开云体育

Thanks, Jim. I'll read the analysis.

I didn't realize the ADC was 16 bits. That's a lot. Now I feel even less forgiving about the observed performance.

I don't understand why the possible imperfections in the load you postulate matter. Shouldn't calibration nullify them?

Brian

On 2/6/23 1:33 PM, Brian Beezley wrote:

That's an interesting idea, Dave. The LF spike is indeed at 60 kHz. However, N6LF is in Oregon. I would not expect WWVB to be that strong there. When connecting the VNA to a ground probe, occasionally he sees a spike from a 50 kW local AM station at 1.12 MHz.
My main concern is the resistive offset from 50 ohms and the climb in reactance at LF. I would think the NanoVNA has plenty of accuracy to nullify any such aberrations, but I don't know the details of its internal resolution or processing.

The measurements are made by integrating over 1 millisecond, after a I/Q conversion to 5kHz. It's a 16 bit ADC, but the noise floor isn't quite that good, and there's system noise too.


I started a formal analysis last summer but never finished.

1 part in 5000 is ~70 dB (20 log10(5000) = 74 dB)

The trace noise is bigger than that.

On 2/6/23 11:36 AM, Brian Beezley wrote:

N6LF has been trying to calibrate his NanoVNA-H4 through a wideband balun for common-mode current suppression when measuring an open wire line ground probe. He has had perplexing results. As a test he tried paralleling two 50-ohm loads, calibrating the VNA with that load, and then measuring it. He did not disconnect/reconnect the load and he measured it immediately after calibrating. He got the results depicted in the plots.
Resistance is off 1 part in 5000 and reactance has an upward creep at LF of more than that. Spikes occur. Are these results reasonable?

1 in 5000 is actually pretty good. That's 0.02% - I doubt the load is known that accurately over that bandwidth.

Similarly, the reactance of the load is probably not zero. 0.1 ohms at 50 kHz is about 0.3 uH. That's the inductance of about a foot of wire. And with the falling reactance with rising frequency, maybe there's a parasitic L and C. (or an offset in the calibration)

That's an interesting idea, Dave. The LF spike is indeed at 60 kHz. However, N6LF is in Oregon. I would not expect WWVB to be that strong there. When connecting the VNA to a ground probe, occasionally he sees a spike from a 50 kW local AM station at 1.12 MHz.

My main concern is the resistive offset from 50 ohms and the climb in reactance at LF. I would think the NanoVNA has plenty of accuracy to nullify any such aberrations, but I don't know the details of its internal resolution or processing.

Brian

The spike at the extreme left could be WWVB at 60 kHz. Have no idea what
the spike at 1.8 MHz might be.

Dave - W?LEV

--
Dave - W?LEV

N6LF has been trying to calibrate his NanoVNA-H4 through a wideband balun for common-mode current suppression when measuring an open wire line ground probe. He has had perplexing results. As a test he tried paralleling two 50-ohm loads, calibrating the VNA with that load, and then measuring it. He did not disconnect/reconnect the load and he measured it immediately after calibrating. He got the results depicted in the plots.

Resistance is off 1 part in 5000 and reactance has an upward creep at LF of more than that. Spikes occur. Are these results reasonable?

Brian

On 2/6/23 10:14 AM, Larry McElhiney via groups.io wrote:

The boards use three terminal ceramic filters for Bandpass. (Really only two terminal, but can be installed without regard to “polarity”.
They are actually ceramic resonators and sell for about 10-15 cents apiece from China.
Since the evaluation boards have been sold for as low as $8.00, the manufacturers will use low cost components.

Anyone have a part number? Usually, the data sheet will show S21 and S11.

The boards use three terminal ceramic filters for Bandpass. (Really only two terminal, but can be installed without regard to “polarity”.

They are actually ceramic resonators and sell for about 10-15 cents apiece from China.

Since the evaluation boards have been sold for as low as $8.00, the manufacturers will use low cost components.

Larry
AC9OX

On 2/6/23 9:26 AM, PDXer wrote:

That would likely be the S11 magnitude - in the passband, the filter
lets the RF through, so it sees the 50 ohms on the other side, so
reflected power is small (i.e. good match). Outside the passband, the
filter probably reflects the power back, so S11 is close to 1.

S21 should show the bandpass characteristic (i.e. small magnitude (large
negative dB) outside the passband and big magnitude (small negative dB))
inside the passband.

Do you set the frequency range say from 20 Mhz to 50 Mhz, and set the centre frequency to 30 Mhz, and then sweep the frequency to get the graph?
What about SPAN and RBW (band width) - what do you set it to?
And it is set to read LOGMAG of S21?
What is supposed to happen on S11?

It occurs to me (after looking at some pictures of the test board)) that they might have just put something like a 10.7 MHz IF filter on the board.

Here's an example of such a filter, from Minicircuits.com




the first plot is S21, the second is S11

here's another one:

On 2/6/23 9:26 AM, PDXer wrote:

That would likely be the S11 magnitude - in the passband, the filter
lets the RF through, so it sees the 50 ohms on the other side, so
reflected power is small (i.e. good match). Outside the passband, the
filter probably reflects the power back, so S11 is close to 1.

S21 should show the bandpass characteristic (i.e. small magnitude (large
negative dB) outside the passband and big magnitude (small negative dB))
inside the passband.

Do you set the frequency range say from 20 Mhz to 50 Mhz, and set the centre frequency to 30 Mhz, and then sweep the frequency to get the graph?
What about SPAN and RBW (band width) - what do you set it to?
And it is set to read LOGMAG of S21?
What is supposed to happen on S11?

I couldn't find a schematic for the test board, so I don't know what the BPF looks like.

Span is just the size of the sweep - either you set start and stop, or set center and span.

RBW leave at the default - it doesn't make any difference.

What I'd expect on logmag S21 is that you see the bandpass characteristic of the filter.
What I'd expect on logmag S11 is that you see the input return loss, typically sort of the inverse of the bandpass, but often, you can see the individual sections of the filter.

If I can find a schematic, I can simulate it.

If you're using Windows, you might try getting a copy of Elsie from Tonne Software. The student version is free, and it lets you build filters of various kinds, either from specs, or by knowing the component values, and it can give you plots of S21 and S11 (and lots of others)).

Elsie and a VNA is a great pair. You can design in Elsie, build the filter on a board, then sweep it with the VNA.

If you want real fun (?) you can build a 3 section LC filter with variable L or C, and use the VNA to tune it. (which is more art than science, btw) It's a LOT easier than, say, tuning the cans on a diplexer, because your run of the mill LC will have lower Q.

That would likely be the S11 magnitude - in the passband, the filter
lets the RF through, so it sees the 50 ohms on the other side, so
reflected power is small (i.e. good match). Outside the passband, the
filter probably reflects the power back, so S11 is close to 1.

S21 should show the bandpass characteristic (i.e. small magnitude (large
negative dB) outside the passband and big magnitude (small negative dB))
inside the passband.

Do you set the frequency range say from 20 Mhz to 50 Mhz, and set the centre frequency to 30 Mhz, and then sweep the frequency to get the graph?
What about SPAN and RBW (band width) - what do you set it to?
And it is set to read LOGMAG of S21?
What is supposed to happen on S11?

On 2/5/23 12:36 PM, PDXer wrote:

I received the RF Demo kit for NanoVNA. The cables are indeed fiddly to attach on the pcb board, but I am getting used to it. Just hope that it will last for some long time rather than get mangled, and ruin my investment for the learning.
Anyhow I got it to calibrate OK for Open, Short and Load with the Demo Kit board and supplied cables.
But when I tried to read for the 30Mhz Band Pass Filter, the readings on the screen didn't come out what is indicated on the board. It was more squiggly curve type graphs on the display. I tried to change the settings with the SPAN and SCALE in the menu, but it made it actually worse or was just showing straight horizontal line.
Could someone please explain, what settings the VNA must have to display nice sharp dip of the graph as on the board?

That would likely be the S11 magnitude - in the passband, the filter lets the RF through, so it sees the 50 ohms on the other side, so reflected power is small (i.e. good match). Outside the passband, the filter probably reflects the power back, so S11 is close to 1.

S21 should show the bandpass characteristic (i.e. small magnitude (large negative dB) outside the passband and big magnitude (small negative dB)) inside the passband.

Greetings, The open, Short, Load calibration is fine for single port measurement. However,?there are two additional calibrations to be completed when you intend to perform two port?measurements. There is the isolation which is sometimes done just leaving both ports open.I have also seen where it is suggested to put 50 ohm calibration loads on both s11 and s21(if you have them). Last is Thru (you probably have that on your test board) If not, you can?just use a jumper from S11 to S21 for the calibration. This is my two cents worth, others may?wish to comment further.Good Luck73

I received the RF Demo kit for NanoVNA. The cables are indeed fiddly to attach on the pcb board, but I am getting used to it. Just hope that it will last for some long time rather than get mangled, and ruin my investment for the learning.

Anyhow I got it to calibrate OK for Open, Short and Load with the Demo Kit board and supplied cables.

But when I tried to read for the 30Mhz Band Pass Filter, the readings on the screen didn't come out what is indicated on the board. It was more squiggly curve type graphs on the display. I tried to change the settings with the SPAN and SCALE in the menu, but it made it actually worse or was just showing straight horizontal line.

Could someone please explain, what settings the VNA must have to display nice sharp dip of the graph as on the board? What am I doing wrong. I understand the RF board is showing how the band pass filter on the board is blocking the all other frequencies and only letting in 30Mhz in the filter? What should be the settings in the menu of the VNA? Thanks

Hi Chris,

1. Have you ensured USB OTG is turned on?
2. Have you tried connecting a USB storage device and seeing if it is
detected properly? To confirm it's usb data pins are intact? Have you tried
turning the usb-c connector upside down?
3. Have you tried a hard reset (this will delete everything from the
device)?

Best,

John



Op zo 5 feb. 2023 om 07:15 schreef Chris VK5SA <chris@...>:

On 2/5/23 12:55 AM, Steve wrote:

Hi all you experts! Just trying to use my older nanoVNA-H- ver. 0.2.3-1- for the first time and thought I'd update the FW before I got going. I'm not a computer guy, but believe, using the Absolute Beginners Guide, that I have downloaded and installed the DfuSe drivers and program properly (~3 hours!). My device manager doesn't seem to see the STM in DFU mode in the USB controller area. It does see the STM....Virtual COM port when in the regular mode and not in the DFU mode- just no joy in the USB controller area. So when I bring up the DfuSe software, there is no STM device shown. Any ideas where I'm going wrong? Thanks, Aloha, Steve

Is there a particular reason you're upgrading the firmware? I'd see if the unit will make the measurements you want with the existing firmware.

Hook it up to your PC and use one of the PC applications to control it, etc.

That way you'll know for sure that the cable works, for instance.

Steve,
If the defuse demo installation lasted for so long, you may need help to you someone on the spot.
You can view the process description from a different perspective on my website

There are several options to resolve the error.
This is a prerequisite for putting Nanovna in DFU mode before and plugging on the USB.
Sometimes USB3 does not recognize, look for USB2.
If I write a lot of opportunities, you will definitely get lost.
That's it for now.

--
Gyula HA3HZ ( )

Hi all you experts! Just trying to use my older nanoVNA-H- ver. 0.2.3-1- for the first time and thought I'd update the FW before I got going. I'm not a computer guy, but believe, using the Absolute Beginners Guide, that I have downloaded and installed the DfuSe drivers and program properly (~3 hours!). My device manager doesn't seem to see the STM in DFU mode in the USB controller area. It does see the STM....Virtual COM port when in the regular mode and not in the DFU mode- just no joy in the USB controller area. So when I bring up the DfuSe software, there is no STM device shown. Any ideas where I'm going wrong? Thanks, Aloha, Steve

On Sat, Feb 4, 2023 at 03:54 AM, John Simons wrote:

Which phone (make and model)? Which Android version?

Hi, John.

Oppo A52
v11

Chris VK5SA

Thanks, Gyula - Chris