Re: Using the AVNA with the nanoVNA-saver control program

Bob Larkin

Hi Mike,

What OS are you running? With Ubuntu I get stable operation, even if the serial port is not available. Or if it comes and goes!

What seems to work is to plug in the AVNA USB cord and then start the n-saver program. It always seems to see the serial port. That makes sense in that the Teensy when it is first started identifies itself over USB as a HID (human interface device). This is used for fast load of programs. Once the user program is taken out of flash and runs, the Teensy changes into a Serial Device. By starting the Teensy first, it is already a Serial Device when the n-saver goes looking for it.

Also, there is software in version 0.70 to use a dedicated serial UART (the Teensy has several). If the USB serial causes problems, we could explore using "HWSERIAL4". I am hoping we don't need to use that, but it is there. It needs some added hardware to convert 3.3 Volt logic to RS-232.

Also, the n-saver program will not show a serial device unless it is a listed VNA.

On the startup measurements, I am not sure. What you are seeing is normal. But, one issue is that the audio measurements are slower than RF ones. This makes the 101 measurement block annoying at times. Rune has indicated he will pursue a programmable length block when he gets time. This would be nice.

And points outside the Smith Chart unity reflection coefficient circle correspond to negative resistances. These occur with active devices, but aren't supposed to with passive components. BTW, I'm so old that in my youth I knew Phil Smith, and did some work with him! He gave me a Smith Chart calculator, once, that I still have.

Lastly, I am going to look for an inductor that I wound on PVC pipe. Most anyone could duplicate it and it should be quite repeatable. Wecould compare measurements. It is in a box, somewhere!


On 2/12/20 1:13 PM, Mike Runyan via Groups.Io wrote:
Bob, thanks for the help.  What you said about the CALSAVE and 50ohm not affecting impedance measurements is good to know and now makes sense of the data I saw.  The spiral measurement is messed up is good to know.
I'm not an amateur radio guy but have an interest in RF stuff.  Still trying to get my head around smith charts.  The off the chart spiral didn't help me any.  That isn't possible, right?  I'm not sure what I did to stop it.  I put version .61  back in to verify the hardware was ok and it seemed to be.  Nice that the EEPROM data can be used from either version.  I re-installed .70 and it still did the spiral thing.  Think what made it finally go away was to do the CALSAVE 0 & 1 over, but I'm not sure.
nanoVNA-saver has crashed many times, usually serial port related.
Why does the measurement happen twice.  It does the sweep, then about 25 seconds later plots it and then it does another sweep that it doesn't  plot?
Is the ~25 seconds after the sweep all nanoVNA-saver calculating?  Could it display a count down or something?  Should I be asking the nanoVNA-saver author this kind of stuff or posting here?

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