[time-nuts] Compensating phase differnces in dual frequency GPS receviers?

Attila Kinali attila at kinali.ch
Thu Dec 1 08:37:52 EST 2011

On Wed, 30 Nov 2011 19:56:25 -0800
Peter Monta <pmonta at gmail.com> wrote:

> Hi Attila,
> > [ L1 / L2 timing differences ]
> > How do dual frequency receivers deal with that?
> I've also been toying with the idea of an inexpensive dual- or
> tri-band GPS SDR, especially since there are now quite a few
> satellites emitting L2C, the civil L2 signal.  (Though I'd still like
> to try my hand at the fancy L2 semicodeless schemes.)
> I think that manufacturers calibrate out the timing differences
> between channels (as well as group-delay variations within a channel).
>  There must be some remaining error, though, e.g. over temperature,
> depending on the filter technology.

So, that'd mean there would be an automatic calibration system inside
the device, because i dont have any equipment with which i could
calibrate delays over a temperature range.

> ObTimeNuts:  There's an interesting recent thesis on GPS for time and
> frequency metrology:
> http://www.ptb.de/cms/fileadmin/internet/fachabteilungen/abteilung_4/4.4_zeit_und_frequenz/pdf/Feldmann_2011_Dissertation.pdf
> Section 5.1.3 has a few words on exactly this channel-filter-delay
> issue.  The author measures a coefficient of 20 ps per degree for a
> pair of receivers.

Nice disertation, but i cannot see how you come to the conclusion
that this temperature coefficient is from the input RF chain.
The measurement shows only a general time shift of the whole device.
And the author does not draw any conclusion from it.

			Attila Kinali

Why does it take years to find the answers to
the questions one should have asked long ago?

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