[TowerTalk] hardline sweep - strange result

[John Keating]

I have two roughly 50m lengths of unterminated hardline that I swept in 
TDR mode using a RigExpert AA-600. Each has an N-connector on one end. 
The first length is Commscope CR-540PE (smoothwall 1/2" heliax) and it 
shows a good result with no discontinuities in impulse response or step 
response until the end of the cable, with the step response reflection 
coefficient at zero the entire run. The other length is Andrew FJS4-50B 
(corrugated 1/2" heliax). The impulse response is ok but the step 
response reflection coefficient drifts negative over the length of the 
run, ending at about -0.5 at the terminal end.

Why does the FSJ4 show that result? Note that when terminating that run 
into 50 ohms, the step response reflection coefficient is zero across 
the run.

John K7LY