[time-nuts] Building a GPSDO & trouble using Jupiter-T

bg at lysator.liu.se bg at lysator.liu.se
Wed Feb 1 09:47:34 UTC 2012

> On Tue, 31 Jan 2012 16:29:07 -0800
> Chris Albertson <albertson.chris at gmail.com> wrote:
>> I'm pretty sure those GPS recievers that send out more frequent data,
>> at say 2Hz or 5Hz are just interpolating.  It is not more accurate.
>> The GPS sats only send a frame once over 6 seconds.
> As Magnus already wrote, once you have a fix, you can use code tracking
> to get an updated fix up to rates of 1kHz. If you use codeless P(Y)
> code tracking or carrier phase tracking you can get even higher rates.
> But, you can only update an already available fix, not calculate
> a fresh fix from scratch at that rate. This is because carrier phase
> and codeless P(Y) code tracking has an ambiguity of the phase, which
> has to be first resolved by a "conventional" fix. Once you have this,
> you can use those two techniques to get fixes at high rates.
> 			Attila Kinali

The classic GPS receiver architecture use early and late correlators to
track the correlation peak. You can make fresh single fix solutions as
quick as your hardware can cope. However the correlator tracking loops
have a limited bandwidth - 5 to 25Hz-ish. It is of limited interest to
sample quicker than some 10-40Hz.



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