On Sat, Jul 18, 2020 at 6:47 PM Tim Reimers KA4LFP <treimers95@...> wrote:
I have a nano VNA that is now refusing to read correctly after calibration it seems.
After running a one port calibration using the calibration assistant,
using the supplied open, short, and load calibration elements
... My normal technique is to do a scan of the Load element at the frequencies I have selected (before the calibration)... expecting to see a
dot n the middle of the Smith chart and a straight 1:1 line on the SWR chart, as I believe the load element should be 50 ¦¸ of pure resistance.
But as of yesterday that is not now how the device responds.
The Smith chart is covered in zigzags instead of even trying to be circles, and the SWR chart looks like a seismograph measuring a 5 on the Richter scale!
Well, several things come to mind. First, did anything of note happen "yesterday" ? It is pretty easy to burn out the port if you accidentally transmit into it, or connect an "active" antenna which feeds back power into the VNA. Simpler question is are you using the correct port? The Nano VNA is not a two port device, it transmits only on one port (I don't really expect this to be the case but in the interest of completeness ...) Do you have a different load? If not do you have a 50 ohm resistor you can solder across a cable and plug that in and see what you see?
Things that might be helpful when using your VNA, a 6 dB pad to mitigate the effects of high SWR, and/or a DC blocker.
If you do the through port calibration does that work as expected?
--Chuck
AI6ZR
Chuck