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how do we correct an S21 measurement?

Has anyone looked at S21 for a mixer as DUT,
where other mixer input is e.g. sinusoid or sawtooth?

37 : ann : the uncertainties of our nanovna will be estimated tomorrow

For the record, Nanovna-saver looks for Nanovna USB id's

For the Nanovna-F I get:
usb 3-11: new full-speed USB device number 20 using xhci_hcd
[13509.779971] usb 3-11: New USB device found, idVendor=0483,
idProduct=5740, bcdDevice= 2.00
[13509.779976] usb 3-11: New USB device strings: Mfr=1, Product=2,
SerialNumber=3
[13509.779978] usb 3-11: Product: NanoVnaPro Virtual ComPort
[13509.779980] usb 3-11: Manufacturer: SYSJOINT
[13509.779982] usb 3-11: SerialNumber: 00000000001A
[13509.783606] cdc_acm 3-11:1.0: ttyACM1: USB ACM device

thanks, the smith chart tutorial was nice, the matching network I'm dealing with is a bit more involved as it consists of an emc low pass filter on the rfid chip amp, then the matching L network going to the coil antenna, there are some useful tools provided by the chip manufacturer to design the matching circuitry but the parameter I'm missing is the parallel R at resonance, I don't think it's equivalent to the DC resistance of the coil... so that's where I'm a bit stuck trying to figure out a way to measure it.

Sweet!
Nice work.?



On Sun, 6 Oct 2019 at 3:06 PM, Oristo<ormpoa@...> wrote: > If you'd like to make this diagram slightly narrower,

the right-most rows on calibrate and format could be made to go vertically down.

Like this??

The S Parameters are defined in terms of a circuit within a closed box. Snm is the amplitude of the signal coming out of port n relative to the signal that went into port m. Thus, S21 is the signal that comes out of port 2 relative to what went into port 1. For a two port network that is the transmitted signal. S11 is what comes out of Port 1 relative to what goes into Port 1, so it is the reflected signal. All ports are assumed to be terminated in a matched impedance for whatever you use as the calibration impedance. This means there are no reflections off the generator or the external loads.

Some textbooks explain this more clearly than others.

One important thing to note is that for passive networks, i.e. no amplifiers or other sources, S21=S12.

I do a lot of analysis of N port networks for coupled cavity systems. These are to understand the properties of rf linear accelerators, which are nothing more than a type of bandpass filter. I find the chain matrix notation more useful than S Parameters. The chain matrix, sometimes called the ABCD matrix, relates the voltages and currents at one set of terminals, the input, to the voltages and currents at another set of terminals. For a two port network with voltage V1 and current I1 a the input and V2 and I2 at the output this gives the circuit equations V2=A*V1+B*I1 and I2=C*V1+D*I1. Note that the conventional definition of the current is that I1 is into the network and I2 is out of the network.

Given the voltage and current at a terminal the incoming wave amplitude a and outgoing wave amplitude b can be defined as a=0.5*(V/sqrt(Z0)+I*sqrt(Z0)), and b=0.5*(V/sqrt(Z0)-I*sqrt(Z0)). The scaling isn't important since the S Parameters are ratios of outgoing waves to incoming waves, but you can set it so the sum of all a^2 equals the total power input.

There is another way to look at networks called the impedance matrix which relates all terminal voltages to all terminal currents. This is what you usually get by applying Kirchoff's law to a circuit.

The point of the above is that you can use ordinary circuit analysis to a network and calculate the S Parameters to develop an understanding of how they relate to the parameters of an ordinary circuit, such as an inductor, capacitor, resistor or resonator.

This can involve a lot of messy algebra, which can easily get screwed up by mistakes. I find Mathematica to be a powerful tool, although sometimes it takes some effort to get an algebraic result in a "neat" form.

The NanoVNA is a pretty amazing instrument for its price. I think it is good not to confuse it with a laboratory instrument, but it is a great learning tool. It also has an immediate application that is useful to Radio Amateurs, understanding antennas and filters.

I have enjoyed following the discussions in this forum.

73 de K9GXC, Jim

If you'd like to make this diagram slightly narrower,
the right-most rows on calibrate and format could be made to go vertically down.

Like this?

If you'd like to make this diagram slightly narrower, the right-most rows on calibrate and format could be made to go vertically down.



On Sun, 6 Oct 2019 at 2:48 PM, Oristo<ormpoa@...> wrote: Oops, previous menu gif background was light gray;
whitened:

Oops, previous menu gif background was light gray;
whitened:

If the NanoVNA could provide a negative Electrical delay it could be fixed.

There is at least room in the firmware menu to add a "negative delay" menu item, under e.g. "CONFIG"..

Something that I have never fully understood is that S21 is supposed to be measured using a "matched load". Isn't the "matched load" of a VNA equal to 50 ohms? Are we to assume that 50 ohms is the only possible "matched load"? Or can a VNA be calibrated for any value of "matched load"?

Also, LTspice from Linear Technology (now part of Analog Devices) has been freely avaiable for a long time. There is a Yahoo group, LTspice, which provides excellent support and information.

DaveD

Sent from a small flat thingy

Sean,Are you aware that the simulation software call MicroCap is now free?

Try simulation first to give you a rough idea of your component values, then prototype and test.?
Regards
Larry

On Sun, 6 Oct 2019 at 12:34 PM, sean@...<sean@...> wrote: I am aware of that, like I said, I'm new to RF, but I understand that without a non reactive part of impedance in the antenna, there's no power going into the antenna right?? If the LC is at resonance, the impedance is infinite, therefore, there can be no watts.? I am assuming the parallel R at resonance partly consists of the power radiated into space, and partly other effects of the current flowing through the LC tank.? In the case of RFID, because the passive receiver is powered by the RF field, part of the power sent to the antenna is dissipated in the receiver circuitry through coupling.? What I'm trying to figure out is: am I chasing the right thing when it comes to designing a matching network?? and is the nanoVNA capable of measuring the real component of impedance at the resonant frequency with any accuracy.

On Sun, 6 Oct 2019 at 12:34, <sean@...> wrote:

What I'm trying to figure out is: am I chasing the right thing when it comes to designing a matching network?

With respect to matching networks, have you seen W2AEW's Youtube
channel?
Also, do follow the link to W0QE's Youtube channel: SimSmith is very
nice software.

--buck

Very nice, thanks.?



On Sun, 6 Oct 2019 at 11:45 AM, Oristo<ormpoa@...> wrote: > > I hope there will be no objection to me sharing

HTML is in public domain

Easier to print:

Yes, I meant correction.You have a save menu after the correction button.. shouldn't be one. Correction is on or off.I still think reset should be at the top of the list and save after calibrate steps.?


On Sun, 6 Oct 2019 at 11:33 AM, Oristo<ormpoa@...> wrote: Hi Larry -

When you click the DFU menu button, you get the next menu with 2 items:
Reset and Enter DFU and Cancel.

OK, I never dared press DFU
and anyway added a slide switch for hard DFU,
too often required for hangs..

The full word:. Calibration is a switch that can be inverted text
to show calibration is being applied,
or normal text to show calibration is not being applied.?

OK, I see "CORRECTION", not "Calibration"

How often do you turn it on or off?

Maybe raw data helps understanding impact of shielding and layout changes?

I am aware of that, like I said, I'm new to RF, but I understand that without a non reactive part of impedance in the antenna, there's no power going into the antenna right? If the LC is at resonance, the impedance is infinite, therefore, there can be no watts. I am assuming the parallel R at resonance partly consists of the power radiated into space, and partly other effects of the current flowing through the LC tank. In the case of RFID, because the passive receiver is powered by the RF field, part of the power sent to the antenna is dissipated in the receiver circuitry through coupling. What I'm trying to figure out is: am I chasing the right thing when it comes to designing a matching network? and is the nanoVNA capable of measuring the real component of impedance at the resonant frequency with any accuracy.

Hi aa--something
Cables length as such has basicly no influence. Consider the cable as part of the hardware system, they are calibrated away.
The only effect is small potential phase variation if the cable are bended between calibration and connecting to a DUT.
Some cable are more phase stable than others
Kind regards
Kurt

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Sendt: 6. oktober 2019 15:01
Til: [email protected]
Emne: Re: [nanovna-users] Inductor S21 measurement using nanoVNA

Hi,
I replaced the cables with much shorter ones, and re-calibrated using these 2 new cables (see attached photos), and I am getting the same results. Not sure the cables interfere with the nanoVNA results. As far as I remember, cables longer than wave length/8, I should worry about transmission line effects. However, in this case, the cables are 10 cm long each, and the subject frequency is 60MHz.

Thank you Erik, that explains it, an image.? So I just ignore the lower frequency of the two peaks.? And it's possible to calibrate the amplitude.? I will try the test of seeing the FM BC band with an antenna.
Bob

See /g/nanovna-users/topic/34079496#3464