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Re: PSK-31 Satellite Donwlink Opportunity?



I added a sketch of the INBAND-INVERTING 10m PSK satelite transponder to
my CUBESAT Ideas WEB page:

http://web.usna.navy.mil/~bruninga/cubesat.html

By using a single 19.24 MHz XTAL we can get a 28.3 MHz uplink and 29.4
downlink using a standard 9 MHz xtal filter with less than 25 Hz doppler
throughout the pass. Well easy enough for manual tracking.  Less than 20
milliwatts could handle 20 QSO's in a 3 KHz bandwidth..

Now is 20 mW enough? Here is a first guess at the power requirements:?

1) Most existing 10m downlink satellites are successfully using about 30
mw per Khz of transmitter power.. for SSB and CW and Beacons (but the full
xponder bandwidth is never full to 100%, so most users get realatively
more power than this number would suggest)...

2) Using a standard 3 KHz SSB receiver and PSK-31 DSP and if there is no
other strong signal in the passband, then we can use a noise power
bandwidth of 60 Hz per user?

If so then I calculate a decodable PSK-31 downlink using less than 1
milliwatt per user!  Can this be true? 

Further the user on the ground will be transmitting with 25 Watts (Radio
Shack 10m rig) so the Uplink is 40 dB stronger.  Thus T/R isolation of the
inband transponder only needs to deal with a 30 mW transmitter and a 20 uV
sensitivity receiver..  Or about 95 dB of isolation over 1.1 MHz... 
Now.... How do we get that?  

de WB4APR, Bob




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