Re: Measuring Inductance.
If you¡¯re looking to refine your measurement repeatability, do a fresh recal, repeat the sweeps of both induntors under as near exact conditions possible, then recheck your cal to confirm measurement integrity was maintained between cals.
Switches can frustrate repeatability, so its important to have a handle on tolerances in your measurements.
It¡¯s always good practice to do end of test cal checks, and to quantify the variability between duplicate measurements. Its an easy method for determining the boundaries of uncertainty that are attributable to the quality of your test equipment and processes, while also validating the integrity of your results.
--
73
Gary, N3GO
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Re: Measuring Inductance.
Joe,
Once you have measured and installed the coil and capacitors in the RF Amplifier you can tweak the settings to compensate for stray capacitance and inductance by measuring the 50 ohm output impedance in the amplifier by simulating the RF Plate resistance.
BEFORE YOU DO THIS MEASUREMENT VERIFY THE AMPLIFIER IS POWERED DOWN AND PLACE A SHORT ACROSS THE POWER FILTER CAPACITORS TO DISCHARGE THE CAPACITORS!
- Place the RF Tube in it's socket. This will simulate the tube capacitance.
The ARRL handbook gives the following approximation formula for calculating the load
resistance of a vacuum tube power amplifier:
Vp
Rl = ----
KIp
where K is 1.5 for class AB, 1.57 for class B, and 2 for class C.
Calculate and install a non-inductive resistor from tube late to ground to simulate the Plate load.
- Install the NanoVNA on the RF Output connector
- Set the PI Network Capacitors and Coil for each band and adjust the capacitors (and coil tap if necessary) to get the output impedance close to 50 +j0 ohms.
The plate formula is an approximation but these measurements will get you into the ballpark.
- Remove the resistor before operating the amplifier.
BEFORE YOU DO THIS MEASUREMENT VERIFY THE AMPLIFIER IS POWERED DOWN AND PLACE A SHORT ACROSS THE POWER FILTER CAPACITORS TO DISCHARGE THE CAPACITORS!
I used to repair and install Marine MF (2 to 4 Mhz) radios on boats when I was in college 45 years ago. I had to adjust the output series coil to resonate the 20 foot whip antenna. I was I had the NanoVNA back in those days!
73 Mike N2MS
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On 09/11/2021 1:22 PM Joe WB9SBD <nss@...> wrote:
Well,
I left the coils in place in the amp, BUT.... I lifted all the taps, so
the coil is floating free but inside the amp.
And all readings are normal now. Interesting.
So OK we planned on leaving the taps on 80, 40, 20, as they are, just
add the extra "L" using the tubing coil.
So thats what I just did, I found suitable and convenient taps for 10 =
1.1uH and for 15= 1.8uH.
So original was
80= 11.6
40= 5.6
20= 2.06
15= .936
10= .448
Now is,
10 = 1.1uH
15 = 1.8uH
20= 2.94uH
40= 6.46uH
80= 12.46uH
The switch must be messing with the readings when all connected.
So next step is now the reverse matching thing. wish me luck.
Joe WB9SBD
On 9/11/2021 12:15 PM, Gary O'Neil wrote:
The rotations on the Smith chart generally imply of resonance. The resonant frequency is where the trace crosses the real axis. It sounds like you may have moved the SRF inband.
Don¡¯t change your setup, but remeasure the first coil. If you repeat your original result, you can conclude that your test configuration is probably correct and sound. Beyond that, trust the measurements. For collateral confirmation, enter the coil dimensions into one of the online solenoid coil calculators, and compare the predicted inductance values for ballpark agreement with your measurements.
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Re: Measuring Inductance.
Well,
I left the coils in place in the amp, BUT.... I lifted all the taps, so the coil is floating free but inside the amp.
And all readings are normal now. Interesting.
So OK we planned on leaving the taps on 80, 40, 20, as they are, just add the extra "L" using the tubing coil.
So thats what I just did, I found suitable and convenient taps for 10 = 1.1uH and for 15= 1.8uH.
So original was
80= 11.6
40= 5.6
20= 2.06
15= .936
10= .448
Now is,
10 = 1.1uH
15 = 1.8uH
20= 2.94uH
40= 6.46uH
80= 12.46uH
The switch must be messing with the readings when all connected.
So next step is now the reverse matching thing. wish me luck.
Joe WB9SBD
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On 9/11/2021 12:15 PM, Gary O'Neil wrote: The rotations on the Smith chart generally imply of resonance. The resonant frequency is where the trace crosses the real axis. It sounds like you may have moved the SRF inband.
Don¡¯t change your setup, but remeasure the first coil. If you repeat your original result, you can conclude that your test configuration is probably correct and sound. Beyond that, trust the measurements. For collateral confirmation, enter the coil dimensions into one of the online solenoid coil calculators, and compare the predicted inductance values for ballpark agreement with your measurements.
|
Re: Measuring Inductance.
The rotations on the Smith chart generally imply of resonance. The resonant frequency is where the trace crosses the real axis. It sounds like you may have moved the SRF inband.
Don¡¯t change your setup, but remeasure the first coil. If you repeat your original result, you can conclude that your test configuration is probably correct and sound. Beyond that, trust the measurements. For collateral confirmation, enter the coil dimensions into one of the online solenoid coil calculators, and compare the predicted inductance values for ballpark agreement with your measurements.
--
73
Gary, N3GO
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Re: Measuring Inductance.
Not identical coil.
I needed slightly more "L" on every band. so I made the 10/15 meter coil slightly bigger.
You see the coil.
3/16" tubing, 7 turns, 1.75 diameter 2.25 long.
New coil,
3/16" tubing also 7 turns, BUT 2.25 diameter, and 2.25 long.
So it should have slightly more "L".
I don't understand why now I am getting the 2 rotations on the smith chart.
Joe WB9SBD
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On 9/11/2021 10:25 AM, Gary O'Neil wrote: Identical coil identical set up identical results. Not true? Something not identical. Check set up.
At first blush it looks like you connected the coils in parallel. That would make the tests Not identical.
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Re: Measuring Inductance.
Identical coil identical set up identical results. Not true? Something not identical. Check set up.
At first blush it looks like you connected the coils in parallel. That would make the tests Not identical.
--
73
Gary, N3GO
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Re: Basic Output Definitions
Allow me to take a stab at this and try not to introduce too many new issues.
1) The 'phase' can be viewed as the 'delay' between the input signal and the output signal. When considering scattering parameters, the signal being measured is usually a 'voltage'. Any 'delay' indicates the presence of reactance in the circuit. (OK, I have to complicate this a bit. For one port devices where there is only one electrical node one can measure, one can still think of an 'input signal' and an 'output signal' which are simply 'added' to produce the measured signal.)
2) The terms 'real part' and 'imaginary part' are meaningless if no 'of' is included. For example, I may report a measurement has a "real part of .1". The question is, are we talking about the 'real part of the reflection coefficient' or the 'real part of the impedance'. Stated simply, "No 'of', no meaning".
As for the Smith chart, the plot is one of the 'real/imaginary parts of the voltage reflection coefficient' but the circles are the 'real and imaginary parts' of the impedance. Usually, a marker reports the 'real/imag' part of the impedance but that is wholly product dependent.
3) They MAY be the same, it depends on the 'of'...... If the real/imag refer to the voltage reflection coefficient then they will be different than the impedance. But... if real/imag is 'of' the impedance, they would be the same (by definition).
4) Spp parameters are ratios and are therefore unitless. The vast majority of Scattering Parameter papers discuss the ratios of VOLTAGES. A few use the term to refer to Power Ratios. ( I implore people to avoid the trap of arguing the 'proper' definition. I understand there are two camps. I have found it to be a fruitless discussion as it generally devolves into a 'Holy War'.) For the newly initiated, one can safely assume Spp refers to a voltage ratio.
Hope that helps.
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Re: Basic Output Definitions
That reference (below) is excellent, and clarifies everything! Thanks, Roger.
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Here is a link to an excellent paper by Olivier Pilloud HB9CEM which describes the relationship between the reflection coefficient Gamma (¦£). complex impedance (R+jX), Return Loss and VSWR. He also shows how the rectangular plot, polar plot and Smith chart are overlaid. He finishes up with an example and plots the results.
IHope it helps you - Roger
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Hello All,
Need a question answered here.
I am the one here making a new set of coils for a Heathkit SB-220.
Using A NanoVNA-H4 I learned how to measure the old coil values. And what the stimulus range needed to be to measure the whole range of taps on the coil to the best resolution.. I got values that were very close to what was expected.
And on the smith chart it was a single arc curve.
Now I have installed the new coil.
And measured the coil so I can determine where to attach the last two taps to have the correct amount of "L" for each one.
BUT.... and there always is a BUT isn't there?
Using the exact same test parameters, now I have a smith chart that is two turns.? Why would that be? The measured values one is close to what is expected 2.2uH the other smith loop is 1.09uH.
What's happening here, and why is it different?
Joe WB9SBD
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From the beginning:
Many of the questions that appear in this forum regarding VNA operation suggest the fundamental premise of the VNA is either missing, misunderstood, assumed, or ignored. Questions elicit a barrage of responses; most of which are appropriately motivated, but not always helpful or instructive.
Often; original posters become silent while threads evolve and drone on until eventually terminating open ended; with final posts sometimes unrelated to the question originally asked. This is common on forums, but it is not efficient toward establishing a knowledge base.
The scope of questions as well as most answers to them overlook the obvious but simple detail that all VNA's only produce one output result per measurement. That result can be presented to a user in a plethora of data formats, with the most common format being a complex number pair referred to as a voltage reflection coefficient or simply reflection coefficient, and only one VNA port is utilized for the measurement. Measurements between ports are called transmission coefficients and are used for insertion loss (gain), delay, isolation, etc. measurements. Armed with the measured coefficient(s), the frequency at which the measurement was made, and an accurately affixed known reference called the characteristic impedance or Z0, all other data formats are derived through mathematical manipulation.
By the above; the entire essence of a VNA is to make one or more complex voltage (amplitude and phase) measurements. It is precisely analogous to an AC voltmeter. Other than the operational tasks of physically connecting to, calibrating, and performing the measurements; knowledge of how the hardware acquires and presents its results neither adds to nor detracts from the instruments capability, utility, and usefulness of the device to a user.
What now becomes glaringly obvious is that beyond the powerful measurement capability and utility of a VNA, modern instruments include an equally powerful embedded feature that performs involved complex mathematical computations in real time with the measurements being made. Analogous to a pre-programmed, fully automatic graphing calculator, the VNA produces a family of tabular and graphical displays of the most common RF parameters and formats of interests to engineers and technicians.
A key point here is that the measured results presented by the VNA are precisely identical, no matter the format in which they are presented. Unless it has been determined that a bug exists in the VNA software/firmware; users can take it on faith that the parameters are accurate as presented; assuming the instrument is being utilized as dictated by its design.
Inasmuch the various data formats are used, related, manipulated, interpreted, etc., operation of the VNA should be and remain transparent to discussions regarding data format relationships. Motivated users can (and should) pursue an understanding of the underlying mathematics of scattering parameters, complex numbers, and linear algebra to the extent required to meet their needs.
In most cases, users are interested in a particular measurement detail; e.g. impedance, VSWR, gain, etc., and alternative data formats have little if any relevance. In other cases they may find utility in the convenience of format conversion; e.g. inductance to reactance, phase to delay, etc.; all being computationally derived from identical measurement.data.
For users who are just becoming familiar with VNAs and their applications; an intuitive understanding and acceptance of the fundamental premise of VNA measurements as described here should sufficiently allow easy access to most of the utility that VNAs provide, and inspire the pursuit of deeper understanding of the relationship and derivation of all the parameters used to define RF networks.
--
73
Gary, N3GO
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Re: Basic Output Definitions
Andy,
Here is a link to an excellent paper by Olivier Pilloud HB9CEM which describes the relationship between the reflection coefficient Gamma (¦£). complex impedance (R+jX), Return Loss and VSWR. He also shows how the rectangular plot, polar plot and Smith chart are overlaid. He finishes up with an example and plots the results.
IHope it helps you - Roger
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Re: Basic Output Definitions
Wonderful! Thanks, Jean-Roger
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On Sep 10, 2021, at 4:28 AM, F6EGK - Jean-Roger <F6EGK@...> wrote:
Andy,
Below is a copy /paste of my answer to another old thread. It could be of interest for your question 3.
REAL and IMAG parameters are not the samething as RESISTANCE and REACTANCE parameters. REAL and IMAG apply to reflection coefficient ¦£, in its complex form (a+j.b). That's why values are always in the [-1,1] interval, without any associated unit. When REAL=-1 and IMAG=0, it is the Short circuit situation. When REAL=1 and IMAG=0, it is the Open circuit situation. When REAL=0 and IMAG=0, it is the normal Loaded (50 ohms) situation.
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Re: NanoVNA firmvare, compiled by DiSlord
#firmware
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Re: Basic Output Definitions
Andy,
Below is a copy /paste of my answer to another old thread. It could be of interest for your question 3.
REAL and IMAG parameters are not the samething as RESISTANCE and REACTANCE parameters. REAL and IMAG apply to reflection coefficient ¦£, in its complex form (a+j.b). That's why values are always in the [-1,1] interval, without any associated unit. When REAL=-1 and IMAG=0, it is the Short circuit situation. When REAL=1 and IMAG=0, it is the Open circuit situation. When REAL=0 and IMAG=0, it is the normal Loaded (50 ohms) situation.
LINEAR is the ¦£ modulus form of combined REAL and IMAG values, and finally POLAR is the geometric representation of REAL, IMAG and PHASE values. When POLAR is displayed by the NanoVNA, and even if data values are exactly displayed as for Smith Chart, results must not be read in the same way. Have a try by displaying two CH0 traces, POLAR and SMITH.
SWR and LOGMAG (Return Loss) are derivated from ¦£ modulus (LINEAR). For educational purposes I have created an ods file (see below), showing and calculating NanoVNA parameters. You can play with it by entering values in the blue fields, and also checking what are the arithmetic relations behind the different results. Here Group Delay is not relevant as calculations are done for a discrete (CW) frequency.
A last word about the use of REAL and IMAG parameters. The following case (see attachment) is an opened coaxial cable (length 2 meters), creating a quarter wave stub (at red marker). An opened coaxial cable remains a good use case for education and increase of knowledge. On the NanoVNAsaver snapshot we see clearly that displayed values between RESISTANCE/REACTANCE and REAL/IMAG do not allow an immediate comparison. For example at red marker, R+jX or Smith Chart highlight a value of 0+j0 ohms (short circuit situation), and checking this with REAL/IMAG chart you get -1 (REAL) and 0 (IMAG) which is the same thing. Be careful with REAL and IMAG curves which follow sinus and cosinus rules, it reflects simply a monotonous variation of PHASE.
REAL is also interesting if you want to measure a coaxial cable length, thanks to advanced TDR function.
73 from Jean-Roger / F6EGK
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The group has a very well built wiki. Please read it there as well. If this seems like a lot at first reading because your problem is hard to put on any description, set it aside for a while, read it again, and understand what you need to do. It's not such a big deal, believe me.
You should not believe all the answers of your computer regarding the driver. Think and act. When I first installed the DefuSe Demo, I also installed the driver and later there was never an issue with the lack of a driver. Yes, in old age, the human brain has a hard time understanding what others are doing out of routine at a young age. Maybe that¡¯s why they¡¯re looking for template descriptions who run into errors. Each operating system uses a file manager. This file manager should be used to find the required drivers at the DefuSe Demo installation site. Not only does a ¡°good priest learn to his death,¡± we also need to continually learn in an ever-changing world to understand and follow change.
Gyula HA3HZ
--
*** If you are not part of the solution, then you are the problem. ( ) ***
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Re: Basic Output Definitions
Thanks, Dave. Note that the images you sent did not come to me, only the place-holders (see below). Also, I may have been unclear. I totally understand that resistance and reactance are quite different, but I am wondering why the Real number on the polar chart is nowhere near the Resistance reported when R is output, and why the imaginary part of the polar chart (dropping off the j) is nowhere near the reactance reported when that is the output. In other words, isn¡¯t the real part of the complex number equal to resistance and the imaginary part equal to reactance? But the nanoVNA gives VERY different values¡
Andy
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[image: image.png]
2. ¡°Polar is same as Smith chart but with complex reactance rather than L
or C shown.¡± Yes, the trace is identical to Smith, but why are the real
and imaginary numbers reported nowheres near the R and X reported by
Resistance and Reactance outputs?
The following two charts from a course I once taught express the mapping
between ¡À jX and their equivalent lumped equiivalent form. As noted above
and below, they are both frequency dependent, can not dissipate power by
themselves (in the ideal model), and can be associated with external
fields. The resistance term of the impedance expression is frequency
independent, can and does dissipate power, and is not associated with
external fields. Yet another difference: 1) resistance can not modify or
change phase relationships between current and voltage, and 2) reactance
indeed can and does modify or change the phase relationships between
current and voltage.
[image: image.png]
[image: image.png]
3. Likewise, Real and Imaginary have no similarity to Resistance and
Reactance; shouldn¡¯t they be the same?
Absolutely not the same !!! Consider the above two charts. They should
make it clear why resistance and reactance are not the same. iI've also
pointed out the difference between resistance and reactance - the ¡À jX term
of the total impedance expression.
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Re: Basic Output Definitions
1. ¡°Phase is the relative phase difference between source and received signals.¡± What does this really mean? Is it current to voltage phase, or change in that as influenced by the DUT, or simply phase change of voltage alone, or¡? The phase represents the voltage/current offset produced by the DUT (Device Under Test) as measured by the NANOVNA. Generally, voltage is 180-degrees out of phase with current - high current ===> low voltage and low current ===> high voltage. So the two are 180-degrees, or ¦Ð-radians, out of phase with each other. The 180-degree phase difference between current and voltage applies strictly to resistive loads with no reactance - the ¡À jX term in the complete impedance expressioin: Z = R ¡À jX. Z = total impdeance, R = resistive term, ¡À jX = reactive term. Introduction of a complex portion of the impedance measurement skews the voltage/current phase relationship to something other than the resistive 180-degree offset. [image: image.png] 2. ¡°Polar is same as Smith chart but with complex reactance rather than L or C shown.¡± Yes, the trace is identical to Smith, but why are the real and imaginary numbers reported nowheres near the R and X reported by Resistance and Reactance outputs? The following two charts from a course I once taught express the mapping between ¡À jX and their equivalent lumped equiivalent form. As noted above and below, they are both frequency dependent, can not dissipate power by themselves (in the ideal model), and can be associated with external fields. The resistance term of the impedance expression is frequency independent, can and does dissipate power, and is not associated with external fields. Yet another difference: 1) resistance can not modify or change phase relationships between current and voltage, and 2) reactance indeed can and does modify or change the phase relationships between current and voltage. [image: image.png] [image: image.png] 3. Likewise, Real and Imaginary have no similarity to Resistance and Reactance; shouldn¡¯t they be the same? Absolutely not the same !!! Consider the above two charts. They should make it clear why resistance and reactance are not the same. iI've also pointed out the difference between resistance and reactance - the ¡À jX term of the total impedance expression. 4. Everyone says that the VNA reports S11 and S21; I get that these are reflection and transmission, but what are the units (or dimensions)? Is it voltage, or power, or current¡? S-Parameters in their pure form are vector power measurements. There are a number of ways they can be reported. For S11: 1) a simple numerical ratio (in its simplest form) of input vs reflected powers, 2) that numerical ratio expressed in dB, 3) numerical ratio of the reflection coefficient, and 4) numerical ratio of the reflection coefficient expressen in dB. dB is all base 10 as we are dealing with power. For S22: 1) a simple numerical ratio of input power vs. transmitted power, 2) that numerical ratio expressed in dB. Note that S22 as measured on the "output" side of the DUT is the equivalent of S11 on the "input" side of the DUT, both with the opposite port properly terminated. The transmission measurement for impedance, S21, really has no meaning (no Smith Chart applicability). The measurement for the output port of impedance is S22. Dave - W?LEV On Thu, Sep 9, 2021 at 3:11 PM Andrew Kurtz via groups.io <adkurtz= [email protected]> wrote: I have been through the Wiki and got some answers, but here are some
questions about the output options on the nanoVNA-H4:
1. ¡°Phase is the relative phase difference between source and received
signals.¡± What does this really mean? Is it current to voltage phase, or
change in that as influenced by the DUT, or simply phase change of voltage
alone, or¡?
2. ¡°Polar is same as Smith chart but with complex reactance rather than L
or C shown.¡± Yes, the trace is identical to Smith, but why are the real
and imaginary numbers reported nowheres near the R and X reported by
Resistance and Reactance outputs?
3. Likewise, Real and Imaginary have no similarity to Resistance and
Reactance; shouldn¡¯t they be the same?
4. Everyone says that the VNA reports S11 and S21; I get that these are
reflection and transmission, but what are the units (or dimensions)? Is it
voltage, or power, or current¡?
Thanks!
Andy
-- *Dave - W?LEV* *Just Let Darwin Work*
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Re: Basic Output Definitions
1. Voltage, Output vs Input 2. Takes more time than I have to explain. 3. Ditto. 4. S11 and S21 are ratios (dB actually, which is really just a ratio) of voltages. S11 = 20*log(Vreflected/Vincident). S21 = 20*log(Voutput/Vinput) On Thu, Sep 9, 2021 at 11:11 AM Andrew Kurtz via groups.io <adkurtz= [email protected]> wrote: I have been through the Wiki and got some answers, but here are some
questions about the output options on the nanoVNA-H4:
1. ¡°Phase is the relative phase difference between source and received
signals.¡± What does this really mean? Is it current to voltage phase, or
change in that as influenced by the DUT, or simply phase change of voltage
alone, or¡?
2. ¡°Polar is same as Smith chart but with complex reactance rather than L
or C shown.¡± Yes, the trace is identical to Smith, but why are the real
and imaginary numbers reported nowheres near the R and X reported by
Resistance and Reactance outputs?
3. Likewise, Real and Imaginary have no similarity to Resistance and
Reactance; shouldn¡¯t they be the same?
4. Everyone says that the VNA reports S11 and S21; I get that these are
reflection and transmission, but what are the units (or dimensions)? Is it
voltage, or power, or current¡?
Thanks!
Andy
-- Carey Fisher careyfisher@...
|
I have been through the Wiki and got some answers, but here are some questions about the output options on the nanoVNA-H4:
1. ¡°Phase is the relative phase difference between source and received signals.¡± What does this really mean? Is it current to voltage phase, or change in that as influenced by the DUT, or simply phase change of voltage alone, or¡?
2. ¡°Polar is same as Smith chart but with complex reactance rather than L or C shown.¡± Yes, the trace is identical to Smith, but why are the real and imaginary numbers reported nowheres near the R and X reported by Resistance and Reactance outputs?
3. Likewise, Real and Imaginary have no similarity to Resistance and Reactance; shouldn¡¯t they be the same?
4. Everyone says that the VNA reports S11 and S21; I get that these are reflection and transmission, but what are the units (or dimensions)? Is it voltage, or power, or current¡?
Thanks!
Andy
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Re: NanoVNA-App 1.1.207 crashes , 1.1.206 does not
I can't write or debug software for units I don't have I'm afraid (I don't have a V2plus4), it's like trying to find faults on a car you don't have or have never seen, you need the car there with you to run tests on.
Anyway, to be honest I've moved on now, am doing other things these days.
Thanks for all the thanks.
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Roger Need
Gyula Molnar
