[time-nuts] A "Short but sweet" Reply

Lux, James P james.p.lux at jpl.nasa.gov
Tue Sep 2 12:56:42 EDT 2008



Jim L...There is a handful of Amateurs that have quite successfully detected the Telemetry Signals from both NASA and ESA space probes currently roaming space, the idea is to simply detect these feebly weak signals, that's the aim, trying to copy telemetry and things like pictures is a long shot considering the digital nature of transmissions these days.


--- It's somewhat challenging (except when they're doing initial commissioning when the s/c is close to earth, so there's a huge signal, although with a s/c which has a big antenna (and small beamwidth), it would have to be far enough away that you're in the foot print (or you can be close to where they happen to be pointing it).
As the link you gave shows, it's certainly possible.

--- as for actually demodulating.. That's a bit trickier, but not too bad.  You know the general data format (because it follows CCSDS standards), so all you have to do(?) is build a suitable carrier tracking loop and the subcarrier demodulators (or for medium and high rate, where a subcarrier isn't used, a regular old PSK demodulator).  Then, you'll need some sort of logic to recognize the beginning of the frames, etc..  If you can receive transfer frames, you'll be doing quite well.  As for what's in the frames, I'm not sure what's published and what's not (there's all manner of ITAR and such that needs to be considered when you start talking those details)

--- A lot of it is in a book called 810-5, which is available on the JPL website. http://deepspace.jpl.nasa.gov/.  The link parameters are something you can probably figure out for yourself (EIRP, etc.)



If you visit this site, http://www.uhf-satcom.com/ or more directly this link, http://www.uhf-satcom.com/mro/ you will see what I attempting to do, there is a Block Diagram showing the basic system setup required, I have pretty much everything I need I've just got to put it together. Joseph Ruggieri often has microwave items for sale on eBay that's where I got my "Brick" from, Joe currently has some items on eBay but I don't think he has any of the PLO devices left, one can always ask.


----  You can build a receiver a lot of ways.  And a lot depends on what you want to do with it.  If all you want is to see the carrier, then you're not going to need totally awesome performance, so probably any old receiver will work.  Another interesting signal to look for is the radar from QuikScat at 13.402 GHz.  It's got a PRF of a couple hundred hertz, and it can be detected with a LNA and a spectrum analyzer, if you know when and where to point the antenna.

Jim Lux



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