[time-nuts] GPS 18 behavior

[David J Taylor]

From: Jim Lux
[]
Oh, I didn't actually think it would be 10% off.. more like a few ppm,
depending on temperature.  I was wondering more what would happen if you
were indoors for a couple days, then went back out, what the box does.
realistically, I don't expect that it smoothly brings it back into line,
rather, I would expect it to "jump" to the correct time and timing.

I think, realistically, I should be looking at the actual sentences
coming out and figuring out whether our "GPS synchronized" state has
changed, and maybe deal with it appropriately.
=====================

Jim,

My experience is limited, but I recall that the PPS stopped soon after the 
signal disappeared, and would only re-appear when the unit had sufficient 
lock on the GPS.  There is indeed a valid/not-valid bit in the output stream 
(perhaps referring to position, it's in the manual).

My GPS 18x LVC is noticeably more sensitive than the GPS 18 LVC, and will 
work almost all of the time indoors.  I am on the second floor of a two 
storey house, and I have the 18x up against a south-facing brick wall 
perhaps 5m above ground level.  Most of the other GPS devices I have which 
work from puck antennas get satisfactory reception indoors as well.  Only 
the old Garmin GPS 12XL and a Rapco 1904M GPSDO need more attention to the 
signal - they are both turn of the century devices IIRC.  More modern 
devices seem to be more sensitive.

You might like to go for an 18x and put it in view of the sky, if possible, 
or even use a module like:

  http://www.adafruit.com/products/746

which works nicely indoors here as well, that particular unit being in a 
walk-in cupboard with a north-facing wall.  I'm at 56 degrees north, so you 
may be better located.  Perhaps that module may be more in keeping with your 
other devices?

Cheers,
David
-- 
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor at blueyonder.co.uk