Hi

Sweep the transfer function from 100 Hz down to 0.001 Hz at 50 points per decade.
Spend enough time at each point to get to 0.001 db sort of accuracy. The first decade
goes pretty fast. That last decade ( 0.01 Hz period to 0.001 Hz) …. not so much. The
request always has both the silly frequency and the nonsense db fraction in it ….

Bob

On Thu, 30 Nov 2017 09:39:59 -0500
Bob kb8tq kb8tq@n1k.org wrote:

What puzzles me here is, the reason why someone would care
about sub-1Hz frequencies in a telephone system? IIRC POTS
did cut off somewhere areound 100-300Hz anyways.

		Attila Kinali

--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson

Hi

They aren’t looking at voice signals, they are looking at the distribution
of timing signals. The filters cut off well below voice frequencies. The
issue (as originally mentioned) is peaking in very long chains of repeaters.
Since the cutoff can be very low (just like with a GPSDO), the frequencies
involved in a full amplitude and phase sweep are very low as well. If you want
very tight db accuracy, that pretty much implies that you have a good number
for “zero” frequency …… that puts you into silly season if somebody decides
it must be “tested in”.

Bob

In message 20171130181024.832c6adfd3cea0658ba430f1@kinali.ch, Attila Kinali w
rites:

They did not.

Most carrier frequency facilities had bottom frequencies in the 50kHz
area or higher.

Bob brought up the sub-Hz stuff, I pressume he knows what it is used for.

--
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.

Poul-Henning, Magnus, et al. thanks for your suggestions - they were not in vain.

As promised, I started setting up dual asynchronous sources experiment and performed a quick sanity check.
What I have [unsurprisingly] found is that at this level controlled environment is a problem in itself.
For example, undoing input signal SMA connector by one turn shifted my results by around 3.5ps - close to expected figure but still inconvenient.
I'll have to plan the setup before I build and validate it, otherwise the results are not trustworthy.

I hope this message makes it to the list - my previous one didn't.  I am staying off the list for now.

Thanks
Leo

P.S. I do know about torque wrenches.

On 29 Nov 2017, at 21:51, Poul-Henning Kamp wrote:

On Fri, 1 Dec 2017 21:10:55 +0000
Leo Bodnar leo@leobodnar.com wrote:

3.5ps is pretty much what I'd expect in additional delay, when undoing an
SMA connector by one turn. One turn is about 0.7mm, assuming a VF of 0.6
you get to ~3.5ps.
I am quite impressed that you could measure it this accurately.
What measurement technique do you use?

			Attila Kinali

--
<JaberWorky> The bad part of Zurich is where the degenerates
throw DARK chocolate at you.

Hi,

On 12/02/2017 11:05 AM, Attila Kinali wrote:

There is a reason that one should use SMA momentum keys for repeatability.

A VNA should not have a problem measuring that at RF frequencies.

Cheers,
Magnus