Repeatability of stability measurements
I am trying to find out the limits of my measuring devices and
oscillators. Therefore I made 2 series of measurements with the same
conditions. In the first series I got 1 out of 10 and in the second 2
out of 10 results with much less noise. I looked at the results in
Timelab and then exported one good and one not so good result (recorded
4 minutes earlier) to stable32 for further analysis. Is this a problem
of my measurement setup or an artifact in the measurements. My
measurement device is a HP E1740A Time interval analyzer with about 50ps
(4.8828124999999998046875e-11) resolution. A Samsung STP2945LF (free
running) from my GPSDO as reference and the reference output of my
BG7TBL FA2 as measurement object. Attached are the results from the 2
series and the 2 further analyzed from the first series.
Hi Hans-Georg,
Does the E1740A also has the STP2945 as timing reference?
First of all, you have nice illustrations of the white phase modulation
noise slopes, of tau^1.5 as expected in the MDEV. Trouble is, it's not
pure WPM noise, but a mixture of the noise and the quantization effect.
So, it would be good if the E1740A is known to either free-float or
locked to one of the references.
By using MDEV you utilize the averaging benefits over the ADEV, giving a
sqrt(1E7) benefit as you hit 1 s. However, while your slope will roughly
coincide with the single-shot resolution, it's exact position is more
complex. The relative frequency may cause the resolution to go up and
down due to systematic nature, and the noise in addition to the signal
will intermodulate with the systematics.
If you have both these long-term locked to a stable source, it should
stabilize. Also, since you have a slow beating pattern of the
systematics, exactly when you measure may decide if it is high or low on
that valey.
You very clearly see systematic noise in the phase noise. These are for
sure fighing against you.
Do more of these phase noise analysis and see if any of the systematics
there coinside with high or low noise, or if indeed the noise floor
moves up and down.
This slope is more tricky than it get credit for.
Cheers,
Magnus
On 2022-06-23 22:56, Hans-Georg Lehnard via time-nuts wrote:
I am trying to find out the limits of my measuring devices and
oscillators. Therefore I made 2 series of measurements with the same
conditions. In the first series I got 1 out of 10 and in the second 2
out of 10 results with much less noise. I looked at the results in
Timelab and then exported one good and one not so good result (recorded
4 minutes earlier) to stable32 for further analysis. Is this a problem
of my measurement setup or an artifact in the measurements. My
measurement device is a HP E1740A Time interval analyzer with about 50ps
(4.8828124999999998046875e-11) resolution. A Samsung STP2945LF (free
running) from my GPSDO as reference and the reference output of my
BG7TBL FA2 as measurement object. Attached are the results from the 2
series and the 2 further analyzed from the first series.
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First of all the resolution factor from my first post is a copy error
the correct value is 4.8828124999999998-11 (less decimal places). In the
attached diagrams the correct factor was used.
I generated testfiles with 2046,2047,2048,2049,2050 intervals, loaded
into timelab and scaled them with 4.88281249999998-11.
MDEV shows more noise as real measurements . Another testfile with 2000
intervals and scaled with 5e-11 shows similar results.
In the Frequenc difference plot you can see the difference grows
stepwise with time. The zoom shows where the 2048 intervals are already
in the next time step and the 2000 intervals are not yet. By zooming in
you can also see this between the 2046 and 2050 intervals.
Possibly an overflow or rounding error ?
I think the overlap of this effect with the white noise of the real
measurements creates my measured jumps. More noise attenuates this
step-like progression.
Sorry, this was completely nonsense .. i correct the resolution factor
and forgot the "e" so i get 4.8828124999999998-11 as factor and scaled
the timelab plots with it. My interpretation is just as stupid.
The correct Factor is 4.8828124999999998e-11.
Am 2022-06-25 17:15, schrieb Hans-Georg Lehnard via time-nuts:
First of all the resolution factor from my first post is a copy error
the correct value is 4.8828124999999998-11 (less decimal places). In the
attached diagrams the correct factor was used.
I generated testfiles with 2046,2047,2048,2049,2050 intervals, loaded
into timelab and scaled them with 4.88281249999998-11.
MDEV shows more noise as real measurements . Another testfile with 2000
intervals and scaled with 5e-11 shows similar results.
In the Frequenc difference plot you can see the difference grows
stepwise with time. The zoom shows where the 2048 intervals are already
in the next time step and the 2000 intervals are not yet. By zooming in
you can also see this between the 2046 and 2050 intervals.
Possibly an overflow or rounding error ?
I think the overlap of this effect with the white noise of the real
measurements creates my measured jumps. More noise attenuates this
step-like progression.
time-nuts mailing list -- time-nuts@lists.febo.com
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Hi Hans-Georg,
You're MDEV slope is not that of white noise, but that of a (correlated)
systematic damping. You have 1/tau^2 rather than expected 1/tau^1.5.
Also, your levels are way off. This steeper slope for systematics is not
widely documented by the way, but direct consequence of the math.
This is where I slip between the wrapped-phase (w) and unwrapped-phase
(p) in TimeLab and figure out what is going wrong. That can be one hint.
Looking on your Frequency difference it may be that you have multiple
slips. Could it be that you loose data-samples and thus the phase-slope
jumps?
Here my main concern is the continuity of your data. That gives this
kind of severly distorted plot that swamps the real measurement quickly,
and is a sure give-away.
Cheers,
Magnus
On 2022-06-25 17:15, Hans-Georg Lehnard via time-nuts wrote:
First of all the resolution factor from my first post is a copy error
the correct value is 4.8828124999999998-11 (less decimal places). In the
attached diagrams the correct factor was used.
I generated testfiles with 2046,2047,2048,2049,2050 intervals, loaded
into timelab and scaled them with 4.88281249999998-11.
MDEV shows more noise as real measurements . Another testfile with 2000
intervals and scaled with 5e-11 shows similar results.
In the Frequenc difference plot you can see the difference grows
stepwise with time. The zoom shows where the 2048 intervals are already
in the next time step and the 2000 intervals are not yet. By zooming in
you can also see this between the 2046 and 2050 intervals.
Possibly an overflow or rounding error ?
I think the overlap of this effect with the white noise of the real
measurements creates my measured jumps. More noise attenuates this
step-like progression.
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
Hi Hans-Georg,
Maybe it is better to refer to this as the inverse of 20,48 GHz, since
that is the virtual clock rate of the interpolated coarse-clock.
Considering that it is 2048 * 10 MHz, it is not hard to imagine that a
coarse clock of say 80 MHz is then interpolated by 256 to achieve that,
which is entierly reasonable. 160 MHz and 128 is another example. A look
down the manual should indicate which one it is.
Cheers,
Magnus
On 2022-06-25 21:10, Hans-Georg Lehnard via time-nuts wrote:
Sorry, this was completely nonsense .. i correct the resolution factor
and forgot the "e" so i get 4.8828124999999998-11 as factor and scaled
the timelab plots with it. My interpretation is just as stupid.
The correct Factor is 4.8828124999999998e-11.
Am 2022-06-25 17:15, schrieb Hans-Georg Lehnard via time-nuts:
First of all the resolution factor from my first post is a copy error
the correct value is 4.8828124999999998-11 (less decimal places). In the
attached diagrams the correct factor was used.I generated testfiles with 2046,2047,2048,2049,2050 intervals, loaded
into timelab and scaled them with 4.88281249999998-11.MDEV shows more noise as real measurements . Another testfile with 2000
intervals and scaled with 5e-11 shows similar results.In the Frequenc difference plot you can see the difference grows
stepwise with time. The zoom shows where the 2048 intervals are already
in the next time step and the 2000 intervals are not yet. By zooming in
you can also see this between the 2046 and 2050 intervals.Possibly an overflow or rounding error ?
I think the overlap of this effect with the white noise of the real
measurements creates my measured jumps. More noise attenuates this
step-like progression.
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
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