How to measure velocity factor of coax using NanoVNA

I had posted about measuring length of coax using NanoVNA with the transform function. In that method, we use the velocity factor of the coax in percentage. If we give the velocity factor as 100% instead, we get the electrical length of the coax. The ratio of the actual length to the electrical length measured in NanoVNA should be the velocity factor. Velocity factor is the ratio of the speed of radio wave in the concerned medium to that in vacuum. It is inversely related to the square root of the dielectric constant of the coax insulator. When I measured with velocity factor set as 100%, I got a value of 13.18m for the electrical length of the cable. Calculation using the physical length of the cable as 10m, I got a velocity factor of 75.87%.

In the initial measurement, I had used an SMA jumper wire. I removed that wire and connected the cable once again. This time I got 12.88m as the electrical length of the cable. With that value, the velocity factor was 77.63%. What I have not taken into account are the PL259 connectors at both ends of the cable and SO239-SMA adapter for attaching to the NanoVNA. The listed value of velocity factor which I have seen online for HLF 200 cable is 83%. There is another method of measuring velocity factor in NanoVNA using both ports together. But I do not have an additional SO239-SMA adapter needed for connecting the coax to the second port. Here is a recap of my earlier post on how to How to measure length of coax with NanoVNA.