[time-nuts] GPS Crystal Frequencies

Jim Lux jimlux at earthlink.net
Tue Oct 27 19:22:03 EDT 2015

On 10/26/15 7:06 PM, Brooke Clarke wrote:
> Hi:
> I understand 10.230 MHz since when multiplied it gives 1176.45,1227.60,
> 1381.05 & 1575.42 MHz, all GPS carrier frequencies.
> http://www.prc68.com/I/DAGR.shtml#GPSs
> But I've got a number of GPS receivers that have Rakon unit oscillators
> with a frequency of 10.949297.
> http://www.prc68.com/I/DAGR.shtml#Polaris_Link
> What's the story?

you might choose a frequency that when used as a direct sampler, causes 
the GPS signal to alias to a convenient offset frequency (then all 
Doppler shifts wind up being positive, for instance).

try 38.65 MHz for instance, that makes both L1 and L2 alias down to 
around 9.2 MHz, which is slightly less than 1/4 of the sample rate, and 
nicely accommodates the bandwidth of the signal

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