[time-nuts] Help with Novatel OEM6 external oscillator

[Skip Withrow]

Hello Time-Nuts,
Hopefully, this doesn't get too long.  What I desire to do is hook up
an external oscillator to a Novatel OEM6 series dual-band GPS
receiver.

Sounds easy. But, Novatel has four fixed (TCXO, OCXO, rubidium,
cesium) plus a USER specifications to model the external clock
performance.  Each model specifies three coefficients of the power law
spectral density (h-2, h-1, h0).  If you google 'novatel
externalclock' you can see the command. My question is, how do I
translate an oscillator ADEV plot into the three coefficients?

I'm not an oscillator noise guru by any means (in fact, I'm probably a
noise dummy).  It took me a while to figure out that the number range
that Novatel is looking for is Allen Variance.  So taking the square
root of their model numbers would be Allen Deviation (hope this is
correct).  I believe the h-2 coefficient represents Random Walk FM
(Would this be slope=-2 on ADEV plot?), the h-1 would be Flicker FM
(slope =-1?), and the h0 coefficient would be White FM (slope =1 (or
is it 0)?).

If I look at oscillator ADEV plots I often don't see anything as steep
as -2 slope.  Is this because it is below the lowest tau of the plot
and/or below the noise floor of the measurement system?

The real question is how to I translate a typical ADEV plot into the
three coefficients that the Novatel receiver wants to see.  An
illustrative example would be most helpful.  From looking at the
numbers in the Novatel documentation it appears that the h-2 number
represents short taus, h-1 intermediate taus, and h0 long taus.

For extra credit - Google ' Novatel clockmodel', and explain (simply)
what the covariance matrix is.  Again, if an illustrative example
could be shown it would be most helpful.

That's all for now before my brain explodes.  Thanks in advance for any help.

Regards,
Skip Withrow