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Adding to my reply:

The reactance of 470nH at 50kHz is barely 0.15?. You cannot expect the NanoVNA to measure that accurately. You need at least 5MHz or so to bring the reactance up into a range where the NanoVNA is pretty accurate. A small SMD inductor like that one shouldn't have much parasitic capacitance effects yet at that frequency. 5MHz is "low frequency" in this case.

SMD inductors typically have pretty low Q. You need to make sure that you are not mixing up resistance with reactance. Use the RLC function.

Also SMD inductors typically have ±20% tolerance, so that can explain at least a part of the discrepancy you see.

Ed,

What I am trying to
understand is how one relates the marked value of a component to what nanovna
shows.

The value marked on a component is supposed to be valid at a very low frequency. As soon as the frequency goes up, parasitic effects become increasingly important, so the actual value of the part varies with frequency. Also, of course, there is always a tolerance. With good capacitors and air-core inductors this tolerance might be only 5%, but with ferrite-cored inductors it can easily be 40%, and with some sorts of ceramic capacitors it can be even larger.

So, rule #1 is to measure on the lowest frequency possible, and rule #2 is to never forget that the marked value is subject to a tolerance.

But then the characteristics of the measuring instrument come into play. The NanoVNA is natively a 50? instrument. It should produce the best accuracy when measuring impedances reasonably close to 50?. When the impedance gets close to zero, or into the kiloohm range, the accuracy of the NanoVNA drops. So, if you are measuring small values of capacitance or inductance, measuring at the lowest frequency the NanovNA supports might produce poor measurement accuracy.

So, rule #3 is to measure at a frequency where the impedance of your part is at least close to the order of magnitude of 50?.

In practice that means that you should look at what frequency the part has a reactance of 50?, and then measure at a frequency a few times lower. If the measured value is reasonably constant over the range between those two frequencies, then probably you have a valid measurement. If instead it varies all over the place, it probably means that there are too high parasitics even in that frequency range.

Of course I'm assuming that you properly calibrated the NanoVNA, putting the short and the load exactly at the same place where you then put the part to be measured.

In my experience it's best to use the shortest possible connection between the NanoVNA and the part under test. It seems that correct measurement of difficult impedances through a long piece of coax cable is harder for the NanoVNA, even when carefully calibrated through that long cable.

Always keep in mind that if you do all this and get a consistent result, then you are getting the low frequency value of the part you are testing, and that at higher frequency its actual value will change. At a high enough frequency a capacitor becomes a short circuit, further up it becomes an inductor. And what's an inductor at low frequency will become an open circuit at some high frequency, and a capacitor beyond that. Generally both inductors and capacitors will rise in value, when you start going up in frequency starting from a low frequency. But core materials tend to decrease their permeability beyond some frequency, and this effect can win over the other in some cases, so you might see cored inductors whose value goes down rather than up, when increasing the frequency. These are all real effects, not measurement errors! In RF work you often need to measure each part at the frequency you will be using it, rather than trusting the value printed on it, which is valid only at low frequencies.

On Sat, Feb 13, 2021 at 07:48 PM, Cierra wrote:

use a nanoVNA to test a transmitter

To over simplify a bit, the nanovna is a transmitter. It also has a sensitive meter circuit inside, which would probably be destroyed by power from an external transmitter such as your kit. A poor, rough comparison would be like using an ohmmeter to check your house power wiring while the power is still on.

But you CAN use it to check parts and circuits inside the transmitter while the the transmitter is not turned on (not connected to a power supply of any sort). Is that what you meant?

--
Doug, K8RFT

The short answer is NO you still need a dummy load or an attenuator that can handle the power from the transmitter. Then VNAs are not really designed to do spectral analysis of transmitter output. VNAs measure the characteristics of antennas, filters, and with the correct attenuator, amplifiers. They need to control the source frequency being used to measure the characteristic. A Spectrum Analyzer (SA) can measure the output of a transmitter for signal characteristics by scanning the frequencies that the receiver in the SA measures. An inexpensive SA would be the TinySA.

So a VNA is measuring the network being tested by adjusting the stimulus feeding the network and measuring the result. A spectrum analyzer scans the frequencies in question and measures what it sees regardless of what the device is sending.

Both have limits on how much power can be applied to the input before overload and damage occurs. That is why you need a dummy load and/or the proper attenuator.

You can look up NanoVNA and TinySA on the internet to find out more about these instruments.

73
Evan
AC9TU

This might be a dumb question, but I wanted to know if you can use a nanoVNA to test a transmitter built from a PCB kit (like instead of a dummy load). I realize VNAs are usually used for antenna applications, but I was just curious.

Hello Ed,

Curious, if you go to item13 on your card, take that reading at 50 kHz and SUBTRACT the L value from the reading at 50 kHz done at item8... Do you get 470 nH? A reading of 700 nH at 50 kHz points to a serious cal issue or a fixture parasitic that is begging to be removed as well understood.

I suspect that your L is not that far off or out of tolerance by nearly 100 %.

Alan

HI,
I use a different approach when I need to know the exact value of inductance or capacitance, I build up a simple jig on a PCB mount connector with a series 50 ohm chip resistor then put the component in series to ground.? With the standard Xc or Xl formula determine the frequency where the value is between 25 to 100 ohms.? I use 1 or 10 MHz and using the formula in reverse extract the true value of the component.? Works very well.? It tells you the net value with all parasitic errors normalize in. So that the VNA reads Z50+/-j.
Mel, K6KBE

Not exactly like this, but see:

and

On 2/13/21 6:39 AM, Ed Krome wrote:

Thank you for the responses. I think I was unclear. What I am trying to understand is how one relates the marked value of a component to what nanovna shows. Using DL5FA’s item 8 inductor, my devices show 700 nH @50khz. But at 100mhz, the reading is 1uH. But the component is speced as 470nH, a value I can’t see anywhere, regardless fir frequency. How should I be reading this thing?
Thanks!

There is always some parasitic C around, which usually "reduces" (or cancels) some of the inductance - sort of the opposite of what you're seeing - but in any case, the amount of cancellation you get is frequency dependent (since the VNA is measuring X, and then converting that to nH)

Are you allowing for the inductance of the leads going to the component.? A handy thing is "about 1 nH/mm or 1 uH/meter" for a single wire.

Alan, thank you - that fixed the issue!

Dave

Does anyone know of an SMA equivalent to this board? I expect it would be an order of magnitude more expensive, but u.fl connectors are only expected to live through <10 insertion/removal cycles. I am thinking about creating such a board. If I do, I'll make the Gerbers available here.

Brent, AB1LF

Thank you for the responses. I think I was unclear. What I am trying to understand is how one relates the marked value of a component to what nanovna shows. Using DL5FA’s item 8 inductor, my devices show 700 nH @50khz. But at 100mhz, the reading is 1uH. But the component is speced as 470nH, a value I can’t see anywhere, regardless fir frequency. How should I be reading this thing?
Thanks!
--
Ed K9EK

From: "Bob Albert via groups.io" <bob91343@...>
Date: February 12, 2021 at 6:36:54 PM PST
To: [email protected]
Subject: Re: [nanovna-users] measuring Capacitance or Inductance
Reply-To: [email protected]

? The inductance will change with frequency. I use the Smith chart and the resistance and inductance are displayed at the marker frequency.
Bob

The inductance won’t change with frequency (to a first order approximation and especially over a somewhat narrow range).

What will change is the reactance with respect to frequency.

XL= 2*pi*F*L
XC= 1/(2*pi*F*C)

The L and C values shown by the marker is calculated by solving for those values at a specific frequency (where the marker is set to)

Ray WB6TPU

Roger, Thanks for the suggestions. I have updated the firmware in my nanoVNA to v1.0.45 and everything is working fine now.
I would like to try the new NanoVNA app (Windows) by OneOfEleven, but I'm having trouble locating the Win 64 installation file.
I would appreciate it you could send me the link. Thanks, Geoff

The inductance will change with frequency.? I use the Smith chart and the resistance and inductance are displayed at the marker frequency.
Bob

Concerning how to measure capacitance and inductance on the RF Demo board (or any capacitor or inductor), reference /g/nanovna-users/wiki/16592. I can get the curves shown in this demo just fine.. but how to read the actual values off of those curves eludes me. On the item 8 inductor example, if I vary the frequency, I can make that component read about any value I want. I must be missing something. Help, please.
--
Ed K9EK

On Fri, Feb 12, 2021 at 01:05 PM, gmendenh1947 wrote:

Roger, I wanted to try the new features in v 0.8.0-20200620 released on Jun
19, 2020 by edy555 including the contributions of DiSlord.
I posted looking for a solution and if it is a bug, I wanted to let edy555
know about it.

I can always revert back to v 0.2.3-2, Oct 18, 2019 if necessary unless you
can suggest a newer, bug free version.

Why not try the latest version by DisLord (1.0.45) in the files section of this group. Some nice enhancements and it works with the new NanoVNA app (Windows) by OneOfEleven which has more features than NanoVNA Saver.

Roger

Sweeping normally. This is not the problem

Roger, I wanted to try the new features in v 0.8.0-20200620 released on Jun 19, 2020 by edy555 including the contributions of DiSlord.
I posted looking for a solution and if it is a bug, I wanted to let edy555 know about it.

I can always revert back to v 0.2.3-2, Oct 18, 2019 if necessary unless you can suggest a newer, bug free version.

Thanks,
Geoff

Hello Frank,

I do not have a BOM, but some documentation:
/g/nanovna-users/wiki/16592

73, Rudi DL5FA