ok Bob,

Then how do you tease out the difference between the clean generated 60Hz
and the mains 60Hz adev curves to determine what is noise and what is the
variability in the 60Hz?  That is the point of my question not semantics
about ideal vs non-ideal.

doc

On Mon, Nov 18, 2013 at 8:36 PM, Bob Camp lists@rtty.us wrote:

--
Doc

Bill Dailey
KXØO

Hi Bob,

The goal of the red trace was to see if a fancy hp 33120A would give better or worse or same performance as mains 60 Hz. This simple substitution technique is a quick way to check if mains or the picPET might be the limiting factor. The slope and intercept suggests the picPET has resolution of at least 1e-6/tau. I say "at least" because we don't know how much of that is due to the 33120A.

Notice that for tau greater than about 1/3 second, picPET (and REF) instability is significantly below mains (DUT) instability. For tau 0.01 to 0.3 s it would take more work to quantify which pieces are contributing to the instability pie.

Attached is an ADEV plot; this one includes the past two weeks, and also a 100 day continuous run from Feb/Mar/Apr/May 2012. The GPSDO-like steering of mains frequency is visible in this trace.

You also might be wondering why the red trace hits a floor and drifts up. That's due to the TCXO in the 33120A. The reference for the picPET was one of those cute 10 MHz Micro-Crystal DIP OCXO, which easily outperforms the TCXO.

/tvb

In message 77A742979E2849FD9CA585192F2F5AFC@pc52, "Tom Van Baak" writes:

It doesn't really make sense to talk about taus less than approx
0.1s for Mains.

It is not atypical to see 10% "harmonic distortion" on mains in a
household, most of it from switchmodes, but also single-phase
motors etc.  Music amplifiers, in particular played at "teenagerockgod"
volumes add a very interesting challenge too.

In theory harmonic distortion does not change your zero-crossings,
but it is not really "harmonic" in the Fourier sense, it's just
mostly centered around the overtones.

Either you include the "harmonic" distortion, and then your measurement
applies only to that specific outlet, when the dish-washer is running
exactly 20 minutes into programme 3 and no kids listen to loud
music.

Alternatively you can put mains through a 40-60 or 50-70 Hz
bandpassfilter to supress anything but the the fundamental, but
what exactly do you measure then ?

Once you get below about 1Hz, the most interesting thing you can
do with mains is to sample it at ~4kHz, make a water-fall plot and
try to identify your house-hold appliances by their distortion
patterns :-)

--
Poul-Henning Kamp      | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG        | TCP/IP since RFC 956
FreeBSD committer      | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

Hi

I spent a lot of time with a sine wave input on this sort of stuff… You can come up with a line that the floor must be below. Find a better source and that line moves down. You can’t find the actual floor. You can only establish that it must be below this or that level. It’s not like the noise floor of a radio….

Bob

On Nov 19, 2013, at 6:06 AM, Tom Van Baak tvb@LeapSecond.com wrote:

HI

There is no way to tell that the “clean” 60 Hz is actually clean. It’s got a noise component in it. The noise actually is surprisingly high. The picPET is actually a bit better than that plot would suggest.  You can say that the noise of the picPET is below the “clean” line and move on, but that’s not the whole story.

Bob

On Nov 18, 2013, at 10:54 PM, Bill Dailey docdailey@gmail.com wrote:

Em 19/11/2013 09:31, Poul-Henning Kamp escreveu:

The odd ones doesn´t, but the even ones do... and they happen.

Daniel

"Alternatively you can put mains through a 40-60 or 50-70 Hz
bandpass filter to suppress anything but the fundamental"

The problem with any filtering is precisely that the phase shift through any filter is highly dependent on the actual signal frequency, so if your purpose is timing, the filter will probably do more damage than help. Tom's data shows that "no filter" works well at his location, which is probably typical, aside from the large number of precision time references in the basement :)

I have some data about filtering the mains I am trying to put together in a web page. Will take a few days. That data was collected with regard to power factor correction, not timing, but it is within the scope of what has been discussed in this thread and it may be interesting to the curious mind.

Didier KO4BB

Poul-Henning Kamp phk@phk.freebsd.dk wrote:

--
Sent from my Motorola Droid Razr 4G LTE wireless tracker while I do other things.

Filter families that aim for super flat passbands and super steep skirts
have the craziest phase response. They also "ring like a bell" when hit
with impulses.

Other filter families aim for well controlled phase response but give up
flat passbands and super steep skirts. They do not "ring like a bell" when
hit with impulses.

Gaussian filters work very well for well controlled phase response and are
used in e.g. oscilliscopes and other applications where the data is eyed
critically in the time domain.

In communications and time-domain work, it is common to use a filter that
has well controlled phase delay across the passband, but still has somewhat
steep skirts and can have less well controlled phase delay outside the
passband. In the literature these are called "Gaussian to 12dB" and
similar. They are a joy to listen with, in environments with impulse noise,
compared to the typical steep-skirt filters.

Tim N3QE

Tim.

On Tue, Nov 19, 2013 at 10:06 AM, Didier Juges shalimr9@gmail.com wrote:

Tom,

On 18/11/13 23:15, Tom Van Baak wrote:

I don't have much of that myself. I do recommend you to check the
presentations of the NASPI conference (naspi.org). There is plenty of
plots there.

Well, I should toss that over to the good folk at NIST doing
synchrophasor calibrations. Should I grab them now that we are in the
same room?

Have a look at IEEE C37.118.1 for measurement methods.

Well, if you are happy with that, fine. But there are many things
happening on the grid which needs deep analysis and the tools for it has
been developed to provide both resolution and removal of noise which is
not part of the measurments. Just calibrating the trigger noise for a
PMU requires care, as the S/N required for a straight comparator for the
applications is several tens of dBs away from a good conditions, so they
have had issues with doing that.

Doing your own time-stamping like you have done is naturally fun, but do
not confuse it with the experience and processing that have been shown
needed by an industry.

BTW. WECC, who has a large network of PMUs, and that covers where you
have your house and measurement point, can't release detailed data to me
or you just for fun. It always needs to be cleared from a security point
of view.

Cheers,
Magnus

So we know there are deviations in line freq. But it seems strange in this era of very accurate and inexpensive freq references.
How much is related to the generation? It seems in this era of switching supplies and other complex loads that even if the power were perfect at the generator the phase/freq could vary widely across the grid as different parts of the sine wave are loaded in a non linear fashion. And could a small digital signal be added to the smart grid that would control switching supplies to correct rather then degrade the grid signal?

Thomas Knox