开云体育

Hi, Jesper,
Before You start working with NanoVNA and Joe's SW, take a look at this thread and the following discussion


--
Alex

Jim, I was working for HP when Tektronix loaned us one of their early
engineering models of their FFT'ed spectrum analyzer. They just requested
we document what we found. Well,..... it was OK on discrete single-signal
inputs, but,....... with digitally modulated signals, it severely aliased
throughout its RF range. We assured there was no overload and that we were
operating it well below anything that might have influenced its behavior.
A month later, we gave it back to Tek with only one comment - that which I
have related. As far as application with digital circuitry and equipment,
it was useless.

Dave - W?LEV

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

On 2/26/22 8:54 AM, Jim Lux wrote:

Attached are a couple plots of the processed digital output of an ADC, where there was leakage of an external clock signal into the system.? Sample rate is about 49.2 MHz, interference signal is 66 MHz, Signal being digitized is ~110 MHz (aliased down to about 12 MHz) - 12 bit ADC

You can see that there's really no direct sign of the 66 MHz in the output (e.g. 66 MHz would have aliased to 1.34 MHz), but there's plenty of IMD with the interaction of the 66MHz and the 110 MHz/12 MHz input

Excuse me - 66 MHz aliases to 16.8 MHz ( 66/49.2 = 1.34 - 1 = 0.34 * 49.2 = 16.8)? - Too early in the morning.

Attached are a couple plots of the processed digital output of an ADC, where there was leakage of an external clock signal into the system.? Sample rate is about 49.2 MHz, interference signal is 66 MHz, Signal being digitized is ~110 MHz (aliased down to about 12 MHz) - 12 bit ADC

You can see that there's really no direct sign of the 66 MHz in the output (e.g. 66 MHz would have aliased to 1.34 MHz), but there's plenty of IMD with the interaction of the 66MHz and the 110 MHz/12 MHz input

On 2/25/22 8:39 AM, moensted1@... wrote:

@ Jim Lux:

So the idea is to feed a test signal (not from the VNA) into the ADC, and use the VNA to inject power supply noise into the system, and then measure the effect? Since the VNA is analog out and analog in, you'd run an ADC/DAC back to back, and use the DAC output to feed the VNA's receiver port.

To be honest, the way I've done this is by processing the digitized samples offline, and using a nice pure sinewave as the test signal into the ADC. If you want to do it in the analog domain, then a spectrum analyzer might be a better "readout" device. <<

No, it actually is to feed the output from the VNA into the PDN / supply decoupling network e.g. of a DAC while the DAC is powered on but not receiving data or clock signals. Joe Smith outlines how the part with a powered-up device can be done in his video on youtube. Thus the intrinsic capacitances/inductances/resistances of the DAC PSU pins may be measured together with the decoupling capacitors. However, I am unsure of the effect that the square wave from the nanoVNA will have .. ? Will it perturb into the DAC's circuitries and confuse matters - or will it reliably give a good impression of the PDN + DAC impedance network?

I hope this clarifies things (and thanks again for considering and replying ;-))?

Right, so CH0 of the VNA connects to the DAC power (through some coupling network). And then you'd hook the output of the DAC to CH1 (through some coupling network to block DC).? And you'd directly measure the Power Supply rejection.

Yeah, that might work.

What that would catch is any harmonic distortion caused by the interference (since the VNA is only looking at the stimulus frequency).? The typical problem with data converters and poor decoupling is that you get an interaction between the sample rate and the spurious signal (often clock noise at a different frequency) and the desired signal.? The VNA won't find that.? A spectrum analyzer would.

Looking at it the other direction (with ADCs) you put in a very clean sinewave at f1 and a small ripple on the power supply at f2, and sample clock f3. When you collect a bunch of samples and then look at the power spectrum, you'll see not only f1 (as expected), and f2 (maybe), but you also see f1+f2 or f1-f2 (and all the possible multiples, really n*f1 +/- m*f2), as well as combinations of f2,f3 and f1.? I had this specific problem with a ADC running at 50 MHz sample rate and 66 MHz from the CPU clock leaking in on the power supply. With an input signal at 12 MHz, you'd see other spurs.

On a DAC (i've never tried this) you would put a sequence into the DAC expected to generate a particular frequency f1.? Then you'd inject f2 into the power (or clock) as an interferer, and look at the analog spectrum output to see if there's anything other than f1, f1+/-fs, etc.? I suppose you could do it with a DAC putting out DC (fixed input code), but the leakage effects there are likely to be different than in the dynamic case. (Unless the DAC is something where it's basically providing a DC setpoint, say as electronic frequency control to a TCXO, in which case the interference would show up as FM or PM on the TCXO output)

@ Jim Lux:

So the idea is to feed a test signal (not from the VNA) into the ADC, and use the VNA to inject power supply noise into the system, and then measure the effect? Since the VNA is analog out and analog in, you'd run an ADC/DAC back to back, and use the DAC output to feed the VNA's receiver port.

To be honest, the way I've done this is by processing the digitized samples offline, and using a nice pure sinewave as the test signal into the ADC. If you want to do it in the analog domain, then a spectrum analyzer might be a better "readout" device. <<

No, it actually is to feed the output from the VNA into the PDN / supply decoupling network e.g. of a DAC while the DAC is powered on but not receiving data or clock signals. Joe Smith outlines how the part with a powered-up device can be done in his video on youtube. Thus the intrinsic capacitances/inductances/resistances of the DAC PSU pins may be measured together with the decoupling capacitors. However, I am unsure of the effect that the square wave from the nanoVNA will have .. ? Will it perturb into the DAC's circuitries and confuse matters - or will it reliably give a good impression of the PDN + DAC impedance network?

I hope this clarifies things (and thanks again for considering and replying ;-))?

Cheers,

Jesper

On 2/25/22 7:48 AM, moensted1@... wrote:

Hi all - & thanks very much for your prompt replies!

@Jim Lux:

Also, bear in mind that the stimulus on the NanoVNAs is a square-ish wave, not a nice clean sine wave with low distortion and spurs. <<

.. Hmmm, yes, I am aware of this, however, I just do not know how it will affect the circuitry in question, so I thought I'd give it a chance. But maybe you have experiences with this already?

Gotcha - that's kind of what I thought, but the OP mentioned ADCs and DACs. And that is a different kettle of fish, measurement wise. <<

.. What I would like to be able to measure impedance/frequency-wise is the interaction between the decoupling capacitors and the DAC or ADC and the placement of Vias etc. I can simulate this to some extent but not having expensive software available I cannot be absolutely sure these simulations are correct. And then - as I understand it - there may also be "hidden" internal decoupling capacitances in the DAC/ADCs that may alter the response of the DAC/ADC PSU pin responses .. So it just would be great to be able to verify things by measurement - that is also not too expensive.

So the idea is to feed a test signal (not from the VNA) into the ADC, and use the VNA to inject power supply noise into the system, and then measure the effect?? Since the VNA is analog out and analog in, you'd run an ADC/DAC back to back, and use the DAC output to feed the VNA's receiver port.

To be honest, the way I've done this is by processing the digitized samples offline, and using a nice pure sinewave as the test signal into the ADC. If you want to do it in the analog domain, then a spectrum analyzer might be a better "readout" device.

@AlexSpb:

Regarding "original NanoVNA", I just have purchased one of the cheap clones from AliExpress, that are still available. <<

Ok, great! Any chance you have a link to the one you bought? Might it be identical to this one: ... apparently this is a "Hugen" version but if I am not mistaken these "H" versions are exactly the ones Joe mentions in the video may have firmware errors ... ? But maybe this is corrected with:

Then just flashed it with the recommended FW version from Joe's git repo. << ...

Well, admittedly I am not a programmer so I hope I can also ask you to verify that you downloaded this software: nanoVNA_original_2p10.zip from the link below?



Or is there some other software that I am missing here?

I'd appreciate your feedbacks - new to this so insights are really appreciated ;-)

Cheers & thanks,

Jesper

Hi all - & thanks very much for your prompt replies!

@Jim Lux:

Also, bear in mind that the stimulus on the NanoVNAs is a square-ish wave, not a nice clean sine wave with low distortion and spurs. <<

.. Hmmm, yes, I am aware of this, however, I just do not know how it will affect the circuitry in question, so I thought I'd give it a chance. But maybe you have experiences with this already?

Gotcha - that's kind of what I thought, but the OP mentioned ADCs and DACs. And that is a different kettle of fish, measurement wise. <<

.. What I would like to be able to measure impedance/frequency-wise is the interaction between the decoupling capacitors and the DAC or ADC and the placement of Vias etc. I can simulate this to some extent but not having expensive software available I cannot be absolutely sure these simulations are correct. And then - as I understand it - there may also be "hidden" internal decoupling capacitances in the DAC/ADCs that may alter the response of the DAC/ADC PSU pin responses .. So it just would be great to be able to verify things by measurement - that is also not too expensive.

@AlexSpb:

Regarding "original NanoVNA", I just have purchased one of the cheap clones from AliExpress, that are still available. <<

Ok, great! Any chance you have a link to the one you bought? Might it be identical to this one: ... apparently this is a "Hugen" version but if I am not mistaken these "H" versions are exactly the ones Joe mentions in the video may have firmware errors ... ? But maybe this is corrected with:

Then just flashed it with the recommended FW version from Joe's git repo. << ...

Well, admittedly I am not a programmer so I hope I can also ask you to verify that you downloaded this software: nanoVNA_original_2p10.zip from the link below?



Or is there some other software that I am missing here?

I'd appreciate your feedbacks - new to this so insights are really appreciated ;-)

Cheers & thanks,

Jesper

On 2/25/22 6:38 AM, AlexSpb wrote:

PDN means "power distribution networks", an odd term that had appeared for those low-Z nets of filtering MLCC caps in power rails, etc. ))
All this nets are characterized by very low Z at low frequency band starting from DC to a couple of MHz.

Gotcha - that's kind of what I thought, but the OP mentioned ADCs and DACs.? And that is a different kettle of fish, measurement wise.

Regarding "original NanoVNA", I just have purchased one of the cheap clones from AliExpress, that are still available.
Then just flashed it with the recommended FW version from Joe's git repo.

PDN means "power distribution networks", an odd term that had appeared for those low-Z nets of filtering MLCC caps in power rails, etc. ))
All this nets are characterized by very low Z at low frequency band starting from DC to a couple of MHz.

Regarding "original NanoVNA", I just have purchased one of the cheap clones from AliExpress, that are still available.
Then just flashed it with the recommended FW version from Joe's git repo.
--
Alex

You may try Walmart online, they have one that is close to the original for
$20+ bucks.

On Fri, Feb 25, 2022 at 9:11 AM <moensted1@...> wrote:

Hi nanoVNA users,

This is my first post here so I hope I am posting in the right topic
subgroup .. ?

My reason for posting is that I am interested in buying and getting to
know how to use a nanoVNA for PDN measurements (DACs and ADCs) and passive
component characterization. To this end I have watched this video by Joe
Smith:




and it looks very much as if his software may do exactly what I need a
software to do. However, in the intro to the video at appr. 2:15 mins he
compares the capabilities of various nanoVNAs and apparently it is
specifically the "original VNA" - shown at 2:15 mins - that has both a low
lower cut-off frequency (10 kHz), a wide dynamic range, and works in a way
that is fully compatible with his software.

Having searched e.g. ebay for an "original" nanoVNA I get like hundreds of
"hits" and I don't really know what to go for ... ??

Might one of you here know which nanoVNA Joe Smith uses and where it can
be bought (if possible it would be preferable within the EU)? Help would be
much appreciated :-)

Cheers & thanks for considering,

Jesper M





--

Clear Skies and
Keep Looking up
David Stansberry

On 2/25/22 6:08 AM, moensted1@... wrote:

Hi nanoVNA users,

This is my first post here so I hope I am posting in the right topic subgroup .. ?

My reason for posting is that I am interested in buying and getting to know how to use a nanoVNA for PDN measurements (DACs and ADCs)

PDN measurements? What does PDN stand for?

and passive component characterization. To this end I have watched this video by Joe Smith:



and it looks very much as if his software may do exactly what I need a software to do. However, in the intro to the video at appr. 2:15 mins he compares the capabilities of various nanoVNAs and apparently it is specifically the "original VNA" - shown at 2:15 mins - that has both a low lower cut-off frequency (10 kHz), a wide dynamic range, and works in a way that is fully compatible with his software.

I'd be careful about performance down low (10kHz) - While the VNA may generate the frequencies, there is AC coupling at various places in the analog chain, and, of course, the "detection" frequency is 5kHz (that is, the receivers use an LO that is 5kHz away) so I'd be careful about mixer performance where the RF, IF, and LO are all close together. Sure, the SA612 probably works down to DC, but...

Also, bear in mind that the stimulus on the NanoVNAs is a square-ish wave, not a nice clean sine wave with low distortion and spurs.

Hi nanoVNA users,

This is my first post here so I hope I am posting in the right topic subgroup .. ?

My reason for posting is that I am interested in buying and getting to know how to use a nanoVNA for PDN measurements (DACs and ADCs) and passive component characterization. To this end I have watched this video by Joe Smith:



and it looks very much as if his software may do exactly what I need a software to do. However, in the intro to the video at appr. 2:15 mins he compares the capabilities of various nanoVNAs and apparently it is specifically the "original VNA" - shown at 2:15 mins - that has both a low lower cut-off frequency (10 kHz), a wide dynamic range, and works in a way that is fully compatible with his software.

Having searched e.g. ebay for an "original" nanoVNA I get like hundreds of "hits" and I don't really know what to go for ... ??

Might one of you here know which nanoVNA Joe Smith uses and where it can be bought (if possible it would be preferable within the EU)? Help would be much appreciated :-)

Cheers & thanks for considering,

Jesper M

discussion about VNA calibration error models:
/g/nanovna-users/topic/34237712

This paper seems directly related to the Unknown Through Calibration error model, as I understand:


--
Alex

Hi,
some related papers from net search,


There had been a discussion thread in this group with recent ly added related paper, too
--
Alex

It's not mine but I do share the sentiment ;)

I've been retired for 18 years and even I DON'T have that much time, wow, I hope you have a day job. Very nice work though.

Mike C.

Maybe of help:
(source code on github).

On Thu, 24 Feb 2022 at 23:38, James F 2E0KVS <fletchersjames@...>
wrote:

Hi all,

I am currently working on implementing various VNA calibration algorithms
in MATLAB. I have succesfully implemented SOLT and one-port algorithms, but
I am having trouble getting my head around the unknown thru/8 term 2-port
calibration model. I've been basing my work off the following document by
Doug Rytting

, which has been very useful. I'm currently trying to use page 23+24 of
this document to build my unknown thru calibration algorithm, but I'm
uncertain how I can produce the error terms needed for the constant k.

I would greatly appreciate any help, or links that may prove useful.

James G8YYH/2E0KVS

Hi all,

I am currently working on implementing various VNA calibration algorithms in MATLAB. I have succesfully implemented SOLT and one-port algorithms, but I am having trouble getting my head around the unknown thru/8 term 2-port calibration model. I've been basing my work off the following document by Doug Rytting , which has been very useful. I'm currently trying to use page 23+24 of this document to build my unknown thru calibration algorithm, but I'm uncertain how I can produce the error terms needed for the constant k.

I would greatly appreciate any help, or links that may prove useful.

James G8YYH/2E0KVS

You needed to sweep up to a higher frequency to see your impedance null.

A method to calculate the VF of any feedline, that will work with a VNA, antenna analyze or SWR bridge.
(this sounds complicated, but only takes a minute to do if you have already measured the actual feedline length):

Leave one end of the feed line open (or shorted -not terminated with the characteristic impedance).
Sweep over a wide frequency range, starting with a bit lower than MHz=150/(feedline length in meters),
and stopping after 2 (preferably 4) multiples of the starting frequency.

Carefully note the frequencies where you get a peak and a null.
You need to sweep a wide enough frequency range to to get at least two peaks or two nulls.
It will be apparent from the frequencies recorded, which is the fundamental, 2nd harmonic, etc.
Calculate the free-space length (meters) using 299.8/(2 x frequency x harmonic).
Your actual length / (calculated free-space length) is the exact velocity factor.

VF can vary 1 percent between batches of the same type coax, less so for parallel line.
I used this technique to get the exact VF of a 500 foot length of LMR400,
and knowing this was later able to locate a center conductor break with 1/8 inch accuracy.
--
N0YWB