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
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