[amsat-bb] PSAT Doppler Science Project

Robert Bruninga bruninga at usna.edu
Sun Jun 7 02:10:54 UTC 2015

>  I was able to copy Psat  435 mhz downlink today...nice !
> Watching the stations move diagonally across the waterfall
> was an interesting Display of the Doppler on the uplink.

Yes, and you can draw that Doppler curve and from the rate of change  you
can calculate that stations position!

That was the basis for all Early Satellite Positioning systems and most of
the early EPRB Emergency Locator beacons.  It woiuld be a great science
project for kids to plot the doppper and see if they can figure out the
position of a station!

When authors start upgrading PSK31 programs so that they are fdull duplex
and can AFC their own uplink, then none of the satellite user signals will
slew, but since we chose the same uplink as normal terrestrial PSK31
users, those signals can plot a nice Doppler curve.  The only problem
there is that they turn their transmitters on and off, but usually stay on
the same 10m frequency, so that means although their signals are disjoint,
their emissions should all be on their theoretical Doppler curve and
therefore can be located.

Actually, on just one pass all you can get is a line of position relative
to the satelites track,  But on two passes, then  you can have two lines
of position and where they intersect is the stations position.

Good luck!  Maybe someone has the time to search for a good reference for
the technique.

Bob, Wb4APR
US Naval Academy

More information about the AMSAT-BB mailing list