Re: [gpsd-dev] Parallel build broken?

[Gary E. Miller]

Yo Hal!

On Mon, 25 Nov 2013 23:40:22 -0800
Hal Murray <address@hidden> wrote:

> Thanks for digging out the details.
> 
> address@hidden said:
> > The real reason it "finds" the satellites is that modern GPS units
> > have enough correlators to "listen" to all the SVs independently at
> > the same time, so it doesn't have to find anything at all. 
> 
> I think it's more complicated than that.

Well, yes.
 
> You can't listen to a SV unless you know where it is and (roughly)
> where you are so you can compute the Doppler shift to determine what
> frequency to listen on.

No.  ALL GPS sats trasmit on 1575.42 MHz, and 1227.6 MHz for L1 and L2,
IS-GPS-200G, section 3.3.1.1.

Most non-military GPS only listen on only L1.

What separates one SV from another is the code phase (correlation).

> > In fact any modern receiver can get fix right from the cold start
> > in few seconds if ephemeris data is uploaded to it from some
> > external source (e.g. from the Internet, "AGPS solutions"). 
> 
> Again, that assumes you know roughly where you are and the time so
> you can calculate where the satellites are so you can figure out what
> frequency to listen on.

Not frequency, code phase.

RGDS
GARY
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Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97701
        address@hidden  Tel:+1(541)382-8588

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