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added a bluetooth module

H / H4 / LiteVNA allow install Bluetooth or WiFi to serial module (deivices have internal serial connection pins) for use wireless connect.
I test bluetooth HC-05, HC-06 moduless (maximum speed depend from module revision) and get up to 460800 baudrate.

PS wireless communication increases measurement noise, especially WiFi

On Sat, Jun 10, 2023 at 11:16 AM, Siegfried Jackstien wrote:

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

A few years ago, before the nanovna, I bought the MINI60 version of the Sark.
It's very small, it sweeps the band you choose, shows the frequency of minimum SWR but you can also read each measurement of the sweep. Mine has the built-in bluetooth module, and works with my Android phone. And it IS readable in sunlight!
They currently cost around $120, though. About the price of the nanovna-h4 or -F.
It's in my Harbor Freight plastic "ammo box" case with the Nanos and an MFJ-207 analyzer. I am still glad to have it.
--
Doug, K8RFT

On 6/10/23 7:34 PM, Jim Shorney wrote:

The wayback machine has it.

The 39B2 link below the text leads to a PDF.
73
-Jim
NU0C

foam, 82% VF

The wayback machine has it.



The 39B2 link below the text leads to a PDF.

73

-Jim
NU0C

On Sat, 10 Jun 2023 13:07:27 -0700
"Anne Ranch" <anneranch2442@...> wrote:

I did ask Mts Goggle and got no (real) answer

Here is the label on the cable

Eagle Aspen 39B2 RG-6 2.25 GHz Digital Coaxial Cable, 6FT, Black, High Performance 2.25 GHz CMX 18AWG 75°C UL E227171

Please share if you know the velocity factor - VF .

Thanks

On 6/10/23 1:07 PM, Anne Ranch wrote:

I did ask Mts Goggle and got no (real) answer
Here is the label on the cable
Eagle Aspen 39B2 RG-6 2.25 GHz Digital Coaxial Cable, 6FT, Black, High Performance 2.25 GHz CMX 18AWG 75°C UL E227171
Please share if you know the velocity factor - VF .

You might be able to figure it out from the 18 AWG (which is the diameter of the center conductor). The Z depends on the ratio of inner to outer diameter AND the epsilon of the dielectric.

OTOH, who's to say that the center conductor really is 18 AWG.

You might also be able to figure it out from the loss vs frequency.

Or, perhaps, the mfr's website (which doesn't seem to go anywhere.. they may be out of business?)

Since I saw some google references to it being used for satellite TV, I'm going to guess it's foam dielectric. Lower dielectric losses for higher frequencies.

But testing a sample is the only way you'll know, if you can't get the mfr data sheet.

If you have a sample and you cut it open, you'll know. foam looks different than solid.

How long is it?

Can you measure how long it is, then use the nano to see how long "Electrically" it is,
and there ya go you got it's VF.

Joe WB9SBD
.

A Contest 40 Years in The Making!
<>
MAIDENHEAD MAYHEM

On Sat, Jun 10, 2023 at 01:07 PM, Anne Ranch wrote:

Eagle Aspen 39B2 RG-6 2.25 GHz Digital Coaxial Cable, 6FT, Black, High
Performance 2.25 GHz CMX 18AWG 75°C UL E227171

Please share if you know the velocity factor - VF .

It is foam dielectric with VF of 82%

Roger

I am not sure I have another scrap cable I can take apart, This one has been given to me and I do not have same crimp connector to cut / restore it.

Is there any way to tell if the dielectric is PE or foam?

73,
Joseph W6JHP

I did ask Mts Goggle and got no (real) answer

Here is the label on the cable

Eagle Aspen 39B2 RG-6 2.25 GHz Digital Coaxial Cable, 6FT, Black, High Performance 2.25 GHz CMX 18AWG 75°C UL E227171

Please share if you know the velocity factor - VF .

Thanks

Sigi:

Did you write anything up or have pictures of your Bluetooth add-on.

I’d like to give it a try.

Thanks

Ed McCann
AG6CX

On 6/10/23 11:22 AM, Anne Ranch wrote:

Jim Lux,
as always, your replies are clearing few of mine misconceptions, thanks.
With all this FFT (frequency to pulse and time ) it is still unclear how CHANGING the "sweep" changes the "estimated cable length".
...and how it still "calculates" the cable length AFTER it is hooked to the actual load / antenna (variable with frequency ) - assuming that TDR can be calculated from open , shorted and "real terminated" but unknown and variable with frequency termination.

The open/short/load just makes sure the reflection measurement is correct. It has nothing to do with the actual measurement of a feedline.

The reason you can "see" connectors and the antenna in the TDR is that they are not exactly the same impedance, so you see the discontinuity. If you had a single length of coax, and a load that was well matched to the coax, you probably wouldn't be able to measure the length.

Think of it as estimating the size of a room with your eyes closed by listening how long it takes for the echo to come back when you clap your hands. Easy in a boxlike room with hard walls. Impossible in an acoustically dead room, because the sound just goes out and is absorbed.

It is the rare antenna that is matched at all frequencies. So even it's a good match (and has no reflection) at a few frequencies, for most of the other frequencies, it reflects back significant energy. And that's enough to make the TDR work.

To kind of use a different conceptual view, imagine that you measure the phase shift (and ignore amplitude) for a series of frequencies. You plot those on a graph (unwrapping where needed), and then fit a straight line to the points. The slope of that line corresponds to the length of the cable. And even if there's some missing points (because the amplitude is small where the antenna is well matched) you can still fit the line. So you get a more accurate measurement - sort of like averaging.

The cool thing about the FFT approach or the "fit a straight line" (versus the "look for zero or 180 phase in the reflection and it's a multiple of 1/4 wavelength" ) is that it combines multiple measurements into what you want - the delta phase vs delta frequency. (FWIW, Delta phase/delta frequency is "group delay")

It also lets you know if you're measuring something that's dispersive (where the delay varies with frequency), because then, the plot of phase vs frequency won't be a straight line. That's important for things like waveguides, ionized media, traveling wave tube amplifiers, etc - because a group delay that's not flat means that pulsed waveforms will be distorted.

With real load connected the calculation must include "real load" somehow...

On 6/10/23 11:04 AM, Roger Need via groups.io wrote:

Those interested in how the TDR was implemented in NanoVNA Saver will find the details in this groups.io post by Herb Walker.
/g/nanovna-users/message/9651
For more details on how the S11/IFFT method of TDR works this tutorial by Agilent is quite informative. It includes details on why "windowing" the data is necessary, how to determine the upper stop frequency required based on estimated cable length, why the lower start frequency should be close to DC and other considerations.

Roger

The Keysight Ap Note is a good reference.

For what it's worth, in the older NanoVNA-Saver version I have, there are some problems in the implementation, specifically because it does not deal with the "non zero" starting frequency. If you set 10 MHz to 60 MHz sweep, I don't know that you'd get the right results, because it just assumes that you're feeding the IFFT evenly spaced points from 0-{highest freq}.

It is possible that when you select TDR mode it changes how it builds the measurement segments so that the lowest frequency is equal to the spacing between frequencies, and then puts in a zero for the DC term.

I do know that the Keysight boxes (e.g. the fieldfox) do handle both lowpass and bandpass correctly. When you pay $20k, that's something you get. For other applications, with uneven spacing, I've written code to deal with it.

Jim Lux,
as always, your replies are clearing few of mine misconceptions, thanks.
With all this FFT (frequency to pulse and time ) it is still unclear how CHANGING the "sweep" changes the "estimated cable length".

...and how it still "calculates" the cable length AFTER it is hooked to the actual load / antenna (variable with frequency ) - assuming that TDR can be calculated from open , shorted and "real terminated" but unknown and variable with frequency termination.

With real load connected the calculation must include "real load" somehow...

Those interested in how the TDR was implemented in NanoVNA Saver will find the details in this groups.io post by Herb Walker.

/g/nanovna-users/message/9651

For more details on how the S11/IFFT method of TDR works this tutorial by Agilent is quite informative. It includes details on why "windowing" the data is necessary, how to determine the upper stop frequency required based on estimated cable length, why the lower start frequency should be close to DC and other considerations.



Roger

Jim Lux,

That was a well written explanation of how "TDR" is done in the NanoVNA. Thanks for taking the time to write it up.

Roger

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