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Re: PSK-31 Satellite Donwlink Opportunity?



>  BB> This is ONLY an experiment to demonstrate the practicality of the
>  BB> low power, low doppler 10m downlink for possible future designs
>  BB> of an INBAND-INVERTING PSK-31 transponder that would have hardly
>  BB> any doppler at all....

Tony Langdon wrote:
> 
> The near zero Doppler is only true for (1) the uplinking station and (2)
> stations close to the uplinking stations.  Others will see more Doppler shift.

Duh...  Good observation!  Shucks, I thought it was too good to be
true...  OK, how about this solution...

Each TRANSMITTING station can pre-compute the Doppler for his UPLINK so 
that it arrives at the satellite with 0 doppler.  And since the worst
case doppler is less than 600 Hz, then  the 10m RF transmitter never needs
to be tuned.  The PSK-31 software simply slides the audio carrier within
the audio passband.  SImilarly, the DONWLINK then contains all downlinks
with 0 doppler.  THe DOPPLER at each receive site can now be accomodated
easily within the PSK-31 decoding software since it is still within
600 Hz so no RADIO controls are required...

OK, it takes a little more software, but still seems very easy to do
Thanks for pointing this out...

By pre-computing for 0 on the satellite, then, the position of each user
in the single 3 KHz downlink remains fixed making it easy to join or find
a QSO.   Also since all doppler comnpensation is only self relative, then
it is entirely doable within the PSK program...

BUT WAIT!  Maybe the PSK-31 would NOT EVEN Need a orbit model!  As
someone else suggested there should just be a single PILOT channel
with a unique RYRY sequence.  The PSK-31 RECEIVE software just looks
for that channel and then OBSERVES its offset.  Thus he now konws
everything he needs to compensate his uplink in the opposite direction...

Except for one thing.  He needs an absolute reference to start with...

OK..!  How about the BOTTOM 600 HZ of the transponder is reserved for
"seeking".  Each new USERs PSK-31 software, after it finds the PSK-31 RYRY
PILOT, it transmits its own unique code 600 HZ lower.  Then it SERACHES
the downlink to FIND it.  Once it finds its OWN signal, then it has
instantaneous real-time knowledge of the exact Doppler offset.  At this
point the software knows everything it needs and the "SEEK" transmission
is no longer needed.  Now the user is LOCKED ON and is free to join any
QSO anywhere in the passband.   And from this point on the PSK-31
transmitter and receiver can be fully tracked by simply observing the
drift of any, OR all OR JUST THE pilot.  It doesnt matter, because
everyone has 0 DOppler at the bird....

Wow...
Just a little software....

de WB4APR, Bob




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