[time-nuts] Speaking of Costas loops

[Magnus Danielson]

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