Roger, we will need a little more info to help you effectively.
Which OS and version are you using on your PC? Win10/11? Win7? Win8? some flavor of Linux?
But a couple of first notes:
1. Don't use an OTG cable (those are for the USB micro-B connectors). A normal USB-A to C data (not charging) cable is required. For USB-C, OTG is normally a software function, but if your cable somehow does force OTG, it is the wrong mode for nanoVNA.
2. Assuming you are using some version of Windows, open Device Manager. Then expand the line that says "Ports (COM & LPT)" so you can see the individual devices. Plug in the USB cable and turn on your nanoVNA. You should see a new COM device appear. Note its identifier (e.g. COM6, COM10). When you turn on/off the nanoVNA, this device should appear then disappear. When you see this happening, you know that your cable and nanoVNA are correctly communicating with the computer. Only after that should you try to connect with a software program, and you need to select in that software program the identifier of this COM port and tell it to connect.
I hope that is helpful.
Stan KC7XE
