[TowerTalk] Measuring Coax Length

[Jim Brown]

On 10/28/2014 2:39 PM, Jim Lux wrote:
> For TDR (or looking for integer half wavelengths as you sweep the 
> frequency on an analyzer) you have to assume a particular propagation 
> factor,

Mike,

Measuring the length of a long piece of transmission line is tricky for 
several reasons, most important because Vf (the velocity factor) varies 
a bit with frequency.  Study k9yc.com/Coax-Stubs.pdf

An easy way to get close to the actual length is to put a connector on 
one end, leave the other end open, and measure the impedance with an 
antenna analyzer. At every frequency where it's some odd multiple of 
quarter waves long, it will look like a short. So sweep it with whatever 
analyzer you own, write down those frequencies, and do the arithmetic.

73, Jim K9YC