开云体育

Hey guys,

I have NO affiliation with this company but Battery Hookup has absolutely the best prices when it comes to the 18650 lipo cells. They also have flat cells with power levels of 4.5Ahr @ 3.7v

Mike C. Sand Mtn GA

On Sun, Jun 25, 2023 at 03:15 PM, Roger Need wrote:

The VNA can only measure R + jX or R//jX (with later firmware versions). It
calculates inductance by dividing X by 2*pi*frequency and this ONLY gives an
estimate of the true coil L if the coil is air wound and the frequency is low
enough that the skin effect is not having much effect on underlying
inductance.

Roger, the method I suggested requires inductance calculated this way. It yields an accurate coil model over a narrow frequency range. To my surprise, it seemed good enough over the whole 3.5-4 MHz band. But the wideband model suggested in the writeup noticeably improved accuracy over the somewhat wider 88-108 MHz band.

Brian

On Sun, Jun 25, 2023 at 11:04 PM, Roger Need wrote:

On Sun, Jun 25, 2023 at 02:27 PM, Mike wrote:

Thank you Roger. The coil is 95 turns of 0.9mm enamelled copper wire close
wound on a 36mm PVC former.

Mike,

Attached is an analysis of your coil using Coil64. The numbers are close to
what you measured. For an air wound coil the actual L will not vary much in
the frequency range of up to 12 MHz. Note the following:

--> ESR is increasing with frequency and simulation shows .299 ohms at DC,
.422 at 1 MHz. and 9.233 ohms at 5 MHz.
--> Self capacitance is calculated at 1.61 pF which is very small. You
estimated 2 pF based on your SRF measurement. Any stray capacitance in your
test setup will significantly affect your self resonant frequency so you need
a good test jig if this is an area of concern.

Note: For air wound coils assuming that apparent inductance at low frequencies
is equal to actual inductance L at higher frequencies is a reasonable
approximation. Therefore the method of calculating parasitic capacitance
based on using this value of L and the SRF to calculate parasitic capacitance
gives a decent estimate. BUT this method does not work if the inductor is a
ferrite core design.

Roger

Perfect! Thanks for that explanation Roger.

--
Mike

On Sun, Jun 25, 2023 at 02:55 PM, Brian Beezley wrote:

Mike, measure the inductance and series resistance at the model frequency. I
believe recent VNA firmware versions can provide these values directly.
Otherwise calculate them from R and X.

The VNA can only measure R + jX or R//jX (with later firmware versions). It calculates inductance by dividing X by 2*pi*frequency and this ONLY gives an estimate of the true coil L if the coil is air wound and the frequency is low enough that the skin effect is not having much effect on underlying inductance. If the coil is wound on a ferrite core you can't use this method to estimate L at higher frequencies.

Roger

On Sun, Jun 25, 2023 at 02:27 PM, Mike wrote:

Thank you Roger. The coil is 95 turns of 0.9mm enamelled copper wire close
wound on a 36mm PVC former.

Mike,

Attached is an analysis of your coil using Coil64. The numbers are close to what you measured. For an air wound coil the actual L will not vary much in the frequency range of up to 12 MHz. Note the following:

--> ESR is increasing with frequency and simulation shows .299 ohms at DC, .422 at 1 MHz. and 9.233 ohms at 5 MHz.
--> Self capacitance is calculated at 1.61 pF which is very small. You estimated 2 pF based on your SRF measurement. Any stray capacitance in your test setup will significantly affect your self resonant frequency so you need a good test jig if this is an area of concern.

Note: For air wound coils assuming that apparent inductance at low frequencies is equal to actual inductance L at higher frequencies is a reasonable approximation. Therefore the method of calculating parasitic capacitance based on using this value of L and the SRF to calculate parasitic capacitance gives a decent estimate. BUT this method does not work if the inductor is a ferrite core design.

Roger

On Sun, Jun 25, 2023 at 10:55 PM, Brian Beezley wrote:

Mike, measure the inductance and series resistance at the model frequency. I
believe recent VNA firmware versions can provide these values directly.
Otherwise calculate them from R and X. Then create a simple load with the
inductance and resistance in series. This works fine over a single ham band.
To create a wideband model, see this:



Brian

Thanks for the link Brian.

--
Mike

Mike, measure the inductance and series resistance at the model frequency. I believe recent VNA firmware versions can provide these values directly. Otherwise calculate them from R and X. Then create a simple load with the inductance and resistance in series. This works fine over a single ham band. To create a wideband model, see this:



Brian

On Sun, Jun 25, 2023 at 10:25 PM, Jim Lux wrote:

ESR is the ohmic resistance *at RF* which will be higher than the DC
resistance (skin effect).

What you should be able to do is measure the Z (both X and R) far away
from self resonance, and get a rough estimate.

Thank you Jim.

--
Mike

Thank you Roger. The coil is 95 turns of 0.9mm enamelled copper wire close wound on a 36mm PVC former.

--
Mike

On 6/25/23 1:26 PM, Mike wrote:

I have wound a 110uH coil for an antenna system and I want to create a model of the inductor that I can use in a simulation program. In other words, I need to know the inductance, parasitic capacitance and ESR.
Using my NanoVNA-H4 I measured the inductance on a Smith chart at a low frequency (around 70kHz) where the reactance is about 50 ohms. I then measured the self resonant frequency (10.5MHz) and calculated the parasitic capacitance as 2pF.
Is that correct so far?
What about ESR? Is that the ohmic resistance of the coil or is it more complicated than that?
Thanks!

ESR is the ohmic resistance *at RF* which will be higher than the DC resistance (skin effect).

What you should be able to do is measure the Z (both X and R) far away from self resonance, and get a rough estimate.

On Sun, Jun 25, 2023 at 01:26 PM, Mike wrote:

I have wound a 110uH coil for an antenna system and I want to create a model
of the inductor that I can use in a simulation program. In other words, I need
to know the inductance, parasitic capacitance and ESR.

Using my NanoVNA-H4 I measured the inductance on a Smith chart at a low
frequency (around 70kHz) where the reactance is about 50 ohms. I then measured
the self resonant frequency (10.5MHz) and calculated the parasitic capacitance
as 2pF.

Is that correct so far?

What about ESR? Is that the ohmic resistance of the coil or is it more
complicated than that?

Yes it is more complicated than that. The inductance will vary with frequency and so will the ESR. In the case of an air wound coil the underlying inductance will slightly change as you increase frequency due to the "skin effect" which forces current to the outer perimeter of the conductor. If the coil is wound on a powdered iron or ferrite core there will be considerable change of inductance with frequency due to the permeability decreasing with frequency. The ESR will increase with frequency due to core losses and the skin effect which increases the RF resistance of the coil windings.

When you try to measure the inductance of an inductor using a VNA the firmware or PC application will calculate the "apparent inductance" by simpling dividing the measured reactance by 2*pi*frequency. This is not the same as the actual inductance L. The reason is that the parasitic capacitance is in parallel with the inductor and you now have capacitor reactance in parallel with the inductor reactance which results in a higher reactance than that of the inductor alone. This is shown in the attached diagram.

So if you tell us what type of inductor you are measuring (air wound, powdered iron or ferrite) more specific information can be provided.

Roger

On rf the resistance is higher as dc resistance
Dg9bfc sigi

Am 25.06.2023 22:26 schrieb Mike <mail@...>:

I have wound a 110uH coil for an antenna system and I want to create a model of the inductor that I can use in a simulation program. In other words, I need to know the inductance, parasitic capacitance and ESR.

Using my NanoVNA-H4 I measured the inductance on a Smith chart at a low frequency (around 70kHz) where the reactance is about 50 ohms. I then measured the self resonant frequency (10.5MHz) and calculated the parasitic capacitance as 2pF.

Is that correct so far?

What about ESR? Is that the ohmic resistance of the coil or is it more complicated than that?

Thanks!
--
Mike

Hi. Few questions:
1) I organized the name format of the .cal files stored in the microSD card of my NanoVNA-H4 as per the image in order to easily find them, as only capital letters can be used and dots / commas aren't available. How about you?
2 ) Have you tried to rename them with the PC in order to also use the lower case letters, commas, etc. (e g. 1.8MHz-29.7MHz.cal)? Did you get issues?
Many thanks.

Thanks for all the help
I do have the smaller original VNA-H model
It does have a rechargeable battery. I charged it up and the unit turns on and there is software in it.
I'll purchase some SMA adapters to able to connect it to antennas.

I was watching videos on the wrong models and got confused.

i have an extra battery from a smashed screen unit kicking around i could
drop it in an envelope for you if you like

'Way back when the nanovna was new (about 4 years ago, I think), the cheapest ones came without battery - but mainly due to shipping restrictions in the originating country (hazardous material).

Did you look to see if there is a battery inside? The cheapest ones (like I bought then) do not have a case. You can see the circuit boards in it.

Plug yours into a USB connector or charger to give it power, and then see if it works.
--
Doug, K8RFT

If it's a real -H, it should already have a rechargeable battery inside the
case, and you charge it with a USB cable.

On 6/24/23 2:42 PM, Michael wrote:

I bought one of these. I got the most inexpensive one. It says on the back
it is a VNA-H, it just covers the HF frequencies. I thought it would come
setup and ready to use.
Oops!
I thought it had a rechargeable battery, but doesn't look like it does.
So correct me if I'm wrong.
1 I need a battery pack to run it. 5 volts?

No, probably a standard 13650 battery - 3.5 volts.

2 I need a SD card of 32 gigs.

Nope, not unless you want to save data and move it somewhere else.

3 I have to download the software for it.

Only if you want to upgrade the existing firmware or use it with a PC. Mine's 2-3 years old, and I'm running the original firmware.

4. Then I can figure out how to use it with online documentation.

Yes, and copious questions here.

Are these the correct steps? It is possible to get a card with the firmware
installed on it? I ask because I don’t really have a good computer right
now, but I think I could probably borrow a laptop from the time it would
take to install it.

You don't load software from the SD card - that's just to store measurements. If you want to upgrade the firmware, you'd do that from a PC.

So will these head me in the correct direction ?
Mike
KB1IUI

I bought one of these. I got the most inexpensive one. It says on the back
it is a VNA-H, it just covers the HF frequencies. I thought it would come
setup and ready to use.
Oops!
I thought it had a rechargeable battery, but doesn't look like it does.

So correct me if I'm wrong.
1 I need a battery pack to run it. 5 volts?
2 I need a SD card of 32 gigs.
3 I have to download the software for it.
4. Then I can figure out how to use it with online documentation.

Are these the correct steps? It is possible to get a card with the firmware
installed on it? I ask because I don’t really have a good computer right
now, but I think I could probably borrow a laptop from the time it would
take to install it.

So will these head me in the correct direction ?
Mike
KB1IUI