John Miles wrote:
This is my first Allan Deviation plot. It consists of the PPS
output of an Oncore GT+ (Navigation-grade) GPS vs. an Ovenaire
10MHz OCXO divided down to 1Hz via an HP 5328A counter. The HP
5370A is free running on its 10811-60101 OCXO. The
control/plotting is done by KE5FX's T.I. utility software.
The curve clearly shows the limitations of the GPS at Tau=1s...
But what else can be said of the GPS, or of the test setup when
looking at the plots?
It sounds like there might be a scaling problem. Do you have the 1-Hz input
connected to START and the 10-MHz output from the GPS connected to STOP?
That's really the best way to go, unless the DUT is drifting so much that it
covers the whole 100-ns period range in only a couple of measurement cycles.
That won't work as one of the sources is the PPS output from an Oncore
GT which has a PPS error spec < 500ns with SA on.
Whilst it may be a little lower without SA, it may be still be somewhat
greater than 100ns.
Dividing the 10MHz down to 1MHz or perhaps 100kHz would be better.
The 5370A timebase noise contribution to the measurement error will
still be insignificant.
The plot doesnt appear too discordant with the Oncore GT spec.
Bruce
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