Re: Cal-Kit Standards' Definitions


Dr. David Kirkby from Kirkby Microwave Ltd <drkirkby@...>
 

On Sun, 29 Sep 2019 at 12:16, Kurt Poulsen <kurt@hamcom.dk> wrote:

Hi Jeff
However the NanoVNA has already a build in correction for the open in the
form of 50fF which is pretty much correct for the CH0 Female SMA left open,
so to use the supplied open standard is wrong and is adding further delay.

That is acceptable if your DUT has a male SMA connector, but it is not if
you wish to use any other sort of connector.


Basicly the NanoVNA is for me the "engine" and for using other calibration
kits the way is to use the NanoVNA-saver

That is your intended use Kurt, but it is certainly not how I intend using
the NanoVNA. For my use, which is to use it as an entirely self-contained
unit, being able to define calibration kits in the NanoVNA is important,
whereas using the NanoVNA with external software is less so.

where you can enter delays and L and C coefficient IF YOU HAVE THEM and
that is not the case for the majority of NanoVNA users for whatever
homemade kit they want to use.

You can estimate that based on physical measurements as you well know.

One must remember to subtract the 50fF from the Open as the NanoVNA is
internally pre-compensated by 50fF equal to a one way delay of 2.5ps.

Or better still remove that 50 fF, and let the user define calibration
kits. Let the NanoVNA default to using the calibration kit supplied, but
allow the user to enter a kit(s) with defined parameters.

David is giving a comment the a short always has a longer delay than open,
and that can be misunderstood. That is not the caser for the supplied kit
for the NanoVNA.

I was talking about the vast majority of professional calibration kits.
Clearly Jeff is thinking about the higher quality kits. When I mentioned
that supporting C1, C2, C3, L0, L1, L2 & L3 would be better for homemade
kits, he pointed out that was not his main aim.


I have made a comment on this on this reflector as it is anticipated to be
0ps by design but it has a very small negative value. I did measure the
supplied kit based on calibration by my HP 3.5mm kit on another VNA and I
will repeat and publish the result for those values to be entered in
NanoVNA saver. It would be nice if David had done that instead of lecturing
about the way he seem everything.

Initially people were saying that the NanoVNA assumed ideal standards. Now
I believe it’s a 50 fF open and probably an ideal short. As you say, the
short supplied has a small negative delay.


Long live a pragmatic approach


The correct pragmatic approach depends very much on ones intended use,
which will be either

* *Use the NanoVNA standalone*, requiring support for calibration kits
internally *in* *firmware*. Jeff has convinced me that a delay for the
opens and shorts, as well as C0, is adequate for the HP calibration kits. I
don’t think that’s the case for homemade kits though.

* *Use the NanoVNA as data collection device*, and perform other functions
with external software.

That’s two very different uses, requiring a totally different approach


Kind regard

Kurt

Dave
--
Dr. David Kirkby,
Kirkby Microwave Ltd,
drkirkby@kirkbymicrowave.co.uk
https://www.kirkbymicrowave.co.uk/
Telephone 01621-680100./ +44 1621 680100

Registered in England & Wales, company number 08914892.
Registered office:
Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3 6DT, United
Kingdom

Join nanovna-users@groups.io to automatically receive all group messages.