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Hı, Does gps l2 frequency signal, carrying p code, can be used without permission of US. If not how dual frequency gps receiver decrypt p code. I mean what is authorization process software or hardware? Thanks.

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You can attempt to use the P code without permission.

Unfortunately it is encrypted, with what is known as the W code, to produce the actual transmitted Y code. This prevents full use of its increased precision.

Fortunately, the W code is applied at a different rate to the P code, which allows some intelligence to be gleaned from the signal without knowledge of the W code, and this method is actually supported officially. See the wikipedia article for links out into the documentation.

At a quick scan (correct me if I've got this wrong) it appears that although this semi-coded approach will not allow you to use the 10.23Mb/s chip rate precision, it will allow some L1 to L2 correlation to estimate better the variable delay due to ionospheric propagation.

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  • \$\begingroup\$ Worth to know: End of 2018, GPS SV are 13 from block II R and 19 from block II RM or F. The two latter broadcast civil signal L2C (L2CM moderate, L2CL long) in phase quadrature, while P(Y) code is still sent in phase. Block II F SV also broadcast civil L5 on a 3rd frequency. Signals. \$\endgroup\$ – mins Dec 1 '18 at 14:03

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