[time-nuts] New GPS Signals

brooke at pacific.net brooke at pacific.net
Wed Mar 25 14:27:39 EDT 2009


Hi Magnus:

The reason F0 = 1.023 MHz is that it's also used as the basis for the data
bit rates.  The L1C/A code is 1 ms long @ F0 rate.
The L2CM (Moderate) code will be 20 ms long @ F0/2
The L2CL (Long) code will be 1.5 sec long @ F0/2,
so maybe F0 should be 511.5 kpbs?

I discovered that the Trimble p/n 16768-80 Trimpack GPS receiver has a
graphics capability, which none of the others have, and wanted to know
why.  So I'm in the process of reverse engineering and repairing it. 
There's still a power supply problem that's making the LCD extreamly hard
to read, but now I know the reason for the graphics is to switch between
English and Arabic for all the displays.
http://www.prc68.com/I/Trimpack.shtml#GraphicsTP

My interest in the GPS Link frequencies and codes is related to the
Polaris Guide (civilian version of the current military DAGR GPS receiver)
and possible firmware upgrades.  I've just got off the phone with Rockwell
and they say the Polaris guide only has L1 capability (I was expecting
that it also had L2 since the DAGR has L2).
http://www.prc68.com/I/DAGR.shtml#Pol
I'm in the process of adding a LF differential beacon receiver interface
to the Polaris Guide.  Also have the connector on order to add Have Quick
time fill to the O-1814 Rb Time and Frequency standard.
http://www.prc68.com/I/O1814.shtml

Have Fun,

Brooke Clarke
http://www.PRC68.com


> brooke at pacific.net wrote:
>> Hi:
>>
>> There are three new civilian GPS signals, L1C, L2C and L5.
>> http://www.prc68.com/I/DAGR.shtml#GPSs
>> The original civilian signal, L1 is at 1575.42 MHz (154 * 10 * F0,
>> F0=1.023 MHz).
>>
> f0 should really be set to 10,23 MHz.
>> L1C is at the same frequency as L1 but uses the code like Japan.
>>
> It looks similar to L5 actually, but coordination with Galileo, QRSS,
> Glonass and Compass is underway.
>> The new L2C signal is at 1227.60 MHz (120*10*F0).  Allowing for path
>> length corrections.
>>
>> The new L5 signal is at 1176.45 MHz (115*10*F0).  This is intended for
>> aircraft safety.  It also has the largest frequency difference to L1 so
>> should also be the best for determining the path length through the
>> ionosphere/troposphere allowing for a more accurate time fix
>>
> Currently we have these signals:
> L1 C/A (from all current sats)
> L1 P(Y) (from all current sats)
> L1 M    (from GPS-IIR(M) sats)
> L2C      (from GPS-IIR(M) sats)
> L2 P(Y) (from all current sats)
> L2 M    (from GPS-IIR(M) sats)
>
> In a couple of weeks we can also expect the first transmission of
>
> L5C    (from GPS-IIR(M)20 sat)
>
> It will be years before we see L1C (from GPS-III sats).
>> I'm hoping my Polaris Guide receiver will get upgraded firmware to get
>> these signals as well as have WAAS added.  See:
>> http://www.prc68.com/I/DAGR.shtml#Pol
>>
>> Are there any new timing GPS receivers that take advantage of the new
>> signals?
>>
> There is a few, but they are not in wide spread. You need to look into
> the geodestic receiver market. Trimble amongst others have receivers
> claiming support.
>
> Cheers,
> Magnus
>
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