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LabView Nano VNA hangs up on low number of sweep points


John Galbreath 2021/09/24 20:41

I am running TDR on LabView NanoVNA Windows 10 PC system.  No problem at all with default 100 points, but as I reduce the number of points (increase step size), the PC will ignore my mouse click (attempts to go from main to advanced, from smith chart to reflection coefficient, or simply turning sweep on/off).  It is as if the system is bogged down with processing data that it is too busy to respond to user commands.

It is necessary to increase step size to reduce the range and increase the resolution.  You can see from the attached plots that much more resolution is needed, but the system goes on strike.

My NanoVNA is a clone: ( a S-A-A-2N)  however it has behaved well so far.

Joe Smith 2021/09/25 01:15

This is by design.  It would be easy to throttle the update rate but as I mentioned, as a rule I don't limit limit what the user does with the software.

Joe Smith 2021/09/25 10:40

My current PC is over 5 years old and due for an upgrade.  It's using a 3.6GHz Xeon E5-1650 v4.  I can set the number of points to 10 without any problems.  5 points will cause it to go non-responsive.  I would have no reason to run it with even 10 samples but again, the software isn't going to stop you from trying.

What is your current PC?
What is the smallest number of data points you require?
What application is requiring the lower number of points?

John Galbreath 2021/09/25 11:11

Same vintage as yours - tomorrow I will have time to try it again with faster processor.

My Beatty Standard is 100 mm in total length with a 75 mm mis-match (25 ohms) in center, requiring 2.5 GHz sweep of 8 points - 312.5 MHz step size yielding range of 100 mm and resolution of 0.21 mm.  This would square up the corners of my time-domain plot.

I should not expect so much from system costing so little.

Joe Smith 2021/09/25 12:00

That's a lot of error.

Why are you attempting to measure a metrology grade standard on a low end VNA with such a limited upper end?  Fun?

Joe Smith 2021/09/25 12:38

>From the paper you linked and I assume read:

Figure 23 shows the effect of both a narrow span and a wide span on the response resolution of a cable with connectors on each end and a termination. The response with the narrow frequency span is shown overlaid upon the response measured with a relatively wide frequency span. The wider frequency span enables the analyzer to resolve the two connectors into separate, distinct responses. The relationship between the frequency span and the pulse width in time is inversely proportional; the wider the frequency span, the narrower the impulse width and the faster the rise time.

Shown with V2Plus4 and 70mm airline Beatty, uncalibrated selecting a 2GHz and 4.4GHz upper end.

Joe Smith 2021/09/25 13:25

Attached showing the same home made Beatty on my vintage Agilent PNA with the upper frequency set to 1.5,3 and 4GHz.  Again, no calibration was performed.

John Galbreath 2021/09/25 17:15

On Sat, Sep 25, 2021 at 12:38 PM, Joe Smith wrote:

>
> From the paper you linked and I assume read:
>
> Figure 23 shows the effect of both a narrow span and a wide span on the
> response resolution of a cable with connectors on each end and a
> termination.
>

My Beatty standard was not terminated.

As I previously said:  " Expecting too much for system costing so little.  .  .  ."

Thanks for sharing your experiences.

Joe Smith 2021/09/25 18:25

On Sun, Sep 26, 2021 at 08:15 AM, John Galbreath wrote:

>
> My Beatty standard was not terminated.
>
> As I previously said:  " Expecting too much for system costing so little. 
> .  .  ."
>
> Thanks for sharing your experiences.

Terminating it will not have any effect on the measured length.   Maybe ditch that metrology grade Beatty you have and go back to your sections of long coax so you can have a better look at it.    You should be able to set your points to 50, 100, max and see what effects it has when keeping the range at 1M to 3G.  No calibration. Just run it and compare the edges.    Then repeat the same test with the upper set to 1GHz.     Get some idea what is happening, then go back and read that paper you posted.   It may make more sense.

Joe Smith 2021/09/26 08:50

On Sun, Sep 26, 2021 at 08:15 AM, John Galbreath wrote:

>
> " Expecting too much for system costing so little.  .  .  ."

I am not sure what it was you were expecting.  Your using the SAA2N which appears to be limited to 3GHz.  I doubt you were expecting it to perform like an 18GHz VNA when looking at TDR resolutions but maybe that's where your confused.  There are no settings in my software that can magically make that happen.

I picked up the V2Plus and V2Plus4 with all the options including shipping for just over $200.  The V2Plus4 was $130.  If OWO's team releases the V3, at $500 with the specs they mention, I will pick one up to review it.

Maybe you should start out posting your requirements.   You may find people are willing to help guide you, saving you both time and money.

John Galbreath 2021/09/26 09:23

Ran the same TDR parameters on a desk-top Windows7-64 bit i7-920 PC and no hang-ups.  PC thermometer increased by 45 degrees (F).  Thanks for advice.

Joe Smith 2021/09/26 18:35

Good to hear.   If you decide to get something with higher BW, you may want to have a look at the old HP8720.  These were offered with up to a 40GHz option.

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