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Re: PSK-31 Satellite Donwlink Opportunity?



On Sun, 25 Feb 2001, MCGWIER ROBERT wrote:

> You have forgotten the contribution to Doppler caused by the uplink....
> Even with an inverting transponder, this will be a difficulty.
> 
> If it is a mode A (2m up and 10m down),....

You missed the fact that I said "inband" "inverting" transponder.  THus
uplink on 28 MHz and downlink on 29.4.   THe resulting Dopplers subtract
from each other and the only difference is the diffeernce in their
frequency.  With a 1.4 MHz split, this results in I think it was 45 Hz
total doppler...

> it is an inverting transponder to remove some
> of the Doppler,  you will still have over 2 KHz
> maximum Doppler offset.  Sorry!

Yep, that is the whole challenge to make it "inband" so as to avoid that
problem... 

> > 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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