Re: Common ground and 2-port measuring
Actually, that's a common, but incorrect statement. Current - RF or otherwise - always flows along ALL available paths, split according to the inverse of the resistance.
To make it simple, let's say there are two paths. One has 10 ohms resistance and one has 5 ohms resistance. If you apply 10V to the circuit, 1amp will flow though the first path and 2 amps though the second path.
The same goes for milliohm paths like those found in grounds.
Jerry, AI0K
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Re: Common ground and 2-port measuring
Tnx Dave!
Nice and short write-up of what's happening.
73
Arie PA3A
Op 8-7-2022 om 19:57 schreef DP:
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RF return current always flows via the path of least reactance. Here's more info:
Dave NU8A
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Re: Fake NanoVNA? Or short between the headset :)
I put here my log of the installation on Windows but this log is in French. I can send it to you in Word if you want to translate it.
At home 2 drivers coexist, each creating a different com port from the USB interface. The log shows that only when Windows detects a device on the USB port loads the correct driver. It is impossible to preload the miscellaneous. Obviously this diver must be present on the disk for Windows to look for it.
--
F1AMM Fran?ois
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-----Message d'origine-----
De la part de Tim Dawson
Envoy¨¦ : samedi 9 juillet 2022 21:54
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Re: Fake NanoVNA? Or short between the headset :)
Are you certain that you have the correct port selected for the NanoVNA? And are you certain that the software on the NanoVNA is reasonably current?
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On July 9, 2022 1:34:23 PM CDT, Douglas Butler <sherpadoug@...> wrote: In about 75 seconds the NanoVNA Saver main screen finally shows up. But when I try to connect to the VNA comm port it quickly times out:
NanoVNASaver.Hardware.NanoVNA_2 - ERROR - Timeout reading version registers. Got: b' '
NanoVNASaver.Controls.SerialControl - ERROR - Unable to connect to VNA: Timeout reading version registers
<more debug stuff if you want it>
This is on a freshly booted NUC i5 2.2GHz 16GB RAM 64 bit Win 10 Pro
VNA-qt runs so the VNA, USB cable, etc are OK.
--
Sent from my Android device with K-9 Mail. Please excuse my brevity.
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Re: Fake NanoVNA? Or short between the headset :)
In about 75 seconds the NanoVNA Saver main screen finally shows up. But when I try to connect to the VNA comm port it quickly times out:
NanoVNASaver.Hardware.NanoVNA_2 - ERROR - Timeout reading version registers. Got: b' '
NanoVNASaver.Controls.SerialControl - ERROR - Unable to connect to VNA: Timeout reading version registers
<more debug stuff if you want it>
This is on a freshly booted NUC i5 2.2GHz 16GB RAM 64 bit Win 10 Pro
VNA-qt runs so the VNA, USB cable, etc are OK.
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Re: Fake NanoVNA? Or short between the headset :)
On Fri, Jul 8, 2022 at 03:07 PM, <jetmech@...> wrote:
I purchased a NanoVNA off of Amazon. Seem to work when I got it, but then
when I tried to calibrate it I'm able to. I even tried updating the firmware.
I exchanged it for another one and this time It will not calibrate at all. I
tried using the RF Demo kit as well. I got the -H, but the RF Demo kit says
its for the -F, did I kill the NanoVNA using the -F RF Demo kit?
The replacement when using the smith chart doesn't move from center even with
open or shorted cap.
There is no problem using the RF Demo kit with any NanoVNA. If you are having calibration problems check the cal loads with a DMM to make sure you have an open, load and short. Calibrate right on the NanoVNA and only use the cable for the through cal. When doing a cal make sure your RESET the calibration before you start and SAVE to one of the slots when done. After cal check with your loads on the Smith chart. Short on far left, 50 ohm in middle and open on far right. Roger
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Re: Fake NanoVNA? Or short between the headset :)
On Sat, Jul 9, 2022 at 09:36 AM, Mike Millen wrote:
I think you'll find if you leave that black window a bit longer, then
NanoVNA will load... it's a slow starter, that's all.
NanoVNA Saver was written in python and all the necessary files to run are "packaged" in the .exe file. Each one is scanned by the virus scanner and it takes a long time to load because of this. On slower machines the "black window" will be there for 15 to 20 seconds before the Saver screen appears. Roger
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Re: Fake NanoVNA? Or short between the headset :)
I think you'll find if you leave that black window a bit longer, then NanoVNA will load... it's a slow starter, that's all.
Mike
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On 09/07/2022 16:12, Douglas Butler wrote: I mostly use the box alone. NanoVNA-saver refuses to run on my PC (Win10pro, just gives a black window). I have tried VNA-qt, and the big screen is nice, but -qt lacks some features available on the box itself. Is there a more powerful client I should try, or help getting -saver to function?
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Re: Fake NanoVNA? Or short between the headset :)
I mostly use the box alone. NanoVNA-saver refuses to run on my PC (Win10pro, just gives a black window). I have tried VNA-qt, and the big screen is nice, but -qt lacks some features available on the box itself. Is there a more powerful client I should try, or help getting -saver to function?
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Re: Fake NanoVNA? Or short between the headset :)
My nanoVNA is also from Amazon but it's a nanoVNA-F. I did not sound the difference with your -H.
Using the box alone is crazy. I advise you to use it through nanovna-saver. It's a bit of a hassle to connect the COM port via USB, but then it's a joy. The calibrations are done from nanovna-saver and you will no longer have to touch the box (except for the connecting straps, of course).
--
F1Amm Fran?ois
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Re: Fake NanoVNA? Or short between the headset :)
There is no difference in calabration kits except maybe different connectors.
Clyde KC7BJE
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Re: Common ground and 2-port measuring
Respectfully, I think measuring a CM choke is being overly complicated in this discussion. The common mode Z is measured just as if the CM choke was an inductor or capacitor. Either measure it with an S11 measurement (shield to shield leaving the center conductor alone or short the input terminals and output terminals together) across Port 0 or do an S21 Thru method getting the insertion loss and the phase angle (input shield to port 0 center conductor and output shield to port 1 center conductor leaving the center conductor of the coax alone. If bifilar-wound, short the input terminals together at port 0 and the output terminals together at port 1 OR determine which conductor is common to in and out and use that conductor only).
If it is necessary to use port 0 and 1 to measure insertion loss just do an S21 with the CM choke connected as if the core wasn't there as the core is immaterial for a CM choke's loss (not so for a bifilar-wound CM choke because Zo is not well controlled so there will be loss due to mismatch).
73
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Re: Fake NanoVNA? Or short between the headset :)
Remember when doing a new calibration, you FIRST must *clear* BEFORE
running the new calibration.
I can not imagine two units behaving identically in this respect.
Dave - W?LEV
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On Fri, Jul 8, 2022 at 10:07 PM <jetmech@...> wrote: I purchased a NanoVNA off of Amazon. Seem to work when I got it, but then
when I tried to calibrate it I'm able to. I even tried updating the
firmware. I exchanged it for another one and this time It will not
calibrate at all. I tried using the RF Demo kit as well. I got the -H, but
the RF Demo kit says its for the -F, did I kill the NanoVNA using the -F RF
Demo kit?
The replacement when using the smith chart doesn't move from center even
with open or shorted cap.
FWIW I know .001% of what I'm doing.
-- *Dave - W?LEV* *Just Let Darwin Work*
--
Dave - W?LEV
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Fake NanoVNA? Or short between the headset :)
I purchased a NanoVNA off of Amazon. Seem to work when I got it, but then when I tried to calibrate it I'm able to. I even tried updating the firmware. I exchanged it for another one and this time It will not calibrate at all. I tried using the RF Demo kit as well. I got the -H, but the RF Demo kit says its for the -F, did I kill the NanoVNA using the -F RF Demo kit?
The replacement when using the smith chart doesn't move from center even with open or shorted cap.
FWIW I know .001% of what I'm doing.
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Re: Common ground and 2-port measuring
Hello Ed, To measure the differential mode performance, the windings must be wired
in series and provide an anti-phase arrangement - that is winding 1 end is
joined to winding 2 end and nano VNA connections are channel 0 & channel 1
to winding 1 start and winding 2 start.
I have not seen this configuration before (I use the configuration mentioned here: ). Any link to an article about this way of measuring DM? All the best, Victor
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Re: Common ground and 2-port measuring
The diagram from Miro F9LR is very generalized.
It is not specific for the case where the DUT is a common mode current choke (current balun).
It might be helpful to review what a common mode choke is to establish how to correctly connect it to a nanoVNA.
A common mode choke is a transformer having two seperate, isolated windings, each having a start point and an endpoint. It is intended for use in a balanced transmission line.
The nanoVNA channels are 'unbalanced' and share a common (cold) connection.
The common mode choke has 4 wires or terminals, these must be connected correctly to configure it as the DUT. The wiring arrangement is different for measuring thru performance of the common mode signal and the differential mode signal.
The 4 wires, I will call winding 1 start, winding 1 end, winding 2 start and winding 2 end.
Now the common signal means that the same signal must be applied to both windings in the same orientation or polarity. Therefore winding 1 start must be connected to winding 2 start and winding 1 end connected to winding 2 end.
Respectively, the joined wires or terminals are connected to nanoVNA channel 0 and channel 1, to measure the common mode performance.
To measure the differential mode performance, the windings must be wired in series and provide an anti-phase arrangement - that is winding 1 end is joined to winding 2 end and nano VNA connections are channel 0 & channel 1 to winding 1 start and winding 2 start.
I hope that helps
Ed G8FAX
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Re: nanovna-saver/displayed charts/S11 R/¦Ø & X/¦Ø (?? / Hz)
Hello Francois, I made an error (this was highlighted to me by a fellow list reader): everywhere I use: mu' + jmu", should have been mu' - jmu" All the best, Victor Op di 5 jul. 2022 om 23:13 schreef Victor Reijs via groups.io <pe1atn.victor.reijs@...>:
Hello Francois,
Op di 5 jul. 2022 om 20:17 schreef F1AMM <18471@...>:
¦Ø for the pulsation and ¦Ø = 2.¦Ð.f
¦¸ for ohms
But you used R/¦¸ (in "S11 R/¦¸ & X/¦¸"), so I repeated that (did not want to
introduce something new), but indeed it is R/¦Ø
When it happens at home, I read
Now Z = C* ¦¸* ( mu'+j*mu")
I understand
Z = C¦Ø (mu'+jmu")
Correct.
You said
The C is depending on the physical layout of the toroid (and constant for
that toroid).
Ok but what is m ? why 'm' is not in C as
Z = K¦Ø (u'+ju") ??
mu is the greek letter ¦Ì (so not m*u;-)
You have write :
Z is measured by the nanoVNA. By dividing the Z by , you get a value that is:
Z' (=Z/ ¦¸ ) = C* ( mu'+j*mu") I supose
Z' = Z/ ¦Ø = C ( mu'+jmu")
Correct: Z' = Z/ ¦Ø = C ( ¦Ì '+j ¦Ì ")
Z is calculated by the nanoVNA thrue S11 i suppose
What do you do with Z'
Z' is also calculated by NanoVNA Saver (it is whe graph you did/do not
understand: Z/ ¦Ø ).
Do you plot Z' as a function of ¦Ø ?
Indeed, NanoVNA does that for you.
All the best,
Victor
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Re: NanoVNA Is it possibel to add RFI capability
Well.. you already see the multifunction capability (Spectrum Analyzer, 1 direction VNA) in popular instruments like the Keysight Fieldfox, and similar devices from Anritsu, etc.
There will always be a market for single purpose devices - highly cost (or size/weight/power) constrained applications where you don't want to spend the extra pennies for the components; and where you need the ultimate in measurement performance. It's like counters and spectrum analyzers - both can measure the frequency of a signal, but they tend to have different reference oscillators (ADEV vs Phase Noise optimization) and because they use different measurement techniques, they are optimized for particular applications. Another example might be precision measurement of RF power - a broadband calorimetric power meter or a narrow band filter with a detector (what a spectrum analyzer is). Getting 0.5% accuracy from a broadband power meter is straightforward, getting 0.1% uncertainty is difficult, but possible. I don't think there's a spectrum analyzer made that has that kind of accuracy. Typically, it's more like 0.2 or 0.5 dB (5% - 12%).
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Re: Common ground and 2-port measuring
Hello all of you, Op vr 8 jul. 2022 om 19:58 schreef DP <dpoinsett@...>:
For DC or low frequency AC, the return current path in this circuit is on
the bottom copper plane directly immediately between the two ports and
diffused widely over the rest of the bottom surface. As the signal
frequency is increased, the electrical and magnetic fields begin to
concentrate almost entirely in the small space between the top trace and
the bottom copper plane. At RF frequencies, the return current path on the
bottom plane is directly below the trace and NOT between the ports even if
they are close.
Perhaps this is related: When transporting non-DC currents in a coax, both the shield and the core need to be transporting the TE mode, and thus the coax has to be the return path and not the connection between the port-1 and port-2 of the NanoVNA. RF return current always flows via the path of least reactance. Here's
more info:
Nice article! Thanks, Victor
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Re: Common ground and 2-port measuring
"On the port 0 I connect shield and center conductor (as with any coaxial transmission line), on the other port I do the same. Simple connection, nothing fancy. Shield to shield, hot to hot :)"
"Now I have internally bonded ground between shields at Port 0 and Port 1, and i ALSO have shield of the coaxial cable connecting grounds of those two ports!!! THAT DOES NOT SEEM RIGHT!"
Hi Miro,
With a properly connected and calibrated S21 setup, the internal ground connection between ports in the Nano is not a problem. There is almost no RF current along that path, and calibration will account for the very very small amount that may exist. I know this seems counter-intuitive.
Imagine a large double-sided PCB. The bottom of the board is a solid copper plane. The top has a single copper trace that starts at one edge and takes a big U-shape path across the board and returns to a nearby edge. Inject RF at the starting edge between the top trace and bottom plane (call it Port 1) and terminate the end edge with a resistor between the trace and bottom plane (call this Port 2).
For DC or low frequency AC, the return current path in this circuit is on the bottom copper plane directly immediately between the two ports and diffused widely over the rest of the bottom surface. As the signal frequency is increased, the electrical and magnetic fields begin to concentrate almost entirely in the small space between the top trace and the bottom copper plane. At RF frequencies, the return current path on the bottom plane is directly below the trace and NOT between the ports even if they are close.
It's the same in the Nano. With typical coax connections between the ports and through the device under test, there is almost no RF current in the ground connection between the Nano ports. Almost all of the RF return current flows thought the port connector, coax shield, and DUT.
RF return current always flows via the path of least reactance. Here's more info:
Dave NU8A
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Arie Kleingeld PA3A
Douglas Butler
Roger Need
Clyde Lambert
