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
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