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And since it's sunday and I have time for playing with the NanoVNA, I made measurements to show all of you the effect of placing bypass caps of different value in parallel. Attached are the impedance plots for 100nF alone, 1nF alone, and both in parallel. Whoa! Which option would you prefer?

Note that the 100nF cap alone provides a bypassing impedance below 3? from about 700kHz to about 70MHz. that's pretty good, I would say. The 1nF is bad on low frequencies, and the parallel combination is a total disaster! Yet that's what you will find in equipment designed by people who have never thought about this point, and are just following intuition, which often is wrong...

Dave,

We warmed up the HP impedance meter of the time (the one that had a
tunable drum as a frequency indicator and topped out at 110 MHz). Sure
enough, *EVERY* CK05 capacitor went purely resistive between 1.4 and 1.6
MHz and inductive above that.

What lead length did you use for that test?????

After my last post I grabbed my box of 100nF capacitors, fired up the NanoVNA (works well even without warming up!), and measured two dozen of them, with lead lengths typical for PCB mounting. Their resonant frequencies all fell in the range of 6 to 8.4MHz. As was to be expected, the smallest ones (leaded ceramic chips) had the highest resonance, and the largest foil capacitors had the lowest, inside that range.

I then measured with full length wires. My longest-legged one resonated at 1.85MHz. That one has 35mm long legs (each), of strongly magnetic material, which probably contributes to add lead inductance.

To get those low resonant frequencies, you must have had very long-legged capacitors, like 5cm, and you must have measured them with full lead lengths. Of course nobody would mount a bypass cap with full-length leads! So what you were getting on those boards must have been much better. Resonating around 7MHz, and producing acceptable bypassing to 30MHz or so, depending on the impedance requirements. In a great many situations that's good enough, specially with older electronics.

It has been stated, by multiple members of this group, that due to hardware
deficiencies (port 2 is not a perfect 50Ω) and lack of 12 term error
correction,
the "S21 method" can't be used to measure high impedance reliably.
I decided to test that and see how inaccurate is it really.

On the first graph the red and green traces are the measured values (R&Z)
and the blue and black traces are a simulation of a 10K resistor with 50fF
of parasitic
capacitance (figure from some Vishay paper).

[image: image.png]

The DUT is a resistor of unknown origin from China that measures (at DC)
9.995K ± 10Ω.
The VNA (Nano-H4) was calibrated using the DIY "standards", no compensation
of the test
jig during calibration, offset delay of -4.5ps was used during measurement.
Test jig was made from cheap SMA connectors from AliExpress, cables (RG405)
also.

[image: 2021-02-14 19.56.05.jpg]

Draw your own conclusions.

Clyde,

CAPACITANCE AND INDUCTANCE ARE SPECIFIED AT A GIVEN FREQUENCY. See the
example.

Yes, often the datasheet states the measurement frequency. But this is invariably a "low" frequency, low enough to keep parasitic effects negligible. The inductance or capacitance of a component won't vary significantly from that frequency down to DC.

The part value starts changing significantly at frequencies high enough to make parasitic effects significant.


Alan,

I have carefully measured normal HF range inductors with a dip oscillator and SDR at working frequencies comparing with a meter that measures
in the 100Khz range. I noticed no significant difference.

When the inductors are built in such a way that in the HF range the parasitics are low, then this is indeed the normal situation. But if you measure them at VHF, the values will very likely change. And at UHF they surely will. It's a simple matter of going high enough in frequency, to make the values of any part change dramatically.

At HF you can often get away with taking the low-frequency values and assuming they will hold true at your working frequency, But not always. And at VHF that becomes rarer, and at UHF it becomes very rare.


Dave:

Since I enjoy challenging you, I will do it again! ;-)

Now, ask yourself: "is an inductor good at bypassing rail noise
as the capacitor was intended to accomplish?" NO!

Well, it depends! A DC-blocked inductor can be a pretty good bypass element, no worse than a capacitor! It just depends on its impedance at the frequency in question. Such a "nasty" 100nF bypass capacitor is resonant at 1.5MHz when its equivalent series inductance is 112nH. A foil-wound capacitor might indeed be that bad. A ceramic capacitor only if mounted with very long leads. Anyway, assuming it has indeed 112nH and thus is resonant at 1.5MHz, how would it behave at 3MHz? Well, it would have a reactance of less than 2?! That's still a pretty good bypass, despite being inductive. At 100MHz it would be bad.

If you replace that nasty 100nF capacitor by a 10nF one, would it be better? NO, if you keep those long leads! It will be much worse bypassing low frequencies, it will be good at its resonant frequency near 5MHz, but at 100MHz it will be almost as bad as the 100nF one.

And what happens if you follow that old rule of putting the 100nF capacitor in parallel with a 1nF one? Well, at some frequency you get a might parallel resonant circuit, with the 100nF capacitor acting as the inductor, and at that frequency you get infinite impedance, and thus NO bypassing! Of course, only if the capacitors have high Q at that frequency. So the important point with bypass capacitors is: They should have enough capacitance for the low frequencies, low enough ESL for the high frequencies, and they should be bad! I mean, they should have a low Q. A high loss factor. That largely pevents getting unbypassed frequencies due to bypass caps happily parallel-resonating with each other.

There is a long-standing myth about electrolytic caps needing a parallel-connected ceramic cap to provide bypassing over a wide frequency range. Using a parallel ceramic cap is indeed useful if this is a chip capacitor. But placing something like a an old-fashioned disc ceramic cap in parallel with an electrolytic of comparable path length doesn't help much, since both have roughly the same ESL.

In some equipment I often see real collections of 6 or more different capacitors in parallel, placed there by some designer who thinks that each frequency will then take the path it likes best. The only problem is that physics don't work like that. Those nice showcases of six different capacitors in parallel are mainly good for one thing: Getting a good laugh!

I also often laugh about that old rule of "one bypass cap per IC". When using slow ICs, often a single bypass cap is enough for the entire board, and in other cases one cap every so much distance is enough. One can save quite a bit of money in series production by leaving out unnecessary parts. Of course without overdoing that...

On Fri, Feb 12, 2021 at 07:25 PM, gmendenh1947 wrote:

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

This is the only publicly available version I have found. Works on my Win 64 computer...
You want to download the .rar file and decompress it with something like 7 zip...

Thank you to all who replied. But, since the values I was seeing didn't match prescribed values (and it was driving me a bit nuts), I tried the experimental approach. I took a single RF Demo Kit board with the same cable. I carefully calibrated my 3 nanoVNA's (nanoVNA 2.8", nanoVNA H4, nanoVNA SAA-2N), each 50kHz to 300MHz. Then I recorded the values of the components at position 7 (capacitor) and posn. 8 (inductor) at increments over the frequency range. Results showed remarkably good correlation over reduced frequency range on all three nano's. Pos. 7 showed the capacitor to be 100pF from 0.1 to 100 MHz. Posn 8 showed the inductor to be 700nH from 0.1 to 30 MHz. Things went rapidly askew at higher frequencies, although trends were similar. The capacitor lines followed each other reasonably well all the way to 300 MHz on all 3 nano's, but the inductor curves, while trending similarly, showed marked differences in values between the 3 different nano's. As a reality check, I measured the inductor on an AADE L/C meter IIB and read 700nH. This wasn't as precise a setup as with the nano's. Curves attached
I think I'm getting a handle on this now. Thanks again.

Ed K9EK

Excellent presentation thanks for sharing! :-)

73!
Greg / W4GAP

I once loaned a (VERY CHEAP) analog multimeter to some technicians that used it to check the resistance of the power lines. When they brought it back, the inside of the case was copper clad.. They reimbursed me for my $3 multimeter.
Ed

I say go for it, 1.2W is nothing and the soldering lesson you will get
afterwards
will be a great learning experience.

On Fri, Feb 12, 2021 at 06:33 PM, Ed Krome wrote:

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,

There have been a number of good posts by others describing the characteristics of inductors and capacitors versus frequency. Parasitic capacitance is a big factor and needs consideration.

This post will hopefully be a direct answer to your question of how to read the inductance value on the NanoVNA.

The first step is to make sure that you have calibrated correctly using the open, short and load that are on the test board. This is cumbersome because those little u.fl connectors are not easy to work with. Once you are sure that your calibration is OK you can measure the component. The Smith chart has a readout that will give you the resistance and inductance or capacitance for the marker frequency. As you move the marker you will see the resistance increase on the inductor due to the "skin effect" . The inductor value shown at the marker is calculated by dividing the reactance by 2*pi*frequency. You have to be careful interpreting the results because parasitic capacitance will affect the reactance measured and the estimate of L by this method will get worse as the frequency increases.

I made some tests today on a small air-core inductor that measured 243 nH on a DE-5000 inductance meter at 100 kHz. I then connected it to a calibrated test jig and made some measurements. I attached a series of annotated screenshots showing the estimate of L by the NanoVNA at various frequencies up to 150 MHz. .

I then used the NanoVNA app by OneOfEleven to plot L, R and X versus frequency. You will note that at 50 kHz. the estimate of L is poor compared to my DE-5000 inductance meter. This is because the value of X is very small at this frequency and not in a reasonable measurement range for the NanoVNA. As the frequency increases to about 1 MHz. the accuracy of the estimate improves because the reactance is now a little over 1 ohm. Note the slight rise in calculated L with frequency due to the parasitic capacitance of the inductor.

Roger

Well, the radio is a QRP Pixie kit and it doesn't put out very much power; I just wanted to test if I soldered the connections well. I have an analog multimeter I could use as well. Eventually I plan to get (or make) a dummy load, but I'm still practicing my soldering for now.

The second one is pretty much what I was thinking of. Apparently he is making the Gerbers available.

Hi Barry,

I agree with Arie above.

I wonder if you have seen the slides from my 4 hour presentation on the NanoVNA (some stuff is probably outdated now).


(they are also available in the Files section here)

If you can use anything from those slides, feel free to "steal" anything you want.

73,
Luc ON7DQ / KF0CR

Howard and Rudi,
I have gotten the SWR for the DIY 70watt HF Amp kit to work with a Hermes HL2. It took a 16ohm 5watt or higher resistor across the secondary of the input transformer. If you look closely at some of the minipa100 amp pictures that use the same basic circuit, you will see the 16ohm resistor. This makes sense since the input transformer is a 2:1 ratio or 4x impedance. There is some impedance from the rest of the gate input circuit, so the 16ohms makes sense.

Also, there is a webpage with details on the build and then test and optimization of the amp here:


That reference shows 15ohms as the optimum which would be a reflected 60ohms IF there were no other impedances connected.

The other alternative is to put a Pi resistor pad on the input. This is a good solution for higher power rigs like the ?BITX where you also need to cut the input power to 5 watts.

Be sure to add the low pass filter that is needed on the output of the amp. It is difficult to get the bias just right to not have some harmonics above the allowed levels.

Hope that helps.
73
Evan
AC9TU

On Thu, Feb 11, 2021 at 02:46 PM, daniebjoubert wrote:

John. Great idea.
I will try with my smart phone.
I am also going to try and do a screen p

Hi John,
Attached the screen print before it disappears.
I am grateful for the assistance.
Danie ZS1DBJ

Hi Barry,

It's getting more beautiful every new version, two thumbs up.


About the Smith Chart and losing the audience.

If I explain the Smith Chart to my children (read: listeners) I start telling them that the Smith chart shows the reflection of the sent signal. So how big is the reflection (0-100% compared to the sent signal) and under what phase (+/-?? 0-180dgs) did we measure it. Then what happens if the same load was a bit further away; what would happen to the phaseangle. This is a first eye-opener.

Next: The reflection percentage easily transforms to SWR as a next step. What SWR is 100% reflection, what is SWR at 0% reflection, and at 50% reflection? Where is that on the chart?
And then the formula about relation of SWR and reflection coefficient can be demonstrated with simple ohmic loads leading to SWR=1, 2, and 3

Next comes the part: What Impedance caused that reflection that was measured in the first place.
First introduce simple complex numbers R+jX, what they mean and show some examples. Only after understanding this, I introduce the different Smith chart impedance circles slowly.
Then the forst demo: measure a potmeter on 10MHz and change its value, same for variable inductor and variable capacitor.

This way of introcing the Smith chart is something that a normal ham can use to build on his knowledge he or she already has. Most hams are interested in the nano for SWR measurements and antenna tuning in the first place and getting an impedance of 50 ohms with a tuner.


I've given several presentations about the Smith Chart only. That takes me about 1,5 hours from the start to finish. Last part of the presentations is about? how tuning networks ( like L, pi, of T) behave in the Smith chart and why. Of course I use the nanoVNA as measuring equipment for the demo's.
I've done this live (before COVID) and also online. Everybody had a good understanding of the Chart and could make use of it afterwards.


So.... starting with a Smith Chart with impedance circles is a too big leap. Also folding the rectangular system onto a circle. Might be so, but that kind of math does not help a ham.


My two cents worth. Hope I gave you new ideas.

73 to all and stay safe.

Arie PA3A


Op 14-2-2021 om 17:07 schreef Barry Feierman:

EXAMPLE from DAYS PAST: In the TTL days of logic long past to newbies, it
was common practice to place a black, CK05 (0.1 ?F) capacitor at each end
of a row of logic chips. This was placed between Vcc and return. In those
days, we seldom considered self resonance of a passive device. The
intended use of them on the boards was to keep logic switching noise off
the DC rail. Turns out those CK05 capacitors which peppered our boards
became self resonant somewhere between 1 and 2 MHz, usually around 1.4 to
1.6 MHz. Therefore, above self resonance, they became DC-blocked
inductors. Now, ask yourself: "is an inductor good at bypassing rail noise
as the capacitor was intended to accomplish?" NO!

Several decades ago, I had the privilege of issuing a couple of new-hires
from Kent State into the real world of 'parasitic component' behavior (the
real world they would have to live in). I was given the task as they would
specify totally unrealistic component values for designs and had only an
understanding of the ideal behavior of electronic components. I asked
them to check out a small handful of those CK05 capacitors from engineering
stock. We warmed up the HP impedance meter of the time (the one that had a
tunable drum as a frequency indicator and topped out at 110 MHz). Sure
enough, *EVERY* CK05 capacitor went purely resistive between 1.4 and 1.6
MHz and inductive above that. Their eyes bugged out. They could not
understand or comprehend how a capacitor could possibly become resonant
(+jX = -jX) and ultimately become an inductor. I sent them back to their
test books and pointed them in the direction of our local building
library. It took them a week of digging, but they finally came back with
the classic capacitance to resistance to inductance curve with frequency.

Dave - W?LEV

On Sun, Feb 14, 2021 at 2:26 PM Manfred Mornhinweg <manfred@...>
wrote:

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.

--
*Dave - W?LEV*
*Just Let Darwin Work*

On Sun, Feb 14, 2021 at 05:04 PM, Howard Fidel wrote:

I found that the 70 watt kit on eBay

Hello Howard,
Do you have this one bought?


I could not make it to work.

Instead I build this 45W kit:


73, Rudi DL5FA

* Nano VNA overview by K3EUI Barry *

Each time I give a "talk" on the Nano VNA I learn something new. I've given five talks now, and from the questions from listeners, I know where the hurdles are.

1) Calibration of the VNA - where you do the calibrations matters. Why?

2) Impedance varies with coax feed line length... but why?
And (mostly) SWR does NOT change with small feed line changes - why?
This is a key concept, not easily seen by most of us.
The "reflection coefficient" is established right at the antenna-feed line junction.

3) SWR vs. RETURN LOSS
They are both saying the same thing, with different units (SWR has no units, RL is in dB)

4) The magic of the Smith Chart: can we get over the anxiety? Think of it like a DART BOARD
An antenna can have some RESISTANCE and some REACTANCE.
The Smith Chart just shows you R and X, for each frequency you plot.
Of course, the Smith Chart does not show you POWER output, but does show SWR indirectly by how far
your data are from the Bull's Eye (if standardized at 50 ohm).
I included a few slides to illustrate this concept - maybe lost my audience here.

5) Resonance - when measured at the END of your coax, if not 1/2 wavelength, or multiple of 1/2 wavelength
When the reactance is zero, this is resonance.
But the resistance may not be close to your coax's 50 ohm. That sounds simple enough.
But resonance is NOT (necessarily) where the SWR will be lowest as measured in your shack.
A one-wave dipole, center fed, won't match to 50 ohm coax, but it might be "resonant".

6) What happens when you add an "Antenna Tuner" in your shack? The rig sees a SWR of 1:1
but meanwhile, what is happening on your feed line to the antenna?
Is the "forward power" really greater than the power emerging from the rig? Yikes... magic?

Comments on my latest (but not last) PPT will be appreciated by me.
I now have some experience with the S21 (two port) measurements of filters.
My next project: investigate the isolation of a 2m/70cm diplexer (Comet) with nano VNA

TU for all of the feeback off list
Feel free to share this pdf,

de k3eui Barry

I use my nanoVNA to test the input swr. I found that the 70 watt kit on eBay has a high SWR at the input on some bands. I am in the process of optimizing that now.