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Some readers of my Tips for New Users document pointed out that there was some ambiguity about the type of SMA adapter that should be installed onto the calibration standards. It depends upon whether or not you intend to use coax jumpers to connect the DUT to the VNA. If you use jumpers, the adapters should be female SMA to female SMA. If you like to attach the DUT directly to the VNA, then the adapters for the calibration standards should be female SMA to male SMA.

I have attempted to clear up the issue, and have included some pictures to illustrate the options. The suitably modified document is attached.

If you see other problems, please let me know.

In addition, some folks pointed out that this had drifted away from the original topic. So it now has its own topic. :-)

Thanks,
Mike WY6K

On Wed, 2 Oct 2019 at 04:52, mike watts via Groups.Io <wy6k=
[email protected]> wrote:

Some readers of my Tips for New Users document pointed out that there was
some ambiguity about the type of SMA adapter that should be installed onto
the calibration standards. It depends upon whether or not you intend to
use coax jumpers to connect the DUT to the VNA. If you use jumpers, the
adapters should be female SMA to female SMA. If you like to attach the DUT
directly to the VNA, then the adapters for the calibration standards should
be female SMA to male SMA.

I have attempted to clear up the issue, and have included some pictures to
illustrate the options.

Thanks,
Mike WY6K

If you add a female-female adapter onto the supplied short you will really
mess up its properties. The short supplied has a *very* small negative
delay. As far as I am aware, that’s not accounted for in the firmware, but
it really is so small to be of little practical significance. If you then
and a female-female adapter onto the short standard, it will introduce a
one-way delay of about 42 os, or two-way delay of around 84 ps. (The exact
amount depends on the adapter.) That will add a significant error, which
can not currently be compensated for in the firmware.

Additionally, you will get more stable results if you don’t use cables. ALL
cables will introduce some amplitude and phase instability as they are
flexed or their temperature changes.

I would suggest that you advise people to put m-f adapters on the NanoVNA.
The delay of such adapters will be a but longer, but the calibration should
remove that.

I really can’t see how your advice is good.

Dave.

--

Dr. David Kirkby,
Kirkby Microwave Ltd,
drkirkby@...

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

Keeping things in perspective it looks to me that we might be getting confused expecting to use a $50
hobby device with hobby grade calibration standards when a $5000+ instrument and professional cal
standards would be more appropriate for the delay figures being mentioned to be of any relevance.

Not withstanding the above the NanoVNA is an extremly effective tool and the suggested use of
m/f SMA adapters to reduce wear on the board mounted connectors is good engineering practice.


73 Bob GM4CID

On Wed, 2 Oct 2019 at 10:09, GM4CID <gm4cid@...> wrote:

Keeping things in perspective it looks to me that we might be getting
confused expecting to use a $50
hobby device with hobby grade calibration standards when a $5000+
instrument and professional cal
standards would be more appropriate for the delay figures being mentioned
to be of any relevance.

I would disagree.

SDR-KITS sell a reasonable SMA female calibration kit for ?67.20



I actually thought they did an even cheaper one, but I can not find it.

Rune has added support for calibration kits in his software.

All of the above will work reasonably well if people add connectors savers
(m-f) on the NanoVNA.

Anyway, let’s agree to differ. ?????

73 Bob GM4CID

Dave G8WRB
--
Dr. David Kirkby,
Kirkby Microwave Ltd,
drkirkby@...

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

The suitably modified document is attached.

Updated Wiki link: /g/nanovna-users/wiki/User-Guides

David, despite agreeing to differ, might I suggest that it would be useful if
someone like yourself with the appropriate calibrated professional equipment
could offer to measure the three cal standards supplied with the nanoVNA
and publicise the results and conclusions
I do appreciate that in an ideal world testing of an appropriate sample size
would be more meaningful.

Regards Bob

Hi Bob
I have done it, as I earlier promissed and will as soon I get the report finalized and the characterization tested against the NanoVNA-Saver
Kind regards
Kurt

-----Oprindelig meddelelse-----
Fra: [email protected] <[email protected]> P? vegne af GM4CID
Sendt: 2. oktober 2019 14:22
Til: [email protected]
Emne: Re: [nanovna-users] Quick Tips for New Users

David, despite agreeing to differ, might I suggest that it would be useful if someone like yourself with the appropriate calibrated professional equipment could offer to measure the three cal standards supplied with the nanoVNA and make public the results and conclusions I do appreciate that in an ideal world testing of an appropriate sample size would be more meaningful.

Regards Bob

On Wed, 2 Oct 2019 at 13:22, GM4CID <gm4cid@...> wrote:

[Edited Message Follows]

David, despite agreeing to differ, might I suggest that it would be useful
if
someone like yourself with the appropriate calibrated professional
equipment
could offer to measure the three cal standards supplied with the nanoVNA
and make publicise the results and conclusions
I do appreciate that in an ideal world testing of an appropriate sample
size
would be more meaningful.

Regards Bob

I did post the results of the open earlier. Kurt is going to do more, but
my executive summary is that the cal kit supplied to me is quite
reasonable. Far from perfect, but quite reasonable. The fact that the
connectors rotate the contact surfaces is not great, but not a
deal breaker.

Problems will lie with SMA female calibration standards, as well as all N
bits except female N shorts.

APC7, which is very rare would again work reasonably well. The fringe
capacitance of APC7 is a bit higher than the 50 fF assumed in the NanoVNA
firmware, but would be reasonable.

You can cobble together your own standards using little more than a few
connectors and a ruler. I am sure Kurt can give you some advice.

The problem is currently the NanoVNA has no support *in firmware* for any
sort of calibration kit, so whether you make something, or buy an expensive
kit, you are going to be in the same position.

Rune’s program does now I believe add support for calibration kits, but
that’s no help if you want to use the NanoVNA outside a laboratory without
some sort of PC, laptop or tablet.

Dave


--
Dr. David Kirkby,
Kirkby Microwave Ltd,
drkirkby@...

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

Hi Kurt,

Thank you, I look forward to your report.

With regards,

Bob