[TowerTalk] Coax Losses on 160 and 75?

[Steve Hunt]

Some of the accuracy issues can be explored using Dan's excellent TLD 
software. Say we had 150ft of Belden 9201 which we were trying to 
characterise for loss on 160m; TLD predicts a matched loss of 
0.449dB/100ft at 1.9MHz.

A 2-port analyser S21 measurement - assuming the analyser provides a 
perfect 50 Ohm termination - would predict 0.446dB/100ft loss. The error 
is because the analyser port would need to be 53.4-j1.4 to provide a 
matched termination for the line.

An S11 measurement with the line short-circuited at 2.11MHz - the 
nearest frequency where the line is an even multiple of a quarter-wave - 
using the approximation that Zo is 50 Ohms, and using the simplification 
that loss(dB)=8.96.Rin/Zo, predicts a loss of 0.519dB/100ft _at that 
frequency_.

Those discrepancies to not include errors due to the inaccuracy of the 
analyser.

Steve G3TXQ