[time-nuts] GPS receiver testing

[Tom Van Baak]

Measuring 1PPS stability requires a counter and a reference. As Said mentioned, the counter requirement is fairly simple: any sub-nanosecond counter like a 53132A is fine (higher resolution is wasted anyway). But the reference requirement is the more difficult. If you want to measure down to nanoseconds a day, you need either a good cesium or an H-maser. That's why most people send their GPSDO to a timing lab for these measurements.

If you use a GPSDO as a reference you find yourself in the awkward position of using one GPS product to measure another GPS product. I suspect this would create more questions than answers. Alternatively if you use a GPS simulator you can cancel out the instability of the reference. In theory.

If you're just trying to measure down to the 10 ns or 100 ns level, then any old Rb or Cs reference will do.

John is also interested in measuring *accuracy*. This is really hard since it involves bringing equipment to NIST or USNO or similar timing installation and/or using antenna test chambers, etc.

Please read John Plumb's paper:
http://tycho.usno.navy.mil/ptti/ptti2002/paper29.pdf

and Rick Hambly's paper:
http://tycho.usno.navy.mil/ptti/ptti2002/paper9.pdf

For further information, google for: gps "absolute calibration"
and you'll find many papers. All the UTC(k) need to do this for their submissions to BIPM so there is no shortage of information on this topic.

/tvb