[ntp:questions] Installing more stable oscillator?

David J Taylor david-taylor at blueyonder.not-this-part.nor-this-bit.co.uk
Sun Jul 15 05:41:36 UTC 2007


Pete Stephenson wrote:
[]
> I was looking at that as an option, but I was concerned about GPS
> signal strength in my area due to buildings and a limited view of the
> sky[1]. I was told that the GPS 18 LVC is a generally good unit, but
> that it's antenna reception was not fantastic in areas of marginal
> reception.

It is certainly not as sensitive as the active antenna on my other GPS 
system.  The latter will work indoors (at the top of the house, through 
the roof material) quite comfortably, whereas the GPS-18 needs a direct 
view of some clear sky.  At one stage, I had the GPS-18 just outside the 
window with a 50% maximum sky view:

  http://www.david-taylor.myby.co.uk/ntp/FreeBSD-GPS-PPS.htm

> How good is the GPS 18 LVC as a time source? From what I can read, the
> leading edge of the PPS pulse is within 1 microsecond of UTC, which is
> certainly more than adequate for my needs, but it's always nice to do
> better if possible. :)

1us is the spec.  On a very old 133Mhz/48MB BSD system, this is what I 
see:

  http://www.david-taylor.myby.co.uk/mrtg/daily_ntp.html

where the drift is when the heating comes on, and the odd spikes are (I 
think) lack of enough satellites.

Cheers,
David 





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