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Hello everyone,

I have a nano VNA that is now refusing to read correctly after calibration it seems.
After running a one port calibration using the calibration assistant,
using the supplied open, short, and load calibration elements

... My normal technique is to do a scan of the Load element at the frequencies I have selected (before the calibration)... expecting to see a dot n the middle of the Smith chart and a straight 1:1 line on the SWR chart, as I believe the load element should be 50 Ω of pure resistance.

But as of yesterday that is not now how the device responds.
The Smith chart is covered in zigzags instead of even trying to be circles, and the SWR chart looks like a seismograph measuring a 5 on the Richter scale!

I've read on the topics here, and as a result, I have connected to the device on its COMport and done a "clear config 1234", followed by a power cycle and careful recalibration and retest against the Load, that got me nowhere. Same results on NanoVNASaver, and best I can tell on the tiny LCD, same thing....

what next, o guru's of the NanoVNA?

thanks and 73, Tim KA4LFP

Checking before calibration is not reliable.

Put it in the freezer for a few minutes and see if it works again until it warms up.

Gary AG7TH

On Sat, Jul 18, 2020 at 6:47 PM Tim Reimers KA4LFP <treimers95@...> wrote:

I have a nano VNA that is now refusing to read correctly after calibration it seems.
After running a one port calibration using the calibration assistant,
using the supplied open, short, and load calibration elements

... My normal technique is to do a scan of the Load element at the frequencies I have selected (before the calibration)... expecting to see a
dot n the middle of the Smith chart and a straight 1:1 line on the SWR chart, as I believe the load element should be 50 Ω of pure resistance.

But as of yesterday that is not now how the device responds.
The Smith chart is covered in zigzags instead of even trying to be circles, and the SWR chart looks like a seismograph measuring a 5 on the Richter scale!

Well, several things come to mind. First, did anything of note happen "yesterday" ? It is pretty easy to burn out the port if you accidentally transmit into it, or connect an "active" antenna which feeds back power into the VNA. Simpler question is are you using the correct port? The Nano VNA is not a two port device, it transmits only on one port (I don't really expect this to be the case but in the interest of completeness ...) Do you have a different load? If not do you have a 50 ohm resistor you can solder across a cable and plug that in and see what you see?

Things that might be helpful when using your VNA, a 6 dB pad to mitigate the effects of high SWR, and/or a DC blocker.

If you do the through port calibration does that work as expected?

--Chuck
AI6ZR

An easy to prove possible cause:

It could well be a contact (or less probably a PCB jack solder) problem.

Try to rescrew the plugs or gently rock them a bit.

The SMA cal Load received together with my NanoVNA caused that behavior, too. Purchasing another one fixed it.
If the cal Load is bad not at the contact, but inside, you may measure something different to 50 Ohms with a DC Ohm meter.
The cal Open cannot be the reason, as it is open anyway, but the cal Short might also have a contact problem.

73, Hans
DJ7BA

-----Ursprüngliche Nachricht-----
Von: [email protected] <[email protected]> Im Auftrag von Chuck
Gesendet: Sonntag, 19. Juli 2020 06:59
An: [email protected]
Betreff: Re: [nanovna-users] hi all...VNA noob here, encountering a problem I haven't seen before

On Sat, Jul 18, 2020 at 6:47 PM Tim Reimers KA4LFP <treimers95@...> wrote:

I have a nano VNA that is now refusing to read correctly after calibration it seems.
After running a one port calibration using the calibration assistant,
using the supplied open, short, and load calibration elements

... My normal technique is to do a scan of the Load element at the
frequencies I have selected (before the calibration)... expecting to see a dot n the middle of the Smith chart and a straight 1:1 line on the SWR chart, as I believe the load element should be 50 Ω of pure resistance.

But as of yesterday that is not now how the device responds.
The Smith chart is covered in zigzags instead of even trying to be circles, and the SWR chart looks like a seismograph measuring a 5 on the Richter scale!

Well, several things come to mind. First, did anything of note happen "yesterday" ? It is pretty easy to burn out the port if you accidentally transmit into it, or connect an "active" antenna which feeds back power into the VNA. Simpler question is are you using the correct port? The Nano VNA is not a two port device, it transmits only on one port (I don't really expect this to be the case but in the interest of completeness ...) Do you have a different load? If not do you have a 50 ohm resistor you can solder across a cable and plug that in and see what you see?

Things that might be helpful when using your VNA, a 6 dB pad to mitigate the effects of high SWR, and/or a DC blocker.

If you do the through port calibration does that work as expected?

--Chuck
AI6ZR




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Take a fine needle and gently bend the center connections on the SMA jack back together,