Author Topic: Real-time circuit tweaking while watching a miniVNA?  (Read 432 times)

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Offline elroy

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Real-time circuit tweaking while watching a miniVNA?
« on: December 31, 2018, 09:37:41 pm »
I recently bought a miniVNA Pro that I'm using with the provided vna/J software. My main use is looking at SWR, impedance, etc on ham antennas, transmission lines and impedance matching devices.

One of the main things I'd like to do is to set it up to do real-time measurement at a single frequency as the circuit is changed. For example, watch how SWR changes as a variable capacitor in an LC tuning circuit attached to an antenna is turned. I'm running into two issues. First, the software seems to want a frequency range as opposed to a single test frequency. Second, when it's runs repeated scans there's a nontrivial delay (usually of a couple to a few seconds) as the scan is completed. So it's slow-going to tweak and watch how the result changes.

Is there a way to do what I'd like to do? Or is this maybe not the instrument to use for this?

 

Online DaJMasta

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Re: Real-time circuit tweaking while watching a miniVNA?
« Reply #1 on: December 31, 2018, 10:21:02 pm »
Not sure on the miniVNA in particular, but a zero span mode should give you no sweep - though even narrow sweeps can give you useful information about the performance surrounding the frequency of interest (watching the curve shape will actually help you tune a single frequency quicker, since you can see where the area of interest is even when not centered on that frequency).  The delay may be linked to data transfer or computation time from the nature of the architecture of the instrument, but maybe it's worth looking around for ways to optimize update speed or look for videos of the unit in use to compare to what other people are seeing for delay times.  It is normal to see some delay just because of the sweeping nature and any averaging in place, but a reasonably fast VNA can usually give you pretty snappy measurements.  Maybe try lowering the number of points per sweep or increasing the RBW to see if it gets fast enough for your taste.
 

Online tautech

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Re: Real-time circuit tweaking while watching a miniVNA?
« Reply #2 on: January 01, 2019, 12:11:52 am »
Normal.

To see the bigger picture you need some span for the sweep and depending your RBW/VBW setting the sweep can take a while to complete.
Have a study of the screenshots and text here:
https://www.eevblog.com/forum/rf-microwave/antenna-project-log/
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