[time-nuts] carrier phase tracking GPS receiver

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Mon Feb 19 18:59:41 EST 2007


Didier Juges wrote:
> Magnus Danielson wrote:
>   
>> You can acheive much greater speedup by a combined frequency/phase approach.
>> You will get a very accurate frequency error estimate, so you will very
>> quickly be close enought to go into phase lock. At least if your clock isn't
>> too noisy. So, the lock-in time should not be the major concern, but rather
>> the behaviour of the full setup when running. Also, another classic trick is
>> to vary the bandwidth, so you have a much wider bandwidth in the beginning and
>> then step down towards your target bandwidth as some suitable conditions have
>> been met prior to the step.
>>
>>   
>>     
> My concern is that closing the loop faster by itself does nothing, if it 
> is not stable enough. What I meant by being able to close the loop 
> sooner was that the carrier phase data is actually better than the OCXO 
> sooner after power up. I think you or Bruce said the Allan variance of 
> the carrier phase signal could be as good as e-10 in 1 second, or 
> something like that.
>   
Didier

Typically with a good local oscillator you can do even better than that, 
around 1E-11 in 1 sec is achievable and has been achieved.
Even with the on board TCXO typically 3E-11 or so in 1s is achieved.

Bruce





More information about the time-nuts mailing list