New user of NanoVNA H4. Bought it to tune some 500 MHz stub traps but sure I will find many other uses. Tried TDR function on a spool of coax and got factor of 2 difference on needed max frequency for the length (needed to lower frequency). Then I found another example that looked to double that (4 times what I ended up with). May just be some setting changes but would like to understand the differences or if I have just made some error.
The example I was following is https://www.youtube.com/watch?v=9thbTC8-JtA
They gave the approx. max freq as: Freq (MHz) = 5850 x vel factor/length in meters
which for 250 ft (76m) and vel factor of 0.70 gives about 54 MHz
I ended up at 31 MHz to just get the reflection pulse on the right side of the screen. The video has been up for a while and I found no corrections so I am guessing some setting is different but I believe I followed all the settings given. Any insights on this would be appreciated.