[time-nuts] GPS Interference Question

bg at lysator.liu.se bg at lysator.liu.se
Fri Sep 30 17:20:59 UTC 2011


Hi Chris,

> One sure-fire "fix" to the problem is to open up the military frequencies
>  to everyone.    GPS broadcasts on more than just the common L1 freq.
> but also on 1.2Ghz.

It is not military frequencies, it is military codes, the spread spectrum
sequence is encrypted.

There are different generation GPS satellites. Older generations are still
on orbit, thanks to a working life of a decade or more. General
replacement strategy is to launch a new to replace a dying satellite.

The classic GPS signals available is

L1 CA    open signal
L1 P(Y)  has been sent unencrypted in P form in the past, now encrypted Y
L2 P(Y)  same as above

Even when encrypted there are relations between the signals enabling
geodetic quality receivers to make measurements on L2 too.

With the GPS IIR-m satellites a new open signal on L2, called L2C is
broadcasted. We have 8 IIR-m on orbit now. [1]

We have one IIF satellite in the constellation, adding also an open signal
on L5.

> Again, not really pratical because of the huge cost of conversion

It will be interesting to see if consumer GPS receivers will do more than
one frequency. Perhaps interference on L1 will make that happen. ;-)

[1]  ftp://tycho.usno.navy.mil/pub/gps/gpsb2.txt
--

    Björn




More information about the time-nuts mailing list