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I've been surfing the web for info regarding the GPS carrier

frequencies for you guys wanting to design and build your own

antennas. Though it sounds like a bit of a daunting task, the

following may help.



***********************



GPS Signals in detail



 Carriers



 The GPS satellites transmit signals on two carrier frequencies. The L1

 carrier is 1575.42 MHz and carries both the status message and a

 pseudo-random code for timing.



 The L2 carrier is 1227.60 MHz and is used for the more precise military

 pseudo-random code.



 Pseudo-Random Codes



 There are two types of pseudo-random code (see tutorial for explanation

 of pseudo random codes in general). The first pseudo-random code is

 called the C/A (Coarse Acquisition) code. It modulates the L1 carrier. It

 repeats every 1023 bits and modulates at a 1MHz rate. Each satellite

 has a unique pseudo-random code. The C/A code is the basis for civilian

 GPS use.



 The second pseudo-random code is called the P (Precise) code. It

 repeats on a seven day cycle and modulates both the L1 and L2 carriers

 at a 10MHz rate. This code is intended for military users and can be

 encrypted. When it's encrypted it's called "Y" code. Since P code is

 more complicated than C/A it's more difficult for receivers to acquire.

 That's why many military receivers start by acquiring the C/A code first

 and then move on to P code.



 Navigation Message



 There is a low frequency signal added to the L1 codes that gives

 information about the satellite's orbits, their clock corrections and other

 system status.



**********************



I copied this from a Trimble site which

has a very well written tutorial on GPS, with pictures and

animation for us "reading comprehension challenged" at



"http://www.trimble.com/gps/"



It's full of general info about the system and how it works

and they have made it digestible.

I'm sure there's other company's sites out there too, this

is just the first one I hit via Yahoo. Good luck with your

antenna design.



Dan Schaefer







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