[time-nuts] L1 and L2 frequencies

"Björn Gabrielsson" bg at lysator.liu.se
Thu Jan 15 13:55:39 EST 2015

> Brooke,
> The traditional GPS has C/A and P(Y) on L1 and P(Y) on L2.
> Most Civilian GPSes only uses C/A.
> Advanced receivers can also use P(Y) code, since the P-code is known,
> the hand-off to P code is known and the way that P-code is encrypted
> into Y-code is known (XOR with another code, called A-code or W-code in
> different sources). Modern receivers is able to do both code and carrier
> phase observations on the P(Y) code signals.

Read up on semi-codeless tracking, I dont think (pure) codeless is used


> The military goal of this "break-in" is not lost, as those receivers
> still rely on the C/A code and that is easy to jam. Also, the "break-in"
> comes at a signal quality loss and the advancement of methods have
> reduced this loss.
> The benefit of dual frequency observation is that ionspheric shift can
> be almost completely taken out of the error budget, adjusting both code
> and carrier phase observations. Then working on the integer ambiguity
> you can get carrier phase observations with accurate pseudo-ranges.
> Carrier-phase observations has a much higher precision to them, so that
> gives a very high precision and using a good reference network
> corrections can be adjusted to give good absolute position.
> If civilian receivers where to implement L2C and L5 which now is
> becoming common, they would gain quite a bit of precision in a similar
> fashion. For car navigation, the GPS would know which lane you are in.

There ARE civilian receivers doing this, and has been for quite some
years. And its not from only a few vendors - all the big ones have it -
Trimble, Novatel, Topcon, Javad, Leica, Septentrio and a few more. There
are now receivers tracking "GPS L1/L2/L2C/L5, Galileo
E1/E5A/E5B/AltBoc/E6, GLONASS L1/L2/L3, BeiDou B1/B2/B3, QZSS L1/L2/L5"

The price exceeds my home hobby budget, but so does a replacement CS-tube
a factory new OCXO based GPSDO and many other things you can sometime find
at reasonable cost used/recycled.



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