[time-nuts] new gps sat prn30 svn64

Tom Van Baak tvb at LeapSecond.com
Tue Mar 4 23:46:17 EST 2014

"tom jones" wrote:
> I haven't rulled out dopplar shift or my mis-understanding of how gps works and what msg 30 really means.
> Perhaps the sat is broadcasting the bias and drift every minute and the gps receiver is dummer than I thought ?

I believe message 30 is about the local clock in the GPS receiver. This has nothing to do with the clocks in the GPS satellites themselves. The SV atomic clock bias and rate is reported by the a0, a1, a2 parameters. See SiRF message ID 14, 15, or 70 or the GPS ICD for details.

> prn clk bias clk drift 30sec drift   30sec clk bias  next orbit clk bias update & utc
> 01 5.419324e-07 1.939370e-1213 1.350894e-14  2.4980e-10 0714  3.056667e-08 0316
> 02 4.801467e-04 -6.812491e-13  -2.547918e-14 -7.5000e-12 1332 1.832122e-07 0619
> 03 3.292035e-04 -7.611533e-14  1.553618e-14  -2.2900e-12 1529 -1.075634e-07 150
> 14 5.685252e-06 -6.154375e-13  2.511121e-14  -8.2501e-12 1112 5.062425e-08 0459
> 05 -3.874342e-04 2.121078e-123 8.206977e-15  9.7660e-11 1433  3.457315e-08 0838

The second number is suspect: "1.939370e-1213" really? Since the table includes all 32 SV it looks more like ephemeris or almanac data than something to do with your receiver. Then again, clock bias and drift numbers (e.g., for prn 14) of 5.685252e-06 and -6.154375e-13 translate to 5.6 us bias and 5.3e-8/day frequency drift so that would certainly be a cheap quartz oscillator not an atomic clock. What SiRF message(s) did it come from?

I'll track down some of the other questions you've posted recently. What make/model SiRF receiver are you using? Internal or external antenna? What version of SiRFDemo are you using?


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