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PSK-31 Satellite Donwlink Opportunity?



Satellite and PSK-31 builders...
There may be an opportunity to fly a PSK31 Satellite 10m downlink
on a satellite in the next several months.  On 10m the total doppler is 
less than 600 Hz...  So users with a FIXED tuned 10m SSB receiver
could easily copy 20 or more QSO's without tuning for Doppler.
 
To calculate the minimum downlink power needed, I need to know practical,
(not theoretical) values for current implementations...
 
1) What is the "typical" noise level on 10 meters with a 1/4w vertical?
2) What is the minimum actual SNR required by most PSK31 decoders
3) What is the effective noise bandwidth of most PSK-31 implementations?
4) What is the gain (- dB) of a 38" dipole matched to 10m.  Thats
   the only antenna we have on the satellite that could be used...
 
With the new PSK-31 software that can actually MONITOR 20 simultaneous
QSO's in real time (W1SQLPSK), whole new concepts in Amateur Radio
COmmunications are opening up...  But in such wideband code, I guess the
narrowband  (55 Hz?) processing gain still applies to each channel?
 
My first cut assumptions for these unknowns might be 15 dB sky noise, 6 dB
SNR required in a 60 Hz bandwidth using a -12 dB gain antenna...?
 
On this short fuse experiment, we would simply put 20 PSK-31 audio
streams into a single UHF FM uplink having an onboard wideband (no 
doppler) receiver.  THus, the only doppler is the small 600 Hz
experienced on the 10m SSB downlink.  The PSK-31 software on the ground
can EASILY track this, since ALL QSO's move together!
 
This is ONLY an experiment to demonstrate the practicality of the
low power, low doppler 10m downlink for possible future designs
of an INBAND-INVERTING PSK-31 transponder that would have hardly
any doppler at all (45 Hz?).  Again, this experiment is designed to
VALIDATE the downlink, not to be a practical TRANSPONDER for general
QSO's, since its single wideband FM uplink requires pre-combined signals
for uplink from single participating ground stations.

But it IS  a free opportunity to maybe fly this experiment and show the
power of PSK-31 and sound card software to bring Amateur Satellites to
more people...  It could easily be used (as is) for distributing multiple
simultaneous amateur radio bulletins...
 
Even as is, dedicated ground stations in each of the amateur radio
countries could collect streams of PSK-31 data from schools, clubs
and many sources to uplink for everyone in the footprint to receive..
This collection could be via the Internet or a variety of other
means.
 
I already have the wideband FM UHF receiver so All I need is someone
to build the small 30 milliwatt or so SSB exciter for 29.4 MHz.
THey should be able to build it in a few inches of space...  My
UHF receiver is about the size of a large postage stamp...  We would
use an audio baseband of about 2 KHz.
 
I cannot promise anything, but at this point, it looks like we may
have some spare payload space on a satellite that is only 6 months away
from launch, and I would sure like to use it for a meaningful experiment.
And I think it is time to try this new narrowband, user-friendly 
mode... and demonstrate the value of 10m downlinks for their low doppler
and low satellite power potential.
 
de WB4APR, Bob



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