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Re: AO-40, K-band Tx Test Successful!



Dear AO-40 fans,

Regarding the equipment used by G3WDG/G4KGC and myself for the 24 GHz
tests
on AO-40: Charlie and Petra were using a 22 x 18cm sized offset dish
with
linear polarisation feed. The noise figure of the preamp is claimed to
be
1.6 dB. The dish f/D is 0.6. My own equipment consisted of a 60 cm prime
focus dish with my 24192 MHz terrestrial transverter mounted onto it.
The
image rejection filter was retuned to cover both 24192 and 24048 MHz
simultaneously without degrading system noise temperature or image/LO
rejection. Charlie estimates his clear sky/sun noise ratio as about
2 dB. My measured overcast & rainy sky/sun noise ratio was 3.2 dB with 
1.4 dB of similar "coolish" sky to ground ratio noise. My own noise
figure
is about 2.5 dB (including waveguide runs and waveguide TR switch).

Measurement results indicate very good frequency accuracy after about
an hour from switch-on. The error in the beginning was about 30 kHz 
dropping to around 6 kHz at the end of the tests. Reception equipment
is very stable and accuracy is within +- 5 kHz, possibly much better.

My G/T is not very good, because of my dish still bearing the original
lossy sidelobe attenuation collar and absorbant. All things considering,
it is amaizing how well signals could be copied from 62000 km out :-)

Circular depolarisation would induce an extra 3 dB + of loss :-(
Ideally, the spacecraft would be in the 3 axis stabilisation mode, so 
that we would not have such a severe spin modulation to cope with.

Signals were very good anyway, with the Middle Beacon peaking 10 dB out
of the noise. There are a couple of my test result plots publicly
available
at: http://www.amsat-dl.org/journal/adlj-p3d.htm#NEWS

Now it is possible to test the S band receivers ;-)

Regards,
Michael, OH2AUE

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