On Fri, Jun 9, 2023 at 01:26 PM, Jim Lux wrote:
It's useful to know how to make the TDR work - I've found more than one
feedline problem by using TDR - yeah, sometimes if there's combinations
of solid, foam, and air dielectric, the distances don't work out, but
you can still see the discontinuities from connectors.
The TDR feature in NanoVNA Saver has some issues. In 5.5 it does not plot the time graph correctly. In all versions the impedance graph was not correct in the initial release and still has problems. I find doing TDR on the NanoVNA itself is easier and the NanoVNA app TDR display plots impedance much better. Take a look at the attached plots from a NanoVNA-H4 , NanoVNA App and Saver. The first scan is 25 feet (7.62 meters) of RG58 and the second is with 8 feet (2.4 meters) of RG6 added on the end. Nominal impedance of the RG58 is 50 ohms and the RG6 is 75. Note how NanoVNA App resolves the impedance of the two transmission lines
Roger
Roger Need
