[time-nuts] A question about anomolous Alan Deviation Measurements.

[morrie at iometric.com]

I am using a Fluke PM6690 counter measure the Alan Deviation
of various pairs of 10 MHz OCXO's in use in my lab.

I discovered that I can measure a (tau = 1 sec) low value of say 6.0E-12
on a good set, but only If the crystals are tweaked so the delta is some
0.5 ppm.  If they crystals are tweaked to be within a mH, then the Alan
Deviation zooms to about 5 times higher.

I suspect a flaw in my PM5590 unit or in its design, and I guess will
hunt around for something better.

Does anyone have experience with this phenomena?  Does one always
have  to separate the clocks being compared to avoid this "beating"?

Thanks,
Morrie Altmejd