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On Jan 27, 2025, at 07:47, Fred_M via groups.io
<dl4zao@...> wrote:

? Sad news:


(mostly electronics) is no longer available.

regards
Fred





<Owen Duffy Article.pdf>

Uhhhh ..... that level of accuracy is only true at one Altitude,
Temperature, and Relative Humidity!


As they say, "Why be approximately correct when you can be precisely wrong?"

On Sunday, January 26, 2025 at 10:01:39 PM CST, Mike C.
<mg@...> wrote:

Don't buy a VNA of any sort, sounds good to me, what do you think. This
is accurate to .0000000000001%, close enough??

Mike C. Sand Mtn GA

On 1/26/2025 12:15 PM, ww6x via groups.io wrote:

The impedance of free space is Z? = 376.730313412(59) Ω. I, for one, will not stand for any measurement with less accuracy.

On Jan 27, 2025, at 1:07?AM, Fred_M via groups.io <dl4zao@...> wrote:

?On Mon, Sep 30, 2024 at 10:31 PM, AG6CX wrote:

Google Owen Duffy Mostly Electronics

Owen Duffys blog owenduffy.net seems to be offline.
Message: "content no longer available"

it would be a great loss if his site remained closed.

regards

The impedance of free space is Z? = 376.730313412(59) Ω. I, for one, will not stand for any measurement with less accuracy.

Thanks, Jim Lux! This is why I routinely remind others on the groups to
which I subscribe and contribute that we, professionals, amateur radio
operators, non-professionals, service technicians, or even (heaven forbid,
CB'ers) are not running a metrology lab. Unfortunately, some take offense
at that. But it's so true.

My last job working for Uncle at Phillips Lab in Albuquerque addressing
HPPM, we cal'ed in the evening ready for the next morning runs of the
"machines" . Then the instructions/orders were given that NOBODY moves
ANYTHING or even breathes on the equipment and cabling. No janitors or
cleaning permitted. We were expected to offer repeatability in our
measurements within ± 0.5 dB. Believe me, that's a license for a major
headache the next morning if there was a power outage overnight.

Dave - W?LEV

<>
Virus-free.www.avg.com
<>
<#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>

On Sun, Jan 26, 2025 at 8:48?PM Jim Lux via groups.io <jimlux=
[email protected]> wrote:

Measuring resistance to 4 or 5 digits is challenging with good
repeatability. What’s the temperature coefficient of your unknown? What’s
the tempco of your measurement system.

And of course, the DC resistance is related to, but not necessarily equal
to, the RF impedance at other frequencies. That’s where the art of
precision terminations is.

BTW, the specifications on things like terminations is more about the
practical uncertainty of the manufacturing test set up. That’s why you see
connectors specified as VSWR<1.03. In reality, they’re all a lot lower,
but it’s a pain to measure in a manufacturing environment.

I suspect that other things in your VNA system would be larger
contributors to uncertainty.
Mate/Demate is one of them. NanoVNAs don’t come with precision connectors
like APC-7. And cable flex is another. Those $5000 cables for VNAs are
partly because they’re reasonably phase stable with some amount of flex;
and people still tape them down to the bench when making measurements on
multiple UUTs.

There is a whole literature and annual conferences on precision RF
measurements. People devote their entire life to eking out the next digit.

On Jan 26, 2025, at 12:32, Team-SIM SIM-Mode via groups.io <sim31_team=

[email protected]> wrote:

?Hi WW6X

HP 909 coax terminaison seems to be garanteed to 50 +/- 0.2 Ohm from

DC to 2Ghz , and it costs more than twice NanoVNA's .

For HF band it should have better accuracy .
Some resistor meters can have at least 4 significant digits accuracy

which allow to compensate error by reference load function included on
DiSlord FW 1.2.40 example : 50-->50.3 Ohm around 0.6% correction

73's Nizar.

The impedance of free space is Z? = 376.730313412(59) Ω. I, for one, will not stand for any measurement with less accuracy.

On Jan 26, 2025, at 12:51, Dave Daniel via groups.io
<kc0wjn@...> wrote:

? Jim,

Do you refer to John Taylor's "An Introduction to Error of Analysis"?
That's the text that I used in college, and the photo on the cover is so
great that I have a framed poster of it on a wall in my lab.

DaveD
KC0WJN


On Sun, Jan 26, 2025 at 15:40 Jim Lux via groups.io <jimlux=
[email protected]> wrote:

Probably not 12. :)

But really, let’s look at it.

Reflection coefficient is what? <0.005 or <0.0025?

Rho= (Z1-Z2)/(Z1+Z2)

So we’re looking at about 3 or 4 digits, which is pretty good.

The challenge would actually be the uncertainty in the connector mate.

About 25 years ago I was developing a noise source for calibrating a

precision receiver at 13.402 GHz. ?We wanted to measure the transmitted

power from the QuikSCAT satellite at a ground station to tenths, if not

hundredths of a dB, so the whole system was an exercise in driving

uncertainties down everywhere in the system.

We sent it off to NIST to test on their fancy calibration system (They

published a paper about it, along with some other sources). ?As I recall,

the mate/remate uncertainty (for lapped and pinned wr-62 waveguide) was

given as a few Kelvins out of 7000K for the source, and can fairly be

called state of the art. ?That’s about 4 digits, maybe 3.5. That’s power,

not voltage.

I’d say that anyone claiming a measurement uncertainty for an absolute RF

power measurement (which is what VNAs basically do) of better than 1E-4

(linear) is probably stretching. One can do more accurate relative

measurements, of course, particularly if the system doesn’t change (no

mate/demate).

So

A) the fact that we know some physical constants (Z0 of free space, speed

of light) to a lot of digits is a testament to some experimentalists

ingenuity and attention to details.

B) lots of digits is not worth worrying about in day to day, or even

unusual, applications.

C) Understanding uncertainty is important, even if you don’t do it in a

formalized way. ?(There is a whole book and standard on this, of course).

Just for folks contemplating pushing the limits - don’t forget things like

solid earth tides and relativistic corrections. (See project GREAT as a

demonstration of general relativity). ?In reality, just dealing with the

temperature cycling from the HVAC in your lab will be the dominant source

for a lot of things.

And pushing the limits on uncertainty can be fun.

On Jan 26, 2025, at 12:01, ww6x via groups.io <ww6x=

[email protected]> wrote:

?If one were to buy an HP 909C with ISO IEC 17025 Accredited

certification (about $400 total), how many guaranteed decimal places would

that have?

--

ww6x

On Sun, Jan 26, 2025, at 10:41 AM, Jim Lux via groups.io wrote:

Indeed. ?Well, that’s, what, 1 part in 1E12?

There are relatively few things one can measure to that kind of

precision. ?In the Radio Science world, they measure the round trip

delay of a radio signal to Jupiter and back to a bit better than that.

One can build/buy a device that gets 1E-12 Allan deviation for time

over, say, 1000 seconds. ?See the time-nuts mailing list.

Voltage (and current) are a bit tougher, if only because finding a

standard to calibrate against is hard. ?24 bit ADCs and DACs are fairly

common, and achieve relative accuracies of maybe 2^22. That’s a 1E-7

kind of uncertainty. But finding absolute voltage references is tough -

there are semiconductor band-gap references that are maybe 1ppm (1E-6).

Doing better as a primary standard would be a Josephson junction which

turns voltage into frequency, which can be measured quite accurately,

but the need for 4K temperatures makes that challenging. (See Volt-Nuts

mailing list - there could be tricks to get better)

On Jan 26, 2025, at 09:15, ww6x via groups.io <ww6x=

[email protected]> wrote:

?The impedance of free space is Z? = 376.730313412(59) Ω. I, for one,

will not stand for any measurement with less accuracy.

--

ww6x

On Sun, Jan 26, 2025, at 9:00 AM, Jerry Stuckle wrote:

It is close enough for YOU. ?It is NOT close enough for everyone.