[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 15:54:21 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. The reported signal
> strength and number of active satellites appears more consistent as
> well. The extra cable length meant that I could bypass a short BNC patch
> lead I had, so at least reducing the number of connectors.
Running this monitoring for a while is producing unexpected results. From
about midday yesterday to midday today, I reverted to the Garmin GPS puck,
to establish a baseline. On changing back to the new puck, the signal now
seems worse! The pucks are in approximately the same location - about 140
mm from each other - outside on a SSW-facing window, with rather more than
135 degrees of clear view.
This raises the question - how long should one monitor GPS satellites
(e.g. the reported number and strength) to get a good average value when
comparing pucks? I vaguely recalled the orbits being 12 hours, so I had
thought that one day would be enough. Any comments?
Thanks,
David
--
SatSignal software - quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor at blueyonder.co.uk
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