NanoVNA Custom Software

[Flynt]

Thanks Wim
I've already written a private message to joeqsmith, to know how to get it ...

I'm not able to program...

[_Wim_]

I think this software is a good alternative to what joeqsmith has made:

https://github.com/mihtjel/nanovna-saver

[_Wim_]

The executable can be downloaded from here if you do not want to run it in phython (download the zip file)

https://github.com/mihtjel/nanovna-saver/releases

[radiolistener]

Can you try a calibration with all cables and connectors that will be used in place ?
Other than the needed calibration items of course

The problem here is that all calibration loads should be connected through the same length as 500 Ohm terminator.

Here is my calibration kit and 500 Ohm terminator:


As you can see, it's about 15 mm longer than calibration terminators. It leads to additional delay in wave propagation and as result it leads to measurement error.

You can check my previous S1P file for 500R terminator, see Group Delay S11, it's about 0.25 ns.

Now I tried to setup ELECTRICAL DELAY = 247 picoseconds (see SCALE menu in NanoVNA) to get software correction for that delay. I tried different values and 247 ps give me the best result. So it seems like these 15 mm leads to 247 ps delay. And now, with 247 ps delay correction, I get much better result

Series RLC:


Parallel RLC:


Group Delay S11:


S11:


VSWR:

[radiolistener]

Here is another finding. When I tried to get the same measurement (with electric delay 247 ps) for 500R terminator with no connection to PC (powered from accumulator), it shows 500 Ohm and VSWR=10 almost up to 900 MHz.

For example:
600 MHz: Rs = 550 Ohm, VSWR = 11.07
700 MHz: Rs = 501 Ohm, VSWR = 10.03
800 MHz: Rs = 478 Ohm, VSWR = 9.62
900 MHz: Rs = 462 Ohm, VSWR = 9.08

So, it seems that USB connection to PC affects measurements...

Tried more tests about that. When I connect it to powered off power bank, there is no influence, but after power on, there is a change in measurement above 500 MHz. It seems that external power supply leads to increase power supply voltage and it affects measurement.

I tried to calibrate it with external power supply, but it seems, that calibration cannot eliminate measurement error which appears with external power supply. So, the only way to get the best measurement is to disconnect device from external power supply. Very strange. Any idea how to fix it?

[rhb]

I checked the pinout of  the STM32F303CCT6 with 48 KB of RAM and 256 KB of flash today and it should be a drop-in replacement for the existing STM32F072CBT6.  The 3x increase in RAM and 2x increase in flash would allow a substantial increase in features such as TDR, storing multiple calibration ranges, etc.  The groups.io list is a firehose of activity.

I was going to do the chip swap myself, but one of the sellers, hugen, has offered to provide a unit with the '303 part.  I expect that will be very popular with people wanting to write FW with additional features.  So I'm hoping for an announcement that '303 based units are available for  an extra $5-10 US.  In quantity 2400 from Digikey, the price differential is $1.28 US.  $1.92 vs $3.20 for the MCU.  That makes it an attractive change for an OEM if it allows more features.

The 16 KB memory of the current versions is a significant limitation.  An important application for the additional memory is TDR from VNA data. There are already multiple implementations for producing TDR traces from VNA data being done on a PC, but no room for it on the device.

The existing FW should run on the larger part unaltered, so buying a unit with the STMF303 part  makes it easy for a buyer who is not interested in writing FW to do updates as things develop.  This is the RF version of the $20 LCR-transistor tester.  Hang on to your hats!

Have Fun!
Reg

[rhb]

Here is another finding. When I tried to get the same measurement (with electric delay 247 ps) for 500R terminator with no connection to PC (powered from accumulator), it shows 500 Ohm and VSWR=10 almost up to 900 MHz.

For example:
600 MHz: Rs = 550 Ohm, VSWR = 11.07
700 MHz: Rs = 501 Ohm, VSWR = 10.03
800 MHz: Rs = 478 Ohm, VSWR = 9.62
900 MHz: Rs = 462 Ohm, VSWR = 9.08

So, it seems that USB connection to PC affects measurements...

Tried more tests about that. When I connect it to powered off power bank, there is no influence, but after power on, there is a change in measurement above 500 MHz. It seems that external power supply leads to increase power supply voltage and it affects measurement.

I tried to calibrate it with external power supply, but it seems, that calibration cannot eliminate measurement error which appears with external power supply. So, the only way to get the best measurement is to disconnect device from external power supply. Very strange. Any idea how to fix it?

My first guess would be EMI coming in on the power cable.  Does the cable you're using have chokes?

[tautech]

The sweep width and the few data points available is also a significant limitation on accuracy. Joe showed this earlier where the interpolation with so few points had it drawing a series of straight lines on the Smith chart.
The user needs keep this data point limitation firmly in mind and use a sweep width that's appropriate and a heap of averaging if necessary.

[radiolistener]

My first guess would be EMI coming in on the power cable.  Does the cable you're using have chokes?

I also thought about it. But this is not the case. I can connect any length of cable and it doesn't affect measurement. Also I tried to connect cable to power bank with disabled output and it doesn't affect measurement. But when I press power on button on power bank, it leads to measurement error. So, the the issue appears when external voltage is applied and don't depends on the cable.

[radiolistener]

After some period of time I found that cable influence disappears.  May be it happens when battery is charging. And when battery is full this effect disappears.

Here is 500 Ohm terminator measurement with 247 ps correction for wave propagation delay in SMA-SMA adapter:



Now it looks great 


By the way, my NanoVNA has 3.7V 450 mAh battery and can work from battery up to 130 minutes.

[rhb]

You probably should probe the output of U3 with a scope and DMM and see what Vdd looks like with and without external power.

The +5 V connection on terminal 3 of U3 looks as if it would power the whole board any time the USB had 5 V unless it's an unconnected power input.  But it looks to me as if it is coming from the USB.  So I'm a bit puzzled by the schematic.

[radiolistener]

Confirmed. Measurement is affected when battery is charging.
When charge LED stops flashing, measurement error disappears.

I tried to measure voltage between GND and VDD on ST-LINK connector.

When powered from the battery: 3.3350 V
When external power connected: 3.3306 V
After some time with ext. power: 3.3325 V (measurement error is still present)
When charge LED stops flashing: 3.3339 V (measurement error disappears)

[joeqsmith]

Someone had posted this comment about torque wrenches.  This is my super expensive torque wrench calibration station.   The bolt that holds the scale and hex standoff is mounted on two ball bearings that were clamped in the Panavice.   The steal is very close to 1lb.      Lower right, you can see the screwdriver style and my modified deep wall socket.  Also my ultra thin spanner that is used to hold some of the SMA parts, when using the torque wrench.   

After reading their comment, I would be very interested in knowing how much other SMA torque wrenches vary as they describe.  As I note, mine is about 1" and you need to choke up on the rubber to get to 8".   I could see more error in the technique used if you didn't follow the instructions.   

[hendorog]

Confirmed. Measurement is affected when battery is charging.
When charge LED stops flashing, measurement error disappears.

I tried to measure voltage between GND and VDD on ST-LINK connector.

When powered from the battery: 3.3350 V
When external power connected: 3.3306 V
After some time with ext. power: 3.3325 V (measurement error is still present)
When charge LED stops flashing: 3.3339 V (measurement error disappears)

Very interesting discovery. I had not heard of that and it might explain a few issues people are having comparing similar devices.

I'll try and replicate as all of my testing has been done with the devices plugged in.

[KE5FX]

Choking up on the wrench should make no difference to the breakover torque.  That's the whole idea behind a torque wrench. 

That said, it does make a subtle difference regarding how the force is applied.  There is one right way and (numerous) wrong ways to use a torque wrench (actually two wrenches) on high-grade connectors.  A great operator training guide was created for UC Berkeley students at one point but I couldn't find a straightforward .PDF edition, just a bunch of skeevy links to "slide sharing" sites and (with some effort) the original PowerPoint file.  I went ahead and printed it to a .PDF, linked here (61 pages, 6 MB).

Highly recommended reading even if (like me) you blow off 80% of these guidelines in day-to-day use.  At least you will know what you're doing wrong. 

[joeqsmith]

Choking up on the wrench should make no difference to the breakover torque.  That's the whole idea behind a torque wrench. 

That said, it does make a subtle difference regarding how the force is applied.  There is one right way and (numerous) wrong ways to use a torque wrench (actually two wrenches) on high-grade connectors.  A great operator training guide was created for UC Berkeley students at one point but I couldn't find a straightforward .PDF edition, just a bunch of skeevy links to "slide sharing" sites and (with some effort) the original PowerPoint file.  I went ahead and printed it to a .PDF, linked here (61 pages, 6 MB).

Highly recommended reading even if (like me) you blow off 80% of these guidelines in day-to-day use.  At least you will know what you're doing wrong. 

[joeqsmith]

I had mentioned in the last video I made about the limited resolution (distance) when making TDR measurements.    I talked a bit about how you may be able improve it but with it being a $50 unit, I don't see much of a point.   Well except for the pure fun of it.....

So I talked it over with a friend of mine and we had a good laugh about the whole project.  He offered one idea that should help improve the setup but it's all a guess if the Nano can actually be used this way and get any useful information from it.   Of course, cost will need to be ignored which is part of the humor.... 
 
First baby step,  modify my software to support the range extender.   It may not look like anything is going on in the attached plot, but what you see the Nano using Channel 1 for S11.  That's not a misprint.   Granted, it's only 100MHz.       Like I said, baby step.   

***
Should mention, yes, it is indeed a 100 ohm resistor. 

[joeqsmith]

If you read the document you linked, on page 14, they show the hand placement.  That is the marking that the person commenting on my video mentions.   He is absolutely correct that it will have an effect which is why this training manual talks about it.  Page 15, they show the damaged connector after the person chokes up on the wrench.   

What I would like to know is how much of an effect various wrenches have.  I only have the one click type. 

[KE5FX]

If you read the document you linked, on page 14, they show the hand placement. 

Yes, together with the completely bogus reasoning that it has anything to do with the grasping point along the moment arm. 

It's still a good document, IMO, despite that.

That is the marking that the person commenting on my video mentions.   He is absolutely correct that it will have an effect which is why this training manual talks about it.  Page 15, they show the damaged connector after the person chokes up on the wrench.   What I would like to know is how much of an effect various wrenches have.  I only have the one click type.

I've always found that I can apply pretty much whatever torque I want by holding it in a certain (incorrect) way, whether dealing with a ratchet or an open-ended torque wrench.  The angle at which you apply the force is important, but the distance along the handle considered by itself is not.

[joeqsmith]

Again, you can lead the horse to water....  But I can't help you. 

[hendorog]

If you read the document you linked, on page 14, they show the hand placement. 

Yes, together with the completely bogus reasoning that it has anything to do with the grasping point along the moment arm. 

It's still a good document, IMO, despite that.

That is the marking that the person commenting on my video mentions.   He is absolutely correct that it will have an effect which is why this training manual talks about it.  Page 15, they show the damaged connector after the person chokes up on the wrench.   What I would like to know is how much of an effect various wrenches have.  I only have the one click type.

I've always found that I can apply pretty much whatever torque I want by holding it in a certain (incorrect) way, whether dealing with a ratchet or an open-ended torque wrench.  The angle at which you apply the force is important, but the distance along the handle considered by itself is not.

Hmm, I am not so sure. I think that the position of the force you apply to the handle will matter - because of the construction of the wrench. The breaking 'knuckle' is offset from the centre of rotation of the nut.

So there are two levers involved- one from your hand to the nut, and a shorter one from your hand to the knuckle.

If you were to use the wrench and measure the exact force to the end of the handle to break the knuckle, then:
Reduce the hand-knuckle lever length to 10% of what it was, then obviously you will need to apply 10 times more force to break the knuckle. Force x distance.
Now 10 times more force is being applied to the end of the hand-nut lever. The lever is shorter than it was, but it is not 90% shorter because of the nut-knuckle distance hasn't changed.

That is also the case - but with a smaller nut to knuckle distance - in the posted video.

[KE5FX]

That is also the case - but with a smaller nut to knuckle distance - in the posted video.

But that's a different moment arm than the one shown in the document.

As long as you hold the torque wrench somewhere along the actual handle (i.e., the red part shown here, using the model of torque wrench I have here as an example) you will be able to deliver the specified torque or something very close to it.  It (should) go without saying that if you grab the wrench just behind the knuckle, you can apply pretty much whatever force you want in whatever direction you want. 

[joeqsmith]

I like this website for practical information:

https://www.microwaves101.com/encyclopedias/torque-wrench
https://www.microwaves101.com/encyclopedias/connector-care

[radiolistener]

It seems that CH1 on my NanoVNA has not so good VSWR, is it ok?

[hendorog]

That is also the case - but with a smaller nut to knuckle distance - in the posted video.

But that's a different moment arm than the one shown in the document.

Same principle applies, just different dimensions.

As long as you hold the torque wrench somewhere along the actual handle (i.e., the red part shown here, using the model of torque wrench I have here as an example) you will be able to deliver the specified torque or something very close to it.  It (should) go without saying that if you grab the wrench just behind the knuckle, you can apply pretty much whatever force you want in whatever direction you want. 

Makes sense to me - as long as it's designed for that usage, so that it stays it in the torque range its spec'd for - or at least not far enough out of range to break stuff if you aren't doing critical stuff.