[time-nuts] TruePosition GPSDO Holdover Issues

Hal Murray hmurray at megapathdsl.net
Tue May 15 15:27:56 EDT 2018

> Web sites such as "In The Sky.org" can generate useful plots for any
> specified location and time but I don't know if there's anything that will
> allow building a projected map over a period, and I don't suppose there's
> going to be anything anyway that allows experimatation with antenna angle
> etc, so that really leaves using lady H to generate the plots in real time,
> which she does do really well but for something like this might be akin to
> watching grass grow:-)

If you are far enough north, you are in the hole, but you can see the other 
side of the hole over the pole.

It's not hard to make your own plots.  This is from 66 38' north.

If anybody wants to play, I'll put the code on the web.

There are several steps.  First is to collect the data.  I have a python 
script that grabs everything from a NMEA device and logs each line with a 
time stamp.  The GPS orbit period is 12 hours so you need 12 hours of data to 
see everything.  But there are 30 satellites, so a few hours will show the 

The next step is to extract the data into a useful format.  That's another 
python script.  Then, just feed that to gunplot.

These are my opinions.  I hate spam.

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