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mode-S (S1 and S2) reception in DL



Over the weekend I received the two (in DL) available Mode-S
transmissions from AO-40.

First reception was S1 EB on 2400.600 MHz on Dec 2,
0812UT - 0842UT, quite accurate on frequency (including 
doppler) with about 15 dB over noise. Typical QSY with
10sec period (magnetorquer) was observed.

Second reception was S2 beacon (2401.350 MHz) on Dec 3,
0818UT. I almost missed this turn, though I noticed the 
switching on the 2m beacon. But because of lack of 
live telemetry, I started receiving on 2400.600 MHz, with 
no sucess (of course..). Very puzzled by this (something 
wrong wired in shack??) I consulted the AMSAT-BB, and 
fell over the notice about the S2 beacon being turned on.
I was quick enough to copy some 15 seconds of the S2 Beacon
approx 5db weaker than yesterdays S1 EB. If I assume, that 
my converter didn't changed LO frequency in the last 24h, I
guess that S2 beacon is approx. 15 kHz down the 2400.350 MHz,
(I calculated doppler as -25 kHz and received around .310 !)
but this is only a guess, as I was too late for further 
investigation (beacon switched off.. grr).

Receiving system was a 1.6m (5ft) dish with preamp after 
2m H100 coax.. the converter was then located in the shack,
this enabled me to test some available converters, one 
homebrew from AO-13 days, one from SHF-Elektronik/Germany,
and the new UEK-3000 from SSB electronic Germany. All 
three were comparable with the UEK-3000 having the biggest 
gain, I suppose because of being designed for long cabling.
(S+N)/N was equal on all three as expected, as the preamp 
was mounted on the antenna.

So with the non-optimal squint angle from AO-40 I am really 
looking forward to working on Mode-LS! I the meantime I 
have to get my L-uplink working..

Have fun on AO-40, especially on the microwaves!

73s Achim, DH2VA




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