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Dual-frequency civil GPS receivers (used chiefly by the surveying, geodesy,
and machine-control sectors) use special techniques to make measurements on
the L2 frequency. These techniques do not require access to the crypto codes.
These receivers are neither SPS or PPS receivers, per se. There's a wealth of
information on L2 tracking on the Web and in various publications. To get a
hint about L2 tracking, go to . Click on "Technology"
and then select "GPS L2 Tracking" from the list of technologies.
But the L2 situation is starting to change. The latest GPS satellite to be
launched, IIR-M-1, transmits the new civil L2C code on L2. All future GPS
satellites will transmit this signal too so that conventional code-tracking
techniques can be used to track these signals with civil L2-capable receivers.
-- Richard Langley
   Professor of Geodesy and Precision Navigation

On Tue, 6 Jun 2006, Peter MacNeil wrote:

>       Richard,
>   It's my understanding that civillian Recievers can only
>process the C/A    code in the L1 signal not the P(Y) code
>in the L1 and L2 Frequency?
>   That's why when I take my ship to sea, (where I expect to
>perhaps sail    outside of DGPS range) I actually load up
>the encryption code so that my    PPS receiver will process
>the P(Y) code in both the L1 and L2 carrier    waves,
>allowing for corrections caused by Ionospheric and
>Atmospheric errors.
>   Am I incorrect? Are currect SPS recievers capable of
>using the    P(Y) code?  If so, why is the "Crypto" still
>issued, and why does it make    a difference?  Any
>clarification you provide I'd like to share with my
>collegues...and I'm about to eagerly read your paper to
>which you provided a    link.
>   Thanks
>Pete
>   Richard wrote
>> The underlying P-code (before encryption with the W-code
>> to produce the Y-code) is the same on both L1 and L2 and
>> civil receiver manufacturers have for years used this
>>    feature in dual-frequency receivers to provide the
>civil
>> community with capabilties far superior to those typically
>> required in military applications. As an example, at UNB
>> we developed a machine control system with 2-centimetre
>>  accuracy.
>
>
>
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===============================================================================
 Richard B. Langley                            E-mail: lang@unb.ca
 Geodetic Research Laboratory                  Web: http://www.unb.ca/GGE/
 Dept. of Geodesy and Geomatics Engineering    Phone:    +1 506 453-5142
 University of New Brunswick                   Fax:      +1 506 453-4943
 Fredericton, N.B., Canada  E3B 5A3
     Fredericton?  Where's that?  See: http://www.city.fredericton.nb.ca/
===============================================================================

   

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