Built a 110uH air coil for my EFHW from a calculator. Chucked it on my NanoVNA as described and ended up at 110.6uH. Close enough for me. Thanks for the guide
Thanks very useful. Just a suggestion, if you display the S11 return loss, then at the resonant point you get the deep dip and its easier and less subjective as to where to position the marker to read off the frequency.
Thanks for this video. Please also consider that such a capacitor may vary up to 20% from its marked value, a typical tolerance for low cost capacitors. So the calculated value of inductance may also vary within that margin of error
Ultimately you need an accurate value for the capacitor. It's not just manufacturing tolerance but also the characteristics changing with increasing frequency - particularly with poorer quality capacitors. This test gives a ball park figure (or a bit better) and I think that was all he was looking for - it's good enough for what he wanted.
You didn't mention it, but you should do a calibration with the cable and adaptor you are using first. But here is another issue: the permeability of the toroid material varies with frequency. So you have measured the inductance at 37 MHz, which is not where it will be used in the QCX! To use your method, you should select a larger capacitor in order to get the resonant frequency closer to the operating frequency.
I approached the measurement as if I didn't have any idea of what the inductance might be. Then I confirmed the measured result with an LCR meter. The LCR meter uses a frequency of 100 kHz to make these measurements - that's a long way from 37 MHz and yet both methods indicated 0.9 uH for the coil.
@@AE5X It may depend on the particular toroid material. I am going to do some experiments. I have an LCR meter (several), an MFJ antenna analyzer, a GDO, and a NanoVNA, and I will compare the results at several frequencies.
@@4X6GP - I think I'll do the same. The reason for identical results at greatly different frequencies is probably due to the broadbanded nature of the toroid core's permeability. Ideally, several core types and measurement methods would be compared...not sure how many types I have on hand though.
Really useful thanks! It would have be good to see how the Nano compared with your dedicated LCR meter but I see from the comment below, it was the same. Good work!
Sweet. I am about to build a receiver & all my testers for L & C had crapped out when fired up. I do have a working Nano Vna & of course it came without any manual but I figured it could do the job but how. Now we know. Another guy read L directly but he did not share where in the vna's menu settings he was. This on the other hand is a simple indirect means to get what is needed. I even sent away for a $20 tester today. Well, it does not hurt having back up....
The underlying formula is f = 1/(2π*(L*C)^(1/2)), where f = frequency, L = inductance, C = capacitance. Please mind, that the values are given in Hz, H, and F. So you must adjust for M, µ and p.
Rearranged for the unknown value of L and corrected for scientific notation, the Excel (or Google Sheets) formula is "=(((1/(6.28*K24))^2)/K25)*10^6" where K24 is the frequency in MHz and K25 is the capacitor value in pF. The 10^6 converts Henries into uH. (For those unfamiliar with formulas, the K is the column and the 24 and 25 are the rows.)
@@W1RMD I've got the 2.8" and I like that it fits in a tiny pocket of my go-bag for portable antenna work. In the house or shop, I hook it up to a PC so the screen size doesn't matter.
@@socallars3748 Good to know. I believe that this also can be updated from 101 to 401 points with the proper software as well. Other than the screen being a little hard to see, it seems like a great product for the price.
@@W1RMD It really is a great value, I can't see paying several hundred dollars for a RigExpert or the like when these cheap little things works so great and do so much more. It is a bit hard to see in bright sunlight, but the only thing I'm typically doing outdoors is quick SWR checks and it's manageable. If mine broke, I'd buy another tomorrow.
The measurement adapter should be mounted on the SMA socket and not at the end of the cable. Calibration of SOL (Short, Open, Load) must be done on the adapter. Use two 100 Ohm SMD resistors with 1% tolerance (in parallel) as LOAD. After calibration, OPEN measurement and delay compensation (Phase equal to ZERO degrees) But this calibration is not 100% accurate anyway.
No it is not 100% accurate. I've made these measurements a number of times using various calibration methods, with very little difference in the value obtained for the measured device.
Tried this with different inductors and the all ended up ~3uH +/- 0.2, even if i removed the inductors and measured just the capacitor. That can't be true, one of the inductors was wire coil, and other two were different torroids. What I suspect, I measured is the phase shift on "antenna" which was made up by the wires leading up to LC circuit. Also - phase shifts multiple times across broad frequency range, which one do we use for calculation?
Built a 110uH air coil for my EFHW from a calculator. Chucked it on my NanoVNA as described and ended up at 110.6uH. Close enough for me. Thanks for the guide
Thanks very useful. Just a suggestion, if you display the S11 return loss, then at the resonant point you get the deep dip and its easier and less subjective as to where to position the marker to read off the frequency.
Thanks for this video. Please also consider that such a capacitor may vary up to 20% from its marked value, a typical tolerance for low cost capacitors. So the calculated value of inductance may also vary within that margin of error
Ultimately you need an accurate value for the capacitor. It's not just manufacturing tolerance but also the characteristics changing with increasing frequency - particularly with poorer quality capacitors.
This test gives a ball park figure (or a bit better) and I think that was all he was looking for - it's good enough for what he wanted.
You didn't mention it, but you should do a calibration with the cable and adaptor you are using first. But here is another issue: the permeability of the toroid material varies with frequency. So you have measured the inductance at 37 MHz, which is not where it will be used in the QCX! To use your method, you should select a larger capacitor in order to get the resonant frequency closer to the operating frequency.
I approached the measurement as if I didn't have any idea of what the inductance might be. Then I confirmed the measured result with an LCR meter. The LCR meter uses a frequency of 100 kHz to make these measurements - that's a long way from 37 MHz and yet both methods indicated 0.9 uH for the coil.
@@AE5X It may depend on the particular toroid material. I am going to do some experiments. I have an LCR meter (several), an MFJ antenna analyzer, a GDO, and a NanoVNA, and I will compare the results at several frequencies.
@@4X6GP - I think I'll do the same. The reason for identical results at greatly different frequencies is probably due to the broadbanded nature of the toroid core's permeability. Ideally, several core types and measurement methods would be compared...not sure how many types I have on hand though.
Measured my homebrew inductor coils directly with nanovna. Matched calculated. S11, in series.
Edit: antenna loading coils. Large inductors. 5" × 9".
Really useful thanks! It would have be good to see how the Nano compared with your dedicated LCR meter but I see from the comment below, it was the same. Good work!
Good job! I have to try and compare results with digital capacitance&inductance meter.
Sweet.
I am about to build a receiver & all my testers for L & C had crapped out when fired up.
I do have a working Nano Vna & of course it came without any manual but I figured it could do the job but how. Now we know.
Another guy read L directly but he did not share where in the vna's menu settings he was. This on the other hand is a simple indirect means to get what is needed.
I even sent away for a $20 tester today. Well, it does not hurt having back up....
The underlying formula is f = 1/(2π*(L*C)^(1/2)), where f = frequency, L = inductance, C = capacitance. Please mind, that the values are given in Hz, H, and F. So you must adjust for M, µ and p.
Rearranged for the unknown value of L and corrected for scientific notation, the Excel (or Google Sheets) formula is "=(((1/(6.28*K24))^2)/K25)*10^6" where K24 is the frequency in MHz and K25 is the capacitor value in pF. The 10^6 converts Henries into uH. (For those unfamiliar with formulas, the K is the column and the 24 and 25 are the rows.)
aren't you adding the unknown frequency responses of another component now, and kind of doubling the size of the problem?
No, I'm not. I'm adding the known frequency response based on the capacitor's labeled value.
Thanks for the information 👍
Great video! Thanks for showing. Is that VNA the H 2.8 inch screen or H4 with the 4" screen?
That's the 2.8" in the video but I now have the H4.
Is the H4 much better outside of the screen size?@@AE5X
@@W1RMD I've got the 2.8" and I like that it fits in a tiny pocket of my go-bag for portable antenna work. In the house or shop, I hook it up to a PC so the screen size doesn't matter.
@@socallars3748 Good to know. I believe that this also can be updated from 101 to 401 points with the proper software as well. Other than the screen being a little hard to see, it seems like a great product for the price.
@@W1RMD It really is a great value, I can't see paying several hundred dollars for a RigExpert or the like when these cheap little things works so great and do so much more. It is a bit hard to see in bright sunlight, but the only thing I'm typically doing outdoors is quick SWR checks and it's manageable. If mine broke, I'd buy another tomorrow.
How is the terminal strip connect to the SMA connector. Are the centre and shield both connected?
Yes, they are.
What value did you get with your LCR meter? Also did you get the QCX on the air?
I got the same value with the meter. My QCX is receiving but not transmitting yet :-(
Can we sweep from 1khz to higher value. Basically I want to know. We are able to sweep from low frequency or not. Because i want to buy
mine start at 50khz.. i think that this starting point is common!
The measurement adapter should be mounted on the SMA socket and not at the end of the cable. Calibration of SOL (Short, Open, Load) must be done on the adapter. Use two 100 Ohm SMD resistors with 1% tolerance (in parallel) as LOAD. After calibration, OPEN measurement and delay compensation (Phase equal to ZERO degrees) But this calibration is not 100% accurate anyway.
No it is not 100% accurate. I've made these measurements a number of times using various calibration methods, with very little difference in the value obtained for the measured device.
if you calibrate out to the end of the cable, the cable is ignored!
Tried this with different inductors and the all ended up ~3uH +/- 0.2, even if i removed the inductors and measured just the capacitor. That can't be true, one of the inductors was wire coil, and other two were different torroids. What I suspect, I measured is the phase shift on "antenna" which was made up by the wires leading up to LC circuit. Also - phase shifts multiple times across broad frequency range, which one do we use for calculation?
I got similar results when the cable from the VNA port to the DUT was too long. It's supposed to be as short as possible.
can’t to use the excel file less to pay for it on windows 7.. but yes, it’s a helpful way to find the value.. thanks!!
Google Sheets is freeish.