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
El 07/06/15 a las 04:10, Robert Bruninga escribió:
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.
Dear Bob,
Could you elaborate on this? If I understood correctly, position determination by means of Doppler measurements started with project Transit. With good knowledge of the satellite TLE and an accurate clock, a ground station could determine its position with good precision by measuring the Doppler curve from the beacon of the satellite over a couple of minutes or so. Indeed, two different frequencies were used to try and compensate for ionospheric refraction.
I think that this would work similarly and given good TLEs for PSAT and an NTP or GPS synchronized clock, it should be possible to locate ground stations just by measuring several of their transmissions over just one pass. Perhaps ionospheric effects on 10m are too high for this to work with much precision, but at least some rough estimate could be obtained (6 digit locator would be nice).
73,
Dani EA4GPZ.
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Daniel Estévez -
Robert Bruninga