I wrote about some of this in this forum back on 4/13.
BTW, my paper was never in QST but it was in Vol 6 of the ARRL Antenna
Compendium, p. 174. A draft copy is here: http://k6mhe.com/n7ws/Ladder_Line.pdf
Wes N7WS
On 4/21/2019 2:36 PM, Jim Brown wrote:
Hi Mike,
I see several possible issues. Like Jim Lux, I don't trust the loss data nor
the measurement technique. Far better would be swept S11 measurements of a
known length with the far end open and shorted, and post-processing in AC6LA's
ZPlots. From my own experience attempting to measure paired lines, the most
critical part is dealing with the interface between an unbalanced analyzer and
the line. KN5L does this with a carefully wound transformer at the output of
the analyzer, with calibration performed on the output side of the transformer
(that is, where the line is connected).
The other possible issue is absorption of rain by the foam, and it's effect on
characteristics of the line. Many years ago, QST published excellent work by
N7WS on the greatly increased loss of window line when it is wet. That piece
is reprinted in one of the ARRL Antenna Compendiums.
73, Jim K9YC
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