Hi Ed,
On 07/02/2013 08:21 PM, ed breya wrote:
Here we go again - the first send didn't seem to get through. This is
the second attempt.
This talk of Costas loops reminded me of something I wanted to
investigate some day. I read somewhere a while back about carrier-phase
measurements, and various methods for recovering the GPS carrier
frequencies, including the Costas loop, and something with
carrier-squaring. Nothing I found showed actual examples or detail of
how this is done, only high-order mathematical descriptions.
For my needs, I'm more of a frequency-nut - I usually don't care about
getting time info, but I'd like perfect 10 MHz for reference. Can using
only the carriers lead to simple ways to get the same (or better)
frequency stability as a conventional GPSDO, but without the time and
location info, or is it pointless to worry about it, and just go with
full GPS decoding of everything? Or, is carrier-phase just an
enhancement only if you already have the full GPS info?
I know that the group could redesign the whole GPS system with tubes if
necessary, considering recent philosophical discussions on that, so I
think there's plenty of knowledge here about carrier-phase related stuff
too.
Just using the carrier phase in bare form isn't directly useful, as it
will be shifted in frequency by the doppler, creating a 1,57542 GHz +/-
6 kHz. If you decode the message (isn't all that much work) you get the
nav messaeg, the detailed orbits and can correct using that, but once
you got this far you could just as well do full nav message.
Cheers,
Magnus
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