Hi
Well, what you are coming up with as a result simply is not correct. Properly
calculated ADEV does not do what you show it doing. TimeLab has been around
long enough to be considered “correct” in this regard. The normal input to an
ADEV calculation is phase rather than frequency.
Bob
>
I am starting with what should be a frequency measurement at the sample
rate. Timelab can import that and should be able to determine ADEV from
that. I agree that something is not right though. I unfortunately am trying
to measure with what I already have. I don't have a TIC.
Regards,
Mark
On
Hi
Let’s back up a bit:
The input to an ADEV calculation is a record of phase (time between wide spaced
edges). Often this is from a PPS output on a device. It could equally well be
from
10 MHz edges spaced a count of 10,000,000 edges apart.
The first part of the formula takes the difference
I have looked at it multiple times and so far cannot see a discrepancy. The
ration of the ADEVs for the two sample rates is very close to 2 for a wide
range of Tau in the 10-200 sec range. That can't be a coincidence. It's
between 2 and 3 for higher Tau but that may be due to temperature changes.
Hi
ADEV is pretty well documented and the results should *not* be dependent on the
sample rate. The proper approach to dropping the sample rate is decimation of
the
data. I think you may want to look at the way you are doing ADEV.
Bob
> On Dec 3, 2018, at 12:30 AM, Mark Goldberg wrote:
>
> I
I ran them again today and the results are almost identical. The slower
sample rate still shows a lower ADEV. I am not sure what the algorithm to
determine the peak frequency is but it is described as a linear
interpolation between the two highest peaks on the FFT. I could see how
that could be
Hi
Looking at the data, I’m guessing the slower sample rate was done last. If so,
you may not be letting the GPSDO’s “warm up” long enough. Most designs
take days (if not weeks) to get to their ultimate stability.
Bob
> On Dec 2, 2018, at 11:16 AM, Mark Goldberg wrote:
>
> I broke down and
Not all the "holdovers" on the Trueposition are due to signal issues. Many
seem to be related to it tuning itself up after a power cycle and they improve
or go away after a couple of days of running.
But your antenna signal level map is rather awful... lots of red. It could be
antenna,
On Fri, Nov 30, 2018 at 8:56 AM Attila Kinali wrote:
> On Thu, 29 Nov 2018 21:22:44 -0700
> Mark Goldberg wrote:
>
> > How much could I expect ADEV to improve if I move the antenna to a better
> > location with clear view of the sky? The things I am testing need to be
> > better than 8e-10, so
Hi
There are lots more issues to GPSDO stability than just antenna placement.
Indeed
you are correct that a location that keeps you out of holdover is a must.
Ideally you
want to be able to lock on to 4 sats at all times. That generally equates to
being able
to “see” something in the > 6 range
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