GPS : Global Positioning System ₪ 1.1.2. The GPS-signal

 

The GPS signal is transmitted by the satellites of the constellation in the direction of the surface of the Earth.

It currently consists of two carrier frequencies :

L1 at 1575.42 MHz, and L2 at 1227.60 MHz, whose stability is ensured by otomic clocks. Theyn correspond to wavelengths of 19 cm for L1, and 24 cm for L2. They are generated from a frequency F0, called fundamental, at 10.23 MHz.

These frequencies are modulated by pseudo-random codes :

✽  C/A  code (Coarse/Acquisition or Clear/Access) modulating L1. It is accessible to all users.

✽ The P (Precise) code modilating 1.1 and 1.2 is only accessible to authorized users.

✽ And finally, the navigation message, at 50 Hz, which we present in the next paragraph.