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i added a bluetooth module to my sark100 and can now measure "wireless" (use smartphone to display sweeps)

dg9bfc sigi

Am 10.06.2023 um 16:33 schrieb KK4ITX John via groups.io:

On 6/10/23 7:36 AM, Anne Ranch wrote:

The calculations are in ./Windows/TDR.py (not ./Charts/TDR.py, that's what actually does the plotting)
Little discouraging, but I found the same "source code ".....
I also realized that , also little to late nanoVNASaver is "just the GUI" , but I had to start somewhere...

Not at all - NanoVNA-Saver also does the calculations - for calibration, for instance, as well as TDR.

My next step is to find the actual TDR processing,,,

It's in ./Windows/TDR.py

Maybe after I muddle thru the nanoVNASaver TDR undocumented / uncommented source code

If you know how inverse FFT to generate the time domain works, there's really not a lot of commenting needed.

There's the following steps:

1) concatenate all the segment sweeps into one array
2) apply a suitable window (it uses the blackman window from numpy)

3) do the inverse FFT (also in numpy)


Now you've got the time domain impulse response
4) To convert that to a step response (because that's what you need for a impedance display) you convolve it with a step (array of all ones) (yeah, using numpy )

5) Then convert the step response to impedance using the usual Z0 * (1+rho)/(1-rho) formula.

( quite expected ) I will make (some) more progress.
BTW - for all those who keep telling me to "use S11 " phase reversal " - this TDR GUI does use S11 , so
it looks as TDR GUI is "just another layer" of software...
I am still in KISS mode - TDR in principle is
" start timer, then send a pulse and measure time when such pulse returns "
it cannot be much simpler,

That's one way to do TDR - but that's now how VNAs do it. What a VNA does is measure the reflection coefficient at a series of frequencies. That gives you a frequency domain response. Then, you use the Fourier transform to turn that into the time domain response.

As of today - I still do not know how nanoVNA generates such pulse and how "sweep" frequency (?) setup
is related to this simple principle of sending a pulse down the line.

It's not.

That pulse down the line is (idealized) an "impulse" which contains all frequencies. The impulse response (what you get with classic TDR) is the reflected voltage vs time from that pulse. The challenge is that you want a fair amount of energy in the pulse (so your reflection measurement has good SNR) AND you want it to be really narrow, which means a high voltage fast pulse, which is hard to generate. It also might "break" something in the system to put a HV pulse. The problem with a short pulse is that although it's "wideband" the energy is spread out, so the power at any one frequency is small.

What the VNA does is rather than send an infinitesimally short pulse, it sends single frequencies, for a long time, at lower power. It eventually sends "all frequencies" (or, at least enough different frequencies) so it's spanning the spectrum, just like the short impulse did. Even better, each of those individual measurements has more energy, hence better SNR. The Fourier Transform lets you convert all those individual measurements spanning the frequency into an equivalent time response.

For what it's worth, a similar technique is used in modern radars - A radar is just TDR through the air. The shorter the pulse, the higher the resolution, the more power in the pulse, the better the SNR. But the problem is that there's a maximum power (can't keep building bigger tubes or amplifiers - and high power breakdown limits how much power you can push) - so they do what's called pulse compression - they turn the short impulse into a little FM chirp - same average power, but lower peak power. Then on receipt of the signal, they dechirp it to generate the time domain response. In traditional pulse compression they use dispersive delay lines (or these days DSP) - and, as a practical matter, you don't have to use chirps, you can use PSK coding too. But overall, it's the same general idea you use the time domain/frequency domain swap.

PS
When this is all done I may break down and
open the RG6 I have
observe the dielectric - my guess it is poly-whatever
and actually use nanoVNA to measure the VF...
what a goal...
ah yes - my current cable is 9 (nine) times of 1/4 wavelength long @ 14MHz....
Purfect for Field Day...

The calculations are in ./Windows/TDR.py (not ./Charts/TDR.py, that's what actually does the plotting)

Little discouraging, but I found the same "source code ".....
I also realized that , also little to late nanoVNASaver is "just the GUI" , but I had to start somewhere...
My next step is to find the actual TDR processing,,,
Maybe after I muddle thru the nanoVNASaver TDR undocumented / uncommented source code
( quite expected ) I will make (some) more progress.
BTW - for all those who keep telling me to "use S11 " phase reversal " - this TDR GUI does use S11 , so
it looks as TDR GUI is "just another layer" of software...

I am still in KISS mode - TDR in principle is
" start timer, then send a pulse and measure time when such pulse returns "
it cannot be much simpler,

As of today - I still do not know how nanoVNA generates such pulse and how "sweep" frequency (?) setup
is related to this simple principle of sending a pulse down the line.

PS
When this is all done I may break down and
open the RG6 I have
observe the dielectric - my guess it is poly-whatever
and actually use nanoVNA to measure the VF...

what a goal...

ah yes - my current cable is 9 (nine) times of 1/4 wavelength long @ 14MHz....
Purfect for Field Day...

We all have our favorites, mine is the SARK 100, got it from Amazon for around $50.

It has a bright backlit screen, apply 12v and you’re ready to go, in 30 seconds you have your SWR. Absolutely great in the field and since I use the same battery for my QCX-Mini not much extra to carry.

Yes, the VNA can be used quite well for this purpose but it’s no well suited for field work IMHO.

John
KK4ITX

Hi Fran?ois,

As an example, I routinely use a nanoVNA or antenna analyser to adjust my 136 and 475 kHz antennas at my home and remote QTH's, via a switch or PC-selected port which routes the antenna path to either the Class D/E amplifier or the analyser. To avoid the sort of trouble you correctly point out, activating the switch simultaneously disables the amplifier drive.

For my remote station, VK6MJM, I use a RigExpert AA-30.Zero "naked"analyser under station PC control, largely because I've not found any nanoVNA application reliable enough to connect faultlessly over long periods. The RigExpert Antscope software, although relatively basic, performs better in this regard. (The station is 300 km away).

I like your proverb: there's a near equivalent in English which talks about "casting pearls before swine" .

73, Peter.

On Thu, Jun 8, 2023 at 01:53 PM, Jim VE7RF wrote:


<Before the VNA was available, I would just measure the C between center conductor + braid. Knowing how many pf per foot the cable was, it's a simple math calculation for the physical length. Knowing the VF, the electrical length is also calculated.

This works very good on a known length of coax...dead on actually. On coax that you don't know how many pf per foot, cut exactly 1'-2'-3' of coax off the end of the run / roll...and measure it.

MFJ also has about 8 different antenna analyzers available, some analog and some digital.
Comet has very nice ones, too, for around $500.

NanoVNA is by far the cheapest, but comes with no instructions or documentation.
The NanoVNA-F has a different type of screen than the NanoVNA-H models, and it's screen is more visible when outdoors - but still not too good in the sun. I _really_ need a sunshade for it in Florida.

To get a 'feel' for using a nano, watch some youtube videos - there are many.
That might help for other analyzers too.
--
Doug, K8RFT

When you adjust a fan dipole trim the high frequency one first. Then the lower one, and
lower and so on. Look up G3BDQ's book on Practical Wire Antennas.

That's good, but anyway, even if the resonance has been found for each of the two frequencies (zero reactant), the radiation resistance will not be identical and neither will be 50 ?.

That's why I match the impedance with a double 'L' in the center of the antenna. Thus, at the two frequencies, the impedance will be 50 + j0 ?. As the double 'L' adapter can also compensate, if necessary, the reagent on each frequency it is not necessary to take the cabbage to cut the strands at the small onions (but it does not harm either) [se prendre le chou pour tailler les brins aux petits oignons] . With this system the antennas are not necessarily resonant but it is better to be close to them so as not to degrade performance. The reagent induces more important caurants which are useless but which produce losses; such as cos(phi) in electrical distribution.

We measure the S11 without the adapter with a nanoVNA, we calculate the adapter, we put it in place and, normally, that's 50+j0... if we're not mistaken.

73
--
F1AMM :)
Fran?ois

-----Message d'origine-----

De la part de F4WCV
Envoyé : samedi 10 juin 2023 09:12

When you adjust a fan dipole trim the high frequency one first. Then the lower one, and lower and so on. Look up G3BDQ's book on Practical Wire Antennas.

I mainly just want to use it to find the best position on my coil! Lol

Hello
Some OMs, in fact, temporarily replace their Tx with a nanoVNA to adjust their tuning box. You have to be careful that the TX does not end up in front of the NanoVNA.

In France we call that: giving jam to the pigs ("donner de la confiture aux cochons") :)
--
F1AMM
Fran?ois

De la part de Mike Anderson/KF?AWL
Envoyé : samedi 10 juin 2023 06:50

Hopefully, if we ignore you, you will stop your BS as you have done in other groups and just fade away.
We are willing to help those who are really wanting and needing it. Not those who spread crap like you have and do.
Also quit hiding behind, the "ANNE RANCH" BS. I have personally informed her of you using her name and causing trouble.
I am sure, she is going to be contacting you. You can not hide from her.
Clyde

I mainly just want to use it to find the best position on my coil! Lol
Its small a lot more portable then a mfj and affordable if it breaks in the field.
The stock owner manual goes way overboard with things for what I want lol

A NanoVNA calculates the SWR for you. If this SWR is so important for an OM at the output of its Tx, it is not a very relevant measurement produced by a NanoVNA.

SWR is a number and only *one*

A NanoVNA is a measuring device that allows you to measure a couple of *two* numbers as a function of frequency using only port 0. The NanaoVNA will present these two numbers to you in multiple forms adapted to a particular use. The two most important:
- The impedance in the form A+jB (A et B in ?)
- Parameter S11 in the form again a+jb

For example, if you notice that at the output of your Tx you have a high SWR, not very compatible with a Tx with transistors, what is relevant is to correct your installation to reduce this SWR. This SWR is the consequence of the fact that the impedance brought back by your antenna + the transmission line is not 50 + j0 or 50. You must correct your installation and the NanoVNA will help you calculate the device to be implemented.

A simple doublet resonating at the frequency of use never presents an impedance of 50. Do not stop at the evaluation of the SWR by your NanoVNA. The SWR is only a sterile observation.
--
F1AMM
Fran?ois

Thanks for trying to be a help brother. I watched both those videos before but something in them just didn't click.
I just sat down and read the beginner's guide start to finish and setting this one up is no different the the old one i had! Lol
I think trying to read the (official) factory guide get me all twisted up trying to follow it. Smh I bet tomorrow I have my antenna up and running finally ?

Mike,

I found these short videos very helpful for doing SWR readings on antennas.

How to read SWR on nanoVNA.


How to calibrate nanoVNA.

On 6/9/23 6:19 PM, Anne Ranch wrote:

On Fri, Jun 9, 2023 at 04:46 PM, Roger Need wrote:

The TDR feature in NanoVNA Saver has some issues

Allow me to discourage you from such posting... you will get crucified by "guardians of purity of nanoVNA" , but I assume you are an adult and can take it.
Yes, the nanoVNASaver is a challenge , to put it mildly. ( and I will leave it at that...)
I am still searching for a clue where to find at least some of the TDR code.
I got sidetracked actually calculating the REAL RG6 cable length to act as "in line transformer".
And it is too hot to work on the antenna....
-=-=

The calculations are in ./Windows/TDR.py (not ./Charts/TDR.py, that's what actually does the plotting)

It's pretty straightforward in function updateTDR() - blackman window, ifft, convolution with 1s to turn impulse response into step response, then calculate Z from the step response
self.step_response_Z = 50 * (1 + self.step_response) / (1 - self.step_response)


I posted the source snippet an hour or so ago.

The length you posted seems to be about right, if you had entered 0.66 for the VF and the RG-6 was actually foam dielectric with a VF of 0.84


__init__() sets up the defaults and populates the cable type dropdown with corresponding velocity factors.

the only tricky part is where it concatenates a series of smaller sweep segments.
s11 = []
for d in self.app.data11:
s11.append(np.complex(d.re, d.im))

app.data11 is a list of data sets.

One area where it could foul up is if the points aren't equally spaced, or if the segments have any overlap. The other place where a hiccup could occur is if there's a truncation issue in setting the frequencies of the segments. I've been bitten by that when trying to do log sweeps and the step size at the low end is < minimum step size.

On Fri, Jun 9, 2023 at 04:46 PM, Roger Need wrote:

The TDR feature in NanoVNA Saver has some issues

Allow me to discourage you from such posting... you will get crucified by "guardians of purity of nanoVNA" , but I assume you are an adult and can take it.
Yes, the nanoVNASaver is a challenge , to put it mildly. ( and I will leave it at that...)
I am still searching for a clue where to find at least some of the TDR code.
I got sidetracked actually calculating the REAL RG6 cable length to act as "in line transformer".
And it is too hot to work on the antenna....

On Fri, Jun 9, 2023 at 01:26 PM, Jim Lux wrote:

It's useful to know how to make the TDR work - I've found more than one
feedline problem by using TDR - yeah, sometimes if there's combinations
of solid, foam, and air dielectric, the distances don't work out, but
you can still see the discontinuities from connectors.

The TDR feature in NanoVNA Saver has some issues. In 5.5 it does not plot the time graph correctly. In all versions the impedance graph was not correct in the initial release and still has problems. I find doing TDR on the NanoVNA itself is easier and the NanoVNA app TDR display plots impedance much better. Take a look at the attached plots from a NanoVNA-H4 , NanoVNA App and Saver. The first scan is 25 feet (7.62 meters) of RG58 and the second is with 8 feet (2.4 meters) of RG6 added on the end. Nominal impedance of the RG58 is 50 ohms and the RG6 is 75. Note how NanoVNA App resolves the impedance of the two transmission lines

Roger

There is an Absolute Beginners Guide to the NanoVNA in the Files section of this group

/g/nanovna-users/files/Absolute%20Beginner%20Guide%20to%20The%20NanoVNA/Absolute_Beginner_Guide_NanoVNA_v1_6.pdf

Roger

I bought a NANO VNA when they first came out to use as a antenna analyzer. I sold it after I bought a regular analyzer and since bought another VNA
This is new updated software is confusing compared to the fist one I had ?
Trying to read the manual im getting more confused trying to figure out the basics of swr measurement. Can anyone give me a dumbed down step by step version how to set the new software for SWR?
It would be much appreciated ?