, it's easily close 
enough, but probably not with the Grill.  Next time we have some sunshine 
here, I need to re-aim things...

Thanks go to WA6DNR, K7MT, and N5UXT for putting up with my learning curve.

Greg  KO6TH

p.s.  The 19:35z pass just finished...  Signals were weaker than before, but 
QSB not quite as bad.  Peak signal at about S1.  This pass was lower than 
the earlier pass, but off to the west where I have a clean shot at the bird 
(no trees in the way).  Tried playing a bit with the antenna aiming, and it 
seems that I'm off by about 10 degrees in Azimuth.  Definitely need to 
re-aim.
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