Hi Joel,
Nice to hear from you!
The ladderline loss figures quoted in the Antenna Book - which I believe
are also repeated in TLW - are out by a factor 2. It's very easy to
demonstrate that with a simple I^2R loss calculation. I'm happy to show
the sums if you need convincing.
Tenths of a dB differences may not matter of themselves. However, they
*do* matter when the losses you are trying to measure are of the same
order. In your article you said that the measurements on dry line agreed
with TLW predictions "within a few tenths of a dB in each case". Given
that the TLW loss figure for ladderline is 0.05dB at 3.7Mhz, measuring
something "within a few tenths of a dB" of that figure could represent a
*gross* difference.
Also, we need to remember that in many (if not most) Ham applications
ladderline is operating at a high VSWR, so what might seem to be
negligible differences in *matched* loss figures become much more
significant in real life applications.
I think the most puzzling result you reported was the substantial
increase in loss (3dB to 10dB) when you set the line on dry ground,
whereas there was virtually no increase in loss when you set the line on
wet ground. When (or is it if) our UK weather improves, I intend to try
some measurements myself.
73,
Steve G3TXQ
On 27/01/2012 02:44, Joel Hallas wrote:
Steve,
Well, I'm not sure if TLW is exactly on or not, but I'm pretty comfortable
with our technique. When we're talking differences of 0.1 dB, not sure if
the exact value is too critical for the usual HF amateur.
Bob and I took careful data, rematched with every new set of data to
compensate for any Zo differences and used good, commercially calibrated
gear to take the data.
Regards, Joel Hallas, W1ZR, BSEE, MSEE
Westport, CT
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