[time-nuts] Orbiting crystals

Magnus Danielson magnus at rubidium.dyndns.org
Sun Jun 28 19:35:05 EDT 2009


iovane at inwind.it wrote:
> James Lux wrote:
> 
>> Ah.. That's easy.. Pretty much every satellite in orbit derives its transmit
>> frequency from a crystal oscillator, either a TCXO or a OCXO.  So all you
>> have to do is pick a LEO satellite that is easy to receive and measure the
>> transmitted frequency, and that is at a frequency where other effects won't
>> dominate (ionospheric uncertainties, for instance, probably rule out VHF and
>> UHF downlinks).   
> 
> Hi James,
> 
> that's easy for you at Nasa! You have rotary antennas, good receivers and so on...
> I thought to GPS sats because there are cheap receivers all around, and hoped 
> the 1 PPS would tell something, so freeing me from considering doppler, relativity etc.
> 
> Anyway, please let me know if you find any easily detectable signals that doesn't 
> require a tracking antenna.

GPS will not help you at the PPS level, but you can avoid the tracking 
antenna anyway. The doppler-stuff and alot of other things is very well 
described. It is not hopeless, but not a very easy feather out of the 
hat thing.

Cheers,
Magnus




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