Re: nanovna-users]NanoVNA-H4 2Port calibration problem
Herb,
After thinking having solved the previous problem with NanoVNA-H4 calibration I went on playing. :-D I did a 2port calibration 1MHz- 30MHz in NanoVNA-Saver with the '"S11 Phase"? chart shown and experienced the same problem as with the " S21 gain"? calibration , before calibration a decent display, after calibration no correction on it but all garbadge on the screen, see the picture before calibration attached. I did the measurement on the 50 Ohms standard I had used. Not that I was interested in the phase, but it shoiuld work correctly.
I think Oristo is right, about the communication from NanoVNA-Saver and the device.
Jos
Op 26-1-2020 om 01:24 schreef hwalker:
toggle quoted message
Show quoted text
On Sat, Jan 25, 2020 at 03:58 PM, Jos Stevens wrote:
I did what you suggested , removed the portsavers re-calibrated the standalone VNA,the result was better then before 0.00 db, +0.12 and -0.25 at 50k, 750M and 1500M. Then I calibrated in Nanovna-Saver using 4 segs like you, Before was better, and After was an ideal straight line at 0 dB!
==============================================================================
Good job Jos. I initially had problems with Rune's calibration module but after he posted that you needed to start the module from a good calibration on the NanoVNA saved to "SAVE 0" it has always worked well for me. I still use the ideal models because I hate entering numbers that I don't fully understand.
Rune's NanoVNA-saver application has been working great with the NanoVNA-H4 thus far. The screen saver doesn't work because different code is required for the 4" display, and NanoVNA-saver reports the unit as a NanoVNA-H which may mean the hugen will need to change the -H4 identifier in firmware to help developers differentiate it.
- Herb
|
Before calibrating, perform a reset.? Then select S0 reflection.
Bob
toggle quoted message
Show quoted text
On Sunday, January 26, 2020, 04:07:49 AM PST, Cesar <ea5ioq@...> wrote:
Oristo, thanks a lot! I will try and let you know, best,
°ä¨¦²õ²¹°ù.
|
Re: characteristic impedance
Well there seems to be no concensus about this.? I have a couple of things more to try.
However, starting at the right edge, open circuit, and increasing frequency as the trace swings clockwise, at the 6 o'clock point there is one-eighth wave.? The reactance there, I thought, should be numerically the same as the characteristic impedance.? It's not; it seems to be 50 Ohms regardless (as one responder says).
Continuing clockwise the quarter wave point is reached at the left edge, where impedance becomes resistive and minimum.? So there is no information other than the line length (and attenuation).
Continuing clockwise we return to nearly open circuit at the right edge.? Again, it's resistive but now high impedance.? No information regarding Z.
Of course, terminating the line in a variable resistance shrinks the trace until it becomes a dot regardless of frequency; at that point it's easy enough to read the impedance.? This works (theoretically) for any length line at any frequency.? But it requires the user to adjust the termination.? I can do it that way but was hoping that the eighth wave method would work, eliminating a step that has some potential for error.
Bob
On Sunday, January 26, 2020, 08:50:13 AM PST, W5DXP <w5dxp@...> wrote:
> Bob Albert: When I measure 50 Ohm coaxial impedance with the 1/8 wave method, I always get 50 Ohms.? I tried some 75 Ohm cable and still get 50 Ohms!
Have you tried the 1/8WL open/short method? Where the two Zs cross is the Z0?
|
Re: Wireless control of NanoVNA
Apple locks down the types of
communications that BT can handle to primarily audio-centric A programmable dongle could translate between USB virtual COM and a supported BLE profile. Android doesn't have this limitation My experience writing hardware-specific apps that worked well for many Android devices and generations was a much larger PITA than for iOS. My Android experience with nanoVNA reinforces that.. Most cross-platform solutions end up using WiFi. Stopping and resuming Wi-Fi to minimize interference with VNA measurements is liable to introduce more latencies than by BLE.
|
Re: characteristic impedance
Bob Albert: When I measure 50 Ohm coaxial impedance with the 1/8 wave method, I always get 50 Ohms. I tried some 75 Ohm cable and still get 50 Ohms! Have you tried the 1/8WL open/short method? Where the two Zs cross is the Z0?
|
Re: Wireless control of NanoVNA
iOS bluetooth control may be challenging, Apple locks down the types of communications that BT can handle to primarily audio-centric (with specific exceptions for handshaking apps and Apple's own hardware). To do data transmissions, you could write an audio codec. Since Android doesn't have this limitation, you'd want to have a separate data communication stack for Android. Overall, a big PITA.
Most cross-platform solutions end up using WiFi.
I'd say it'd still be worth it to implement the Android BT communication mode though. It's much easier to 'experiment' in the Android ecosystem.
|
Re: characteristic impedance
On Sun, Jan 26, 2020 at 07:07 AM, Andy UA3RAW wrote:
As it was described by DJ7BA in #8655 message, you must find the lowest (=Lambda/4) resonance frequency. (Impedance there is about 0 Ohm.) One full revolution in the Smith diagram corresponds to a displacement along the line by a distance equal to half the wavelength in it.
So the half-way around, is equal to 1/4 wave length. This is a point of the lowest resonance and it is corresponding to the Marker 1 on your screenshot.
In order to find the characteristic wave resistance of a coax cable, you must find the point that is a half of 1/4 wave length, or 1/8 wave length, and read the reactance at this point. That's why it is called Lambda/8 method.
==============================================================
Andy,
Thanks so much for the clarification. Its something I'll definitely be adding to my engineering notes. Electronics has been both my vocation and avocation for the past 40 years. I still enjoy learning new things, however; few subjects make my eyes glass over as the smith chart does.
At the beginning of my career the company I worked for won a government contract to RF immunity test ignitors to ensure they didn't unintentionally misfire. I had to design rf matching networks for use between our power amplifiers and the ignitors at each test frequency. We brought in the great Christopher Bowick to teach a course on using the smith chart to design matching networks. After that project was completed I never had another practical application to apply what I had learned and as they say "if you don't use it you lose it".
The Lambda/8 method is the first real world application, other than verifying the quality of my solt calibrations or measuring components, that I have used in a while. I wish there was a way of automating the process.
Again, thanks for taking the time to reply. Perfect example of the members helping members format.
- Herb
|
Re: Wireless control of NanoVNA
Bear in mind that WiFi and Bluetooth require a lot of real estate and impose a lot of restrictions on board layout. - Ed
|
Re: available screens for the nanovna
3.2 inch is the biggest.?
Why not just replace the touchscreen?
Use an xacto knife to cut around the outside edge of the display to remove the old touch surface and just bond a new 3.2 inch touchscreen to the display.?
In fact, if you have an old junk Palm Pilot ot MP3 player that has a resistive touch surface, try that.
On Sun, 26 Jan 2020 at 10:02 AM, nanovnauser@...<nanovnauser@...> wrote: HI all,i have a nanovna that i replaced the screen on with a 3.2 inch version that i got from china,it worked fine untill i cracked the screen,now the touchscreen doesent work,i need to buy a replacement,whats the biggest i can get for this?,cheers in advance .73.
|
Re: characteristic impedance
On Sun, Jan 26, 2020 at 04:50 PM, hwalker wrote: Since the actual method has always worked for me I didn't give it any
deeper thought. If the terminology I used needs correcting please add to the
discussion so I can correct my notes and not perpetuate incorrect information
(i.e. if that point is 1/4 wave length why is it called the 1/8th method).
- Herb
Ok Herb, I'll try. As it was described by DJ7BA in #8655 message, you must find the lowest (=Lambda/4) resonance frequency. (Impedance there is about 0 Ohm.) One full revolution in the Smith diagram corresponds to a displacement along the line by a distance equal to half the wavelength in it. So the half-way around, is equal to 1/4 wave length. This is a point of the lowest resonance and it is corresponding to the Marker 1 on your screenshot. In order to find the characteristic wave resistance of a coax cable, you must find the point that is a half of 1/4 wave length, or 1/8 wave length, and read the reactance at this point. That's why it is called Lambda/8 method.
|
available screens for the nanovna
HI all,i have a nanovna that i replaced the screen on with a 3.2 inch version that i got from china,it worked fine untill i cracked the screen,now the touchscreen doesent work,i need to buy a replacement,whats the biggest i can get for this?,cheers in advance .73.
|
Re: First PCB pictures of the V2
On Thu, Jan 2, 2020 at 01:38 PM, Mel wrote:
As you want to use only ¡®standard¡¯ components those 50Ohms resistors have
typically a bad impedance behaviour at higher frequencies due to their high
parasitic inductance¡
Have you tried to solder the resistors upside down such that the resistive element is on the same plane as the trace? I have not tried it but it seems that it would improve the behavior of all low value resistors connected to transmission lines. Just a suggestion, maybe not easy to implement in practice with automated assembly unless you have the parts re-reeled. Didier -- Didier Juges KO4BB.com
|
Re: nanovna-users]NanoVNA-H4 2Port calibrationof
Herb,
I fully agree with your comments,? the NanoVNA is an excellent device and definitely on the money, I read on giithub that Hugen even has idea's to improve the impedance of CH1 !!
When hardware changes are neccessary for that (component changes) , I wonder if I dare to open this nice case.
Best Regards
Jos
Op 26-1-2020 om 14:25 schreef hwalker:
toggle quoted message
Show quoted text
On Sun, Jan 26, 2020 at 04:38 AM, Jos Stevens wrote:
"This is an eye opener for me, it appears that at start NanoVNA-Saver is using the C0 calibration of NanoVNA, untill now I thought these calibrations were independant."
- It always helps to get a different perspective from someone else. Especially true when you are doing everything "right" and you still get unexplainable results.
"I just made a new 100 Segs calibration. Please see the attached results."
- Your after calibration thru results are definitely on the money.
" NanoVNA-H4 is a great device, just the CH1 impedance could be a bit better and the enclosed 50 Ohms standard I measure (4 point measurement @ 10kHz) 50.940 Ohms, also could be a bit better, I use one that I previously received wich I measure 49.850 OHms and correct it in NanoVna-Saver's "Calibration" window. Yes I can do that for the portsavers also."
- For $60 usd delivered via parcel post, you can't expect too much better quality than what is already in the package. The terminator actually measures better than some name brand units I have, and the return loss is very well behaved. I always keep in mind that hugen developed the NanoVNA to "to attract more young people to pay attention to radio frequency and wireless" and that tempers my expectations regarding any meteorologist level performance. The volume of sales world wide over the past few months indicates he not only has attracted some youngsters to RF measurement techniques, but given some of us older people access to measurement capability that we previously lacked.
Regards,
- Herb
|
For driver documentation testing, I installed Python 3.7.6 from Windows 10 Microsoft Store. Unlike much Windows software, Microsoft Store only installs apps separately for each user on a PC. This allows duplicating bugs: 1) the installed pip hangs after successful completions, requiring e.g. [Ctrl]+[C] This is addressed by: python -m pip install -U pip (requiring Ctrl+C after e.g. "Successfully installed pip-20.0.2") ... also, to run scripts e.g. for nanoVNA: pip install pyserial pip install numpy pip install pillow 2) My scripts, which worked on both older and newer versions installed from other sources were broken by this Python version. That was addressed by changes pushed to GitHub: If folks are interested in a version of screenV.py for Hugen's larger H4 screens, as modified by Herb Walker: /g/nanovna-users/message/10096 .. let me know what name is wanted for that bigger screen script. Now, for the >>really weird<< part. The first few times this screen copy script is run, after changing "COM3" in screenV.py to your virtual COM port, e.g. python screenV.py foo .. it will hang, because this Python version will not return enough data. This is repeatable by adding another Windows 10 user and reinstalling Python from Microsoft Store... If you want, this can be observed in screenV.py by commenting line 61 and uncommenting lines 62-65. The workaround: * Ctrl+C and rerun the script a few times until it DOES work. After a first success, the script always works thereafter..??!! Bottom line: * despite its popularity, Python is neither robust nor stable.
|
Re: characteristic impedance
On Sun, Jan 26, 2020 at 04:51 AM, Andy UA3RAW wrote:
Herb, it seems to me that a half-way around the smith chart is 1/4 wave length. Isn't it? )))
=========================================================================
Andy,
You may be able to put it in better terms than I did, as I was only parroting back what I understood from the original poster. I have only used smith charts sparingly in my career. The key thing that stuck in my mind was the original poster saying the 1/8 method started from the same position as a short on the first revolution around the smith chart.
Since the actual method has always worked for me I didn't give it any deeper thought. If the terminology I used needs correcting please add to the discussion so I can correct my notes and not perpetuate incorrect information (i.e. if that point is 1/4 wave length why is it called the 1/8th method).
- Herb
|
Re: nanovna-users]NanoVNA-H4 2Port calibrationof
Oristo,
Thanks for your information abt. the serial port, actually I am using a version 3.1 comport and sofar I saw no problems in comunicating with theNano VNA-H4 , with the firmware as supplied by Alibaba.
This problem was sollved by executing a new device stand alone calibration and saving it to CH0 of the device.
Best Regards
Jos
Op 26-1-2020 om 14:03 schreef Oristo:
toggle quoted message
Show quoted text
it appears that at start NanoVNA-Saver is using the C0? calibration of Yes
NanoVNA, untill now I thought these calibrations were independant. No, USB serial communication from nanoVNA to Python is not reliable for
all firmware, USB cables and versions of Python.
Using a USB 2.0 (rather than 3.0) port e.g. by hub sometimes helps.
Adding ferrite beads to USB cable may help.
Some firmware and Python serial implementations are simply flakey.
Rune's workaround is to depend on nanoVNA C0 calibration returning data values nearly correct.
|
Re: nanovna-users]NanoVNA-H4 2Port calibrationof
On Sun, Jan 26, 2020 at 04:38 AM, Jos Stevens wrote:
"This is an eye opener for me, it appears that at start NanoVNA-Saver is using the C0 calibration of NanoVNA, untill now I thought these calibrations were independant."
- It always helps to get a different perspective from someone else. Especially true when you are doing everything "right" and you still get unexplainable results.
"I just made a new 100 Segs calibration. Please see the attached results."
- Your after calibration thru results are definitely on the money.
" NanoVNA-H4 is a great device, just the CH1 impedance could be a bit better and the enclosed 50 Ohms standard I measure (4 point measurement @ 10kHz) 50.940 Ohms, also could be a bit better, I use one that I previously received wich I measure 49.850 OHms and correct it in NanoVna-Saver's "Calibration" window. Yes I can do that for the portsavers also."
- For $60 usd delivered via parcel post, you can't expect too much better quality than what is already in the package. The terminator actually measures better than some name brand units I have, and the return loss is very well behaved. I always keep in mind that hugen developed the NanoVNA to "to attract more young people to pay attention to radio frequency and wireless" and that tempers my expectations regarding any meteorologist level performance. The volume of sales world wide over the past few months indicates he not only has attracted some youngsters to RF measurement techniques, but given some of us older people access to measurement capability that we previously lacked.
Regards,
- Herb
|
|
|
Re: nanovna-users]NanoVNA-H4 2Port calibrationof
it appears that at start NanoVNA-Saver is using the C0? calibration of Yes NanoVNA, untill now I thought these calibrations were independant. No, USB serial communication from nanoVNA to Python is not reliable for all firmware, USB cables and versions of Python. Using a USB 2.0 (rather than 3.0) port e.g. by hub sometimes helps. Adding ferrite beads to USB cable may help. Some firmware and Python serial implementations are simply flakey. Rune's workaround is to depend on nanoVNA C0 calibration returning data values nearly correct.
|
Re: First PCB pictures of the V2
MAX2870. Maxim has an oscillator chip MAX2870, which gives from 23MHz to 6GHz. Digikey says it costs 10?€$ whatever. I know this is too late for this version but maybe in the future, and then there are probably new chips available.
|
Oristo
Andy UA3RAW