[time-nuts] GPS clock offset frequency

[Magnus Danielson]

On 09/28/2010 11:54 AM, Alexander Mayer wrote:
> Can someone on this list provide me with a definitive engineering reference (not a second party academic assumption of the value) that provides the actual offset frequency of on-board GPS clocks set by the engineers?
>
> GPS ground clocks have a fundamental frequency of 10.23 MHz. The GPS satellite clocks are designed tick a bit slower, but exactly how much slower? Some references say
>
> 10.229 999 999 543 MHz (e.g., Ashby and Spilker, 1996)
>
> others say
>
> 10.229 999 995 43 MHz
>
> which makes more sense, but might not be right. A lot is riding on that extra 9 and I do not want to assume what the value is based on canonical thinking.

Definite reference for us civilians is IS-GPS-200E:
http://www.navcen.uscg.gov/pdf/gps/IS-GPS-200E_Final_08Jun10.pdf

Link found at
http://www.navcen.uscg.gov/?pageName=gpsReferenceInfo

Page 20 contains the answer:

The SV carrier frequency and clock rates -- as they would appear to an 
observer located in the SV -- are offset to compensate for relativistic 
effects. The clock rates are offset by f/f = -4.4647E-10, equivalent to 
a change in the P-code chipping rate of 10.23 MHz offset by a f = 
-4.5674E-3 Hz. This is equal to 10.2299999954326 MHz. The nominal 
carrier frequencies (f0) shall be 1575.42 MHz, and 1227.6 MHz for L1 and 
L2, respectively.

So, you will see that it has been further refined.

10.229 999 995 432 6 MHz

Thus, your Ashby and Spilker reference is off with a 9 too much, but the 
other references use the old ICD-GPS-200 value. The IS-GPS-200D has the 
value of 10.22999999543 MHz.

Cheers,
Magnus