NanoVNA Custom Software

[joeqsmith]

I haven't measured how much input power the Nano can handle before it starts to compress.  Looking at the output signal with a calibrated SA, it was fairly close -9 to -13dB called out in the manual.   It's far from flat.     

The transistor will have a gain of 14dB or so.  -20dB should keep me from out of the non-linear region.   

Replacing the thru section of the cal standard with our test transistor and increasing the bias, we can measure the the gain. 

[TheSteve]

I don't know the specs but the price seems right and they are from a serious RF company. Could they possibly be useful?
https://www.ebay.com/itm/Anritsu-MM700022A-Microwave-Switches-Lot-of-2/173844545453

[joeqsmith]

I don't know the specs but the price seems right and they are from a serious RF company. Could they possibly be useful?
https://www.ebay.com/itm/Anritsu-MM700022A-Microwave-Switches-Lot-of-2/173844545453

Maybe.   Someone would need to look up the datasheets for them.    If you read the posts, again I have a transfer relay that I could easily bolt on but that's not the goal.   

As I mentioned, I have an old transfer relay that I could easily drop in and use but my goal wasn't to just show an old relay connected to the Nano like the video I had linked.  That video doesn't show anything about how it is actually used and I doubt many people would want to see me just connect a relay.   I would like to sort out something cost effective that could be replicated.   

****
Cleanup....

I'm not sure how you would use them.  This is more like what you would want if you were looking for used.  Again, you would need to find the datasheet.  Then being used, it may no longer meet the specified performance.
https://www.ebay.com/itm/RF-Transfer-Relay-with-Suppress-Switch-CS-37S10-DM/163664843937?hash=item261b2f54a1:g:74QAAOSw9Mtcwcod

[Bicurico]

Just a dumb question, sorry if it is stupid.

From what I understood, you want to switch S1 and S2 for different measurements, without having to screw the cables on/off.

Wouldn't a cheap DiSEqC-switch as used for satellite TV reception do the job? The controller that implements the DiSEqC switching could be replaced by some simple logic (press button or whatever).

These switches are optimized for 950MHz-2150MHz, but will handle lower frequencies for sure. They come in all shapes and forms (2 in - 1 out up to 16 in - 1 out or even 16 in - 16 out).

https://en.wikipedia.org/wiki/DiSEqC

Again, sorry if this does not make sense, if so, please explain in a friendly way.

Regards,
Vitor

[Bicurico]

Sorry: just remembered that TV/CATV/SAT is 75 Ohm and not 50 Ohm.

Regards,
Vitor

[joeqsmith]

My old antique 70's HP VNA may be a relic but it has some nice features, like a DC-3GHz step attenuator.  Sadly, I don't have one just laying around.

Wanting to get some idea where things start to compress (nano + amp)  one attenuator was removed from the drive but it had little effect.   The second 10dB attenuator was then swapped out for a 3dB part and the test was repeated.  We can see it's now about 2dB low.   

[joeqsmith]

I suspect the compression is not the DUT but the Nano being over driven.  The Nano would be putting out somewhere below 10dB which shouldn't be a problem for our DUT.   I didn't see in the Nano's manual where they talk about at what point it starts to go nonlinear.   I doubt people care about it. 

To sort it out,  this is the crappy setup.  The whole thing is really a bad outside of a great setup for learning the basics.  It's not something you would want to try and use.   To see if the Nano is compressing, I would like to add a 10dB attenuator after the bias T and see if we get our 16dB back. 

So this nightmare of error prone mess was placed between the DUT and transfer relay.  Ideally I would characterize it, but I really just want to know it we get our gain back.   The large part is a commercial bias T followed by a Midwest BNC style 10 dB attenuator. 

I ran this with the thru and stored that as my reference then repeated the test using our DUT.

Hard to say how the different flavors of Nanos behave or what would be a safe region to use.   

[joeqsmith]

Just a dumb question, sorry if it is stupid.

From what I understood, you want to switch S1 and S2 for different measurements, without having to screw the cables on/off.

....

Again, sorry if this does not make sense, if so, please explain in a friendly way.

Regards,
Vitor

Yes, I want to flip the cables without disturbing the test setup in order to measure all four S parameters.    This is the job of the transfer relay.   If you want to use two coaxial SPDT relays, you will need to sort out how to combine the signals.  The stub may burn you as well.   

Looking at the picture showing the inside of my HP test set, you can see the transfer relay and step attenuator.  Sitting between them is a SPDT relay.  This relay will terminate the unused pin rather than float it.    Point being if you are going to buy some used relays to make some sort of test set, make sure you locate and read the datasheets first. 

[joeqsmith]

Corrected post to include the picture showing the test setup.   

https://www.eevblog.com/forum/rf-microwave/nanovna-custom-software/msg2638257/#msg2638257

[joeqsmith]

I located the original articles I mentioned that talk about using the S-parameters with SPICE.   

[joeqsmith]

The first attached graph shows S21 while sweeping the collector current .   A bit odd as the gain dips sharply when the current is very low.   There is no amplification until roughly sweep 112. 

The second graph is the same setup but driving the DUT a bit harder and zooming in.  The datasheet shows the 1dB compression at 100MHz is roughly 17.5dB.   You can clearly see it has started to compress at 19.

[erikka]

If I make no mistake interpreting the nanoVNA schematic and the datasheets of the SA612 and the ADC you have to stay below about -10dBm for P2.
The SA612 amplifies about 17dB (below 500MHz). The max input level to the ADC is about 0dBm and the resistor network at P2 reduces the level with about 6dB. Or am I making a mistake?

[joeqsmith]

If I make no mistake interpreting the nanoVNA schematic and the datasheets of the SA612 and the ADC you have to stay below about -10dBm for P2.
The SA612 amplifies about 17dB (below 500MHz). The max input level to the ADC is about 0dBm and the resistor network at P2 reduces the level with about 6dB. Or am I making a mistake?

https://www.eevblog.com/forum/rf-microwave/nanovna-custom-software/msg2598729/#msg2598729

[erikka]

I was not aware the output spec is the same as the input spec. Please ignore my post 

[joeqsmith]

I was not aware the output spec is the same as the input spec. Please ignore my post 

... I didn't see in the Nano's manual where they talk about at what point it starts to go nonlinear.   I doubt people care about it. 
...
Hard to say how the different flavors of Nanos behave or what would be a safe region to use.   

It should be safe to say it supports a thru without distortion or what would be the point of running a SOLT.   From playing with that transistor, we can get some idea but I haven't looked into it any further.  Staying below the output level should be safe but the dynamic range of the Nano is pretty limited.  My low cost transfer relay certainly doesn't help with this.   

[joeqsmith]

Plot showing all four S parameters.    This data was collected automatically using the low cost transfer relay, after running a full 2-port calibration.   The T-check was installed as the load. 

[joeqsmith]

1000 mating cycles, I like that.

https://youtu.be/U3Fabnw9U04?t=40

[battlecoder]

I just started following this thread since I'm interested in getting a nanoVNA, and you've done such an impressive work. Thanks for sharing all the research and tests you've done on this device!

[joeqsmith]

I just started following this thread since I'm interested in getting a nanoVNA, and you've done such an impressive work. Thanks for sharing all the research and tests you've done on this device!

No problem.  Glad you are finding them of interest. 

In the attached plot, the Nano is used to monitor the effects of applying corona dope to a 5 pole low-pass filter and watching it dry.

The filter was attached to the transfer relay after cal, then used as a baseline.  The plot is the deviation from that baseline. 

The first few sweeps (towards the back), it is reasonably flat with a clean PCB.  The deep blue is after applying the liquid dope.    As it slowly drys, I would expect it to return to normal once fully cured.   

[z33t]

Hello,
Can You tell me what "CORRECTION" does to NanoVNA, plase?
It seems that it is something like 10 dB attenuator, but I am not sure.

"CORRECTION" is in "CAL" menu.
Thanks

[joeqsmith]

Hello,
Can You tell me what "CORRECTION" does to NanoVNA, plase?
It seems that it is something like 10 dB attenuator, but I am not sure.

"CORRECTION" is in "CAL" menu.
Thanks

It's just an easy way to enable / disable the correction factors created after the unit was calibrated.   

[z33t]

Thanks

[z33t]

I have made comparison between Rohde Schwarz and NanoVNA.
The same homemade VHF Helical Band-Pass filter was measured with both instruments.
The results was amazing!
Here is the pictures:

[joeqsmith]

Looking good. 

[joeqsmith]

Someone had asked me about making one more video for the Nano.   As I said in the attached, I am not apposed to it if there is some interest.   Feel free to chime in if there is something else you would like to see.