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AO-40 beacon results from VK4



I thought I would report on my findings when listening for the AO-40 Beacon
last night. The equipment is an unmodified Austar MDS downconverter/LNA, the
only thing I have done is sawed off the internal pcb antenna, and connected
a 3 turn helix straight to the first amplifier stage. The antenna is a TVRO
2.4M mesh dish, set up for Clarke Belt tracking with one actuator, the 2.4
Ghz LNB being cable tied to the existing C band LNB (to the top of it so as
to give an estimated 5 degrees offset).
As the bird came over the horizon at approx 08:35 UTC, my antenna was
totally in the wrong position (vert), but I could just hear the beacon, dur
to the fact that the satellite was very close r(range 6000km and closing). I
moved the dish around a bit, but still a very weak signal, no hope of
decoding it.
By about 9:00 UTC the elevation had risen to approx 40 deg and azimuth 6
deg. It was getting stronger, but still no signal strength on my FT736.
I decided to tweak the elevation, went outside and took a few turns off the
elevation bolt, (I thought abt 5 deg down on the dish), and what do you
know? The signal BOOMED in. S-7 above the noise. The only problem was the
fading, up and down like a yo-yo.
At abt 11:00 UTC range of 33000KM I still had an s-6 but lots of QSB, plus
the signal seemed jittery, not just from doppler, but seemed unstable.
It was very hard to get any blocks with valid CRC. I did get lots of non
valid blocks though. Noise level on the FT736 was S-0 by the way. Frequency
450.280 (downconverted I/F)
I ended up collecting data till abt 1300 UTC when the XYL screamed at me to
come to bed or else! Range was approx 48000km and I was still getting some
valid blocks , the strange frequency shifting had stopped, signal level abt
s-3 with lots of QSB still.
I have a question, why is there so much QSB on the signal, also, how do I
calculate the squint, and how does this relate to the signal?

Cheers all, happy telemetry gathering!

John de VK4JWT

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