Re: which frequencies of radio waves does GPS use?

Greetings:

Back in the 1970s, one of my first projects as a research engineer was to 
manage a program for the development of atomic clocks for use in the GPS 
system. The program was very challenging for GPS was the first system that 
had to consider the effects of the Theory of Relativity. At that time we 
never dreamed that the GPS system would eventually be used by the general 
population for many purposes including navigation for automobiles, 
backpackers and would even be used to measure the shift in mountains here in 
California after earthquakes. After the Northridge earthquake, Oat Mountain 
in the San Fernando Valley was measuerd by GPS to have moved upward and 
sideways a total of 46 cm (18 inches).

Definitions: 
Hertz (Hz): the symbol for cycles per second
Megahertz (MHz) : symbol for  million of cycles per second.
Subcarrier, and modulation : techniques for placing information on carrier 
frequencies.

The GPS satellites transmit at microwave frequencies in what is named the L-
band, on two carrier frequencies, called L1 and L2. 
Carrier frequency L1 =  1575.42 MHz
Carrier frequency L2 =  1227.6 MHz.

The GPS signals are contained within two frequency bands 20.46 MHz wide (+/- 
10.23 MHz) centered about L1 and L2. The navigation information from each 
GPS satellite is transmitted on two subcarrier frequencies modulated on L1 
and L2.

 One subcarrier operating at 10.23 MHz uses a high precision secure code 
for military navigation systems.  The second subcarrier operates at 1.023 
MHz in an open code for less precise navigation for general use. The open 
code distance resolution is about 10 times greater than the military code 
resolution.

Because of relativistic time shift effects that were predicted by Albert 
Einstein back in 1910, the GPS satellites and their atomic clocks age more 
slowly than similar clocks on earth (this is some times called the twin 
paradox). This relative time shift is off set by setting the clocks on the 
spacecraft to run slightly faster by 0.0045674 Hz. 

For most of the 20th century the concept of time shifting and time travel 
was an esoteric effect used by science fiction writers. Today the atomic 
clocks in the GPS satellites are growing old less slowly than us here on 
earth in a measurable way and we must compensate the navigation information 
for this continuous time shifting!

References:
1) U.S. Coast Guard GPS Navigation documents.
 http://www.navcen.uscg.mil/gps/geninfo/gpsdocuments/icd200/
default.htm

2) A GPS primer on how the system works presented on the Aerospace 
Corporation web site at:
 http://
www.aero.org/publications/GPSPRIMER/index.html

Best regards, Your Mad Scientist
Adrian Popa