[time-nuts] How long to monitor GPS? (was: Re: Rapco 1804M - serial problems?)

David J Taylor david-taylor at blueyonder.co.uk
Fri Oct 21 16:50:35 UTC 2011

>>> I've now written a small plotting program to show the PDOP, satellite
>>> signal strength, inactive/coarse/fine lock mode etc.  This ideally 
>>> needs to
>>> run for several days with the box connected to each puck in turn, but
>>> preliminary results show that the unit achieved "fine" lock several 
>>> times
>>> with the new antenna, but never with the old.

> 24 hours should in theory be enough but 2 is not a statistically valid
> sample size.   you need more samples before you can say anything about
> the probability of locking.  How many depends on the size of the error
> bars you can live with.
> Chris Albertson

Thanks, Chris.  I just ran the GPS visibility part of my orbit prediction 
program (WXtrack), and it seems to show a very similar pattern from 
day-to-day, albeit with a slight time drift as the days progress.  So it 
looks as if the very first time I plugged the new puck antenna in we were 
just going into a maximum number of satellites visible phase.

Looking further it's about 4 minutes a day, so making me wonder whether 
the satellites are locked to a "sidereal" orbit (I expect that's not the 
right term!).

SatSignal software - quality software written to your requirements
Web:  http://www.satsignal.eu
Email:  david-taylor at blueyonder.co.uk 

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