[time-nuts] Tbolt issues
EWKehren at aol.com
EWKehren at aol.com
Fri Sep 2 09:13:41 EDT 2016
Charles,
would you please share your settings, this is exactly what we are looking
for. We are doing it by trial and error but your expertise will help
greatly.
English not being my native language linguistics are some time a problem
Thanks
Bert
In a message dated 9/1/2016 6:26:32 P.M. Eastern Daylight Time,
csteinmetz at yandex.com writes:
Bert wrote:
> maybe some one smarter than us can working with the parameters that Tbolt
> makes available better performance can be achieved
I am quite sure of that
> the frequency is being changed to compensate for time
Yes, the PPS is steered by making slight adjustments to the OCXO
frequency. But you can make these adjustments as arbitrarily small as
you want with the setup parameters. I run my Tbolts with pretty tight
limits on the frequency adjustments.
> and we do not care about ADEV, we care about the actual
> frequency at that moment it goes in to the measuring device
There is no "there" there. One never makes a frequency measurement at
just one instant -- the measurement will ALWAYS be done over a macro
time interval (very often, one second, sometimes 0.1, 10, 100, or 1000
seconds). We never observe, and have no way to know, the instantaneous
frequency (as you put it, "the actual frequency at that moment it goes
into the measuring device") -- so how can we care about it? The only
thing relevant (or even meaningful) is the average frequency during our
measurement interval.
xDEV tells us half of what we want to know -- how stable our oscillator
is from one measurement interval to another. We would also like to know
what frequency it is wobbling around -- the "centroid" frequency, if you
will (to borrow a geometric term). (Mathematicians can argue for days
about which type of "average" is appropriate here -- the rest of us just
pick one and carry on.) ADEV does not tell us this "centroid" frequency
directly, but it can be extracted from the same measurements we took to
calculate ADEV.
I think you are being misled by a belief that the linguistic construct,
"instantaneous frequency," has real meaning in the world. It doesn't.
Best regards,
Charles
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