Hello,

I recently received my NanoVNA V2 Plus4.
I updated the firmware to the latest *20220301* version.
I connected one blue cable to port1 and performed a T/R calibration using the included standards. For the Thru I connected the cable straight to port2.
Then I connected the other blue cable to check its response.
There are significant ripples on S21 plot. I have already measured the blue cables in a vna at work and they are good, straight lines.
Why is the ripple there? Is my unit malfunctioned?
Please find screenshot attached.

Thanks
John

Additional information:
Device purchased from Tindie and delivered a few days ago.
S11 measurements are very good using the *20220301* firmware.

S21 are not good at all and not usable.
Please let me know if this is due to the device or the firmware, and if there is a way to fix it.

John,
What does S11 look like when you use the other cable?
I suspect you are seeing a combination of mismatch at port 2 and two blue cables with unequal Z0.
--John Gord

On Tue, May 10, 2022 at 10:15 PM, <gouzou82@hotmail.com> wrote:

>
> Hello,
>
> I recently received my NanoVNA V2 Plus4.
> I updated the firmware to the latest *20220301* version.
> I connected one blue cable to port1 and performed a T/R calibration using
> the included standards. For the Thru I connected the cable straight to
> port2.
> Then I connected the other blue cable to check its response.
> There are significant ripples on S21 plot. I have already measured the
> blue cables in a vna at work and they are good, straight lines.
> Why is the ripple there? Is my unit malfunctioned?
> Please find screenshot attached.
>
> Thanks
> John

Hi John,
Thank you for your response.
I have included cable#1 into the calibration and calibrated at the end of it. What is pictured in the first post is the S11 and S21 response of cable#2.
Attached here is a measurement of cable#2 from a high-end vna. The ripple is 0.05db at high frequencies. NanoVNA is far from this.

Also measured a 10db attenuator of a well known brand. Images are attached. The high-end vna produces a perfect flat line. NanoVNA has bad ripples of 0.8dbs.

I have to mention that 1-port calibration in NanoVNA and s11 measuements are exceptionally good. Again, included cable#1 into the calibration. The measurement data from a device perfectly match the high-end vna at 2-3GHz measurement range. That was astonishing and makes this device worth it for s11.

BUT, S21 measurements are not good at all in NanoVNA and not usable. The device offers half of its functionality now. I would say that there is something wrong with the device, if by design, experience and testing should be performing as expected. I would like to receive a feedback, because in this case I should inform the seller of sending it back.

NanoVNA-QT does not implement Enhanced Calibration so the S21 is heavily affected by VNA Port 1 and Port 2 mismatches (expecially in this case, with very low DUT attenuation).

Just try to make the same measurement on the VNA screen (without NanoVNA-QT). Ripple should be lower.

Anyway the best option is to use VNA screen measurement and a "good" 10 dB attenuator on Port 2 (placed also during thru calibration). This should attenuate mismatch to an acceptable level.

As far as I know, NanoVNASaver from version 0.4.0 implements Enhanced Calibration.

Regards, Marco.

Hello,

if you calibrate the NanoVNA with 10 dB attenuator mounted on port 2, the S21 of the cable 2 should not include the 10 dB loss of this attenuator. Your picture seems to include this loss so maybe you did not calibrate with the attenuator already in place.

So: re-calibrate NanoVNA with the attenuator on port 2 and after applying this new calibration you can mearsure S21 of cable 2.

How did you collect the data to prepare the graphs? If data come from NanoVNA-QT, this SW does not implement the full Enhanced Calibration, so part of the ripple will remain caused by usage of this software. Please share the S21 measurement you see on the NanoVNA screen (with attenuator on port 2).

Best Regards, Marco.

Hi Marco,

(My previous post #3330 was sent before your first response)

I have downloaded saver 4.0 and trying to connect to nanoVNA. How can i do this? Drop-down menu in serial port is not populated and 'rescan' doesn't produce any results.

Thanks

Hi
I received my NanoVNA V2 Plus 4 a few days ago. The first unit had a faulty touch screen and I  returned getting the refund via Paypal dispute (seller rejected the return). This is my second order from a different seller from Aliexpress.

The first graph is S11 and S21 with one cable across the ports. It is calibrated with the cheap standards come with it. S21 is completely flat from 1Mhz to 4.4Mhz. Note that there is some impedance mismatch that it is not centered at 50 ohms.  The S11 reflected power  loss seems to improve above 3G and drop again at 3.9G. The impedance mismatch improves using the NanVNA on its own without PC software. But it is not perfectly centered at 50ohms across the wide range of sweep frequencies. Why there is a difference in results using built-in touch screen vs software? What is "enhanced calibration mode"?

The second graph is done with a cheap 10db attenuator. It does not really improve the impedance mismatch in the case of coaxial. Surprisingly It adds more noises to the traces. I know this trick works with measurement of the gain  small signal amplifier using VNA.  I will try repeat this with 3db attenuator to see difference. I tried a 40db attenuator by accident, It would not calibrate with such large attenuator.

The default output power is "3" .
On the oscilloscope, I looked at the square wave forms of NanoVNA V2 plus 4 using zero span or CW, it is "pulsating" square waves as indicated by my TinySA spectrum analyzer. I think the pk-pk voltage is less than 200mV with power setting of 3. Interestingly, my SAA2 also has similar pulsating square waveforms while my Nano-F has steady square waves. I am not sure how this rapid on and off switching of the square waves is a way of generating higher order harmonics...?

The third graph is the noise floor of S11 and S21 with the 50 load attached to the port 1; 1000 data points and averaged over 20 samples per data point. It shows the noise floor of S21 is close 100db up to 3G and 70-80db up 4.4G.  S11 is better than 70db up to 3G and drops to 50 db at 4.4G.

I am having the same problem as noted below. Anyone have a solution?

ed

Dr. Edward P. Sayre, P.E.
President & CTO
North East Systems Associates, Inc.
9 Maple Lane | PO Box 807
Marshfield, MA 02050
[T]: 781-837-9088
[C]: 978-314-4940
esayre@nesa.com

Hello,
Delete all Cypress drivers and install again using the original installer.
Do not update the installed versions via Windows Update!

I have the Nanovna V2 Plus5 version and it's the same.

Hello,

I'm not an expert of NanoVNAsaver or NanoVNA Plus4. Other in this group can help you better than me. I just knew that recent NanoVNAsaver implements Enhanced Calibration. If you want to read something about Enhanced Calibration on NanoVNA V2 and its improvement to the S21 readings, have just a look to this (quite old) message https://groups.io/g/NanoVNAV2/message/225

Anyway, my suggestion is to start using only results from NanoVNA screen (with no external SW). This is useful to isolate the source of the problem you have noticed measuring the cable and the attenuator S21.

Best regards, Marco.

Hello,
I have NanoVNA V2 Plus5.
I don't understand why, but it's the same for me.
Regards, Grzegorz

Thanks Ed for confirming this.

Marco,
I had a look at your post from 2 years ago.
You mention that you measured an attenuator as a DUT. How did you perform the THRU calibration prior to measurements? Did you use another 10db attenuator at port2 or not?

Also, is the full enhanced response that you are referring to in the old post, the 'enhanced response' that is selected in the device?

No, the 10 dB attenuator DUT was mesured without any additional attenuator. In fact the ripple (without Ehnanced Response) is similar to your case. The 10 dB attenuator on port 2 can be useful for measuring S21 of DUT having high S22 reflection.

At that time the full Enhanced Response was not included in NanoVNA FW so the calculation (the expected ehnanced response improvements) was execute in excel. Now yes: enhanced response is a NanoVNA FW option (actually I'm sure for NanoVNA V2 and I think is the same for the Plus4): just enable it.

Best regards, Marco.

Ok.

Which firmware version had you installed back then?

Sometimes it is nothing to do with Cypress driver. It depends on which version of your window OS. My V2 plus 4 works right away on my Window 10 laptop for firmware V0.4.0.

Both my SAA V2 and V2 plus 4 cannot be connected to V0.3.10 with and without Cypress driver.  But my Nano VNA F V2 is happily connected to it!

Vo.4.0 cannot be executed on my Window 8 PC.

I dont think the calibration for the VNA is meant for ultra wide frequency sweep.  In most real world applications like filter and amplifier gain  measurements, If it is calibrated at much narrower frequency range and the 50 load is perfectly aligned at the centre of the Smith chart for all frequencies with the cables..

The attachments show the comparison of noise floor for S21 with calibrated Open versus calibrated Load with 20 samples per point averaging. With a perfect matched load, the system dynamic range  improves by about 10db against a mismatched open.

The 20-sample averaging  improves the dynamic range at least  5db versus 2-sample averaging.

Hi SP8TDH,

Thank you very much for your tip!
I removed the Cypress drivers and didn't install them back. Now, I am able to connect to nanoSaver 4.0 (instructions here: https://groups.io/g/NanoVNAV2/message/1686?p=%2C%2C%2C20 ), AND also the qt_software ( https://nanorfe.com/nanovna-v2-software.html ).

Hi singhonlo,
I am new to this, but as far as I have understood the 'enhanced response' is a feature that is included in the firmware device and increases the sensitivity to low-level signals. The trade-off is increased noise floor.
You may want to check the manual here (page 41): https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwiky4Hfht_3AhWDOuwKHbJBBH8QFnoECA4QAQ&url=https%3A%2F%2Fnanorfe.com%2Fimages%2FV2Plus4_Manual_NC4BR.pdf&usg=AOvVaw3yn1dgaxUHbRKSVM5LJlg9

And a few addded caps.... And its even lower :-)

Dg9bfc sigi



Am 14.05.2022 12:43 schrieb singhonlo <singhonlo@hotmail.com>:

> The attachments show the comparison of noise floor for S21 with calibrated
Open versus calibrated Load with 20 samples per point averaging. With a
perfect matched load, the system dynamic range improves by about 10db against
a mismatched open.
>
> The 20-sample averaging improves the dynamic range at least 5db versus
2-sample averaging.



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