If you want this straight from the spec, grab a copy of IS-GPS-200J (it's free, just google it), look at section 3.3.1.1, which talks about the carrier frequenc

If you want this straight from the spec, grab a copy of IS-GPS-200J (it's free, just google it), look at section 3.3.1.1, which talks about the carrier frequencies of the various signals. From that: "The carrier frequencies for the L1 and L2 signals shall be coherently derived from a common frequency source within the SV. The nominal frequency of this source -- as it appears to an observer on the ground -- is 10.23 MHz. 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 (delta f)/f = -4.4647E-10, equivalent to a change in the P-code chipping rate of 10.23 MHz offset by (delta)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." In this context, "SV" is "Space Vehicle", a.k.a. a GPS satellite. You also have to make a relativistic adjustment in the user segment (aka "your GPS"). You can see an example of doing this correction in open-source software GPS receivers, for example https://github.com/jks-prv/Beagle_SDR_GPS/blob/de895035e93ba1b1b5b8f58df4149c32a4cdbfde/gps/ephemeris.cpp#L188 https://github.com/jks-prv/Beagle_SDR_GPS/blob/de895035e93ba... . This adjustment is documented in the above spec, in section 20.3.3.3.3.1 (which you'll see is almost verbatim copied into the the code linked above)