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1.2.40 strange displayed S11 Smith value

 

Dave (W0LEV),

I climbed aircraft carrier masts in the 70's to tune antenna matching
boxes and told "bone-headed" acceptance engineers if they touched the
balancing biases in the radio room when the match circuit was within the
mfr specs that he'd have to explain to the ships captain why we could
not get underway. Yes, those circuits were very sensitive, but that was
why there is a +/- spec.

Mike C. Sand Mtn GA

On 1/26/2025 6:27 PM, W0LEV via groups.io wrote:
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 ¡À 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

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Virus-free.www.avg.com
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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.
 

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) ¦¸. I, for one, will not stand for any measurement with less accuracy.
 

This is why the true calibration aficionados only calibrate in the cold of outer space. There, the temperature is a nice, steady 2.72548¡À0.00057 K.

--
ww6x

On Sun, Jan 26, 2025, at 8:52 PM, KENT BRITAIN wrote:
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) ¦¸. I, for one, will not stand for any measurement with less accuracy.
 

Hi WW6X

as far as i know , there is some thin fim SMD 1% resistors that has less than 50ppm/¡ãC temperature coeff , so within 10¡ãC interval Room temperature +/- 5¡ãC the variation will be less then 0.05% which is very good and be measured and compensated, ( without touch it during long time with hand : hand temperature around 35¡ãC) .

i just realise this simple experience with my SEESII H4 and it's 50 ohm SMD calibration load (calibrated yesterday ) , it still giving a good result : 50.02 Ohm -j 0.001 Ohm after 24 hour calibration and 16¡ãC Room temperature and then I heat the 50 Ohm load by my hand to around 35¡ãC during more then 5 minutes and the result is still very good 50.03 Ohm -j 0.016 Ohm .
Sorry i can not change the atmospheric pression for more cheking .
This experience is very simple and can be done by any NanoVNA users .
Conlclusion : some 50 Ohm calibration load given by sheap NanoVNA's seems to be very good , in add it can be compensated with Dislord load conversion option to win some % or fraction of % more accuracy.

NB: I added some dielectric paste for all SMA Connectors including SMA load to avoid oxidation.

73's Nizar
 

On Mon, Jan 27, 2025 at 12:30 PM, Team-SIM SIM-Mode wrote:


NB: I added some dielectric paste for all SMA Connectors including SMA load to
avoid oxidation.
I suspect that it will instead catch grime and wear particles, especially in the crevices of the female sockets, making a nice grinding compound to cause unnecessary wear on your connectors.
Here is an oldie-but-goodie from HP:
Ignore the parts about APC-7 connectors, it is a OLD publication.
Instead of the recommended cotton swabs I use small, pointed foam swabs; high-quality standards have internal fingers in the female sockets which can be snagged and damaged by cotton fibers. No solvents besides isopropanol and Freon. Nothing harder than a wooden toothpick should be used.
For metrology work I wear cotton gloves to handle calibration standards, especially when handling Beatty standards which need to be kept scrupulously clean.
73, Don N2VGU
 

Only in some directions, average. The anisotropy of the Cosmic Microwave Background (CMB) is about 1 part in 1E5.

(and the temperature you radiate to in a blackbody sense only partly accounts for your temperature... given that most cal loads are shiny metal, I'd bet they get pretty hot out in space, if the sun shines on them - that epsilon/alpha ratio is important - as you burn your hand on the shiny seat belt buckle)

-----Original Message-----
From: <[email protected]>
Sent: Jan 27, 2025 8:10 AM
To: <[email protected]>
Subject: Re: [nanovna-users] 1.2.40 strange displayed S11 Smith value

This is why the true calibration aficionados only calibrate in the cold of outer space. There, the temperature is a nice, steady 2.72548&plusmn;0.00057 K.

--
ww6x

On Sun, Jan 26, 2025, at 8:52 PM, KENT BRITAIN wrote:
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.
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) &Omega;. I, for one, will not stand for any measurement with less accuracy.

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