[time-nuts] Speaking of Costas loops (WAAS)

Jim Lux jimlux at earthlink.net
Sat Jul 6 16:48:39 EDT 2013


On 7/6/13 9:29 AM, Joseph Gwinn wrote:

>>> Code/Carrier Frequency Coherence: The lack of coherence between the
>>> broadcast carrier phase and the code phase shall be limited. The short
>>> term (<10sec) fractional frequency difference between the code phase
>>> rate and the carrier frequency shall be less than 5x10-11 (one sigma).
>>> Over the long term (<100 sec), the difference between the change in the
>>> broadcast code phase (convert to carrier cycles) and the change in the
>>> broadcast carrier phase shall be within one carrier cycle (one sigma).
>>
>>
>> This is interesting. Does it imply that they regenerate the code on board?
>
> Very unlikely, because then the bird would have to understand every
> possible code, including those not invented when the bird was launched.
>

the class of codes used is pretty restricted (e.g. Gold/Kasami codes 
with 10 bit generators), at least for GPS.  Most correlator and 
generator implementations are somewhat programmable, at  least as far as 
the tap configuration and the initial load.




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