Bob,
Perhaps I had better explain clearly why I am carrying out these
ladderline tests.
I believe that the "wet" ladderline losses reported by Wes Stewart, and
those predicted by at least two of the popular on-line calculators, are
sufficiently high that some folk could be put off using the stuff. It
seemed to me important to understand: how Stewart arrived at his
figures; why Stewart's figures are so different from the ARRL
measurements; what sort of losses can be expected in practice.
That's all :)
73,
Steve G3TXQ
On 03/08/2013 14:37, Bob McGraw - K4TAX wrote:
Steve et al:
I'm not saying that loss does or does not change with the vinyl type
window line between wet and dry. I do agree with your results in that
loss does increase with a wet line as opposed to a dry line. I also
agree that loss is greater per unit at 28 MHz vs. the same length of
line at 1.8 MHz or 3.8 MHz regardless if the line is wet or dry.
My point, with today's receivers, in most all cases the atmospheric
noise and man made noise will mask any receiver internal noise and
will easily overtake any loss in the transmission line. However, the
loss in the transmission line will affect the NF of the receiver,
which on HF is of little significance. In many cases, we worry about
2 or 3 dB loss in the transmission line but run the attenuator of 10
dB to 20 dB at the input of the receiver. Now on transmit, that point
makes a different in the power arriving at the antenna. Again,
typically less than 1 S unit on the other end. To that point, most of
the time I run the Argonaut VI at 10 watts and can work about any
station I hear, regardless of line loss.
True open wire line, by definition, is two conductors supported only
at the source end and the termination end, drawn taught, and without
any spacers. This of course is a real challenge to make work reliably
in practice unless one uses large conductors and spaced at 6" to 18"
and used at lower frequencies and typically with very high power in
the near megawatt range. We used this feed line approach in some of
the commercial SW stations to which I attended. Some of these feed
lines were each several thousand feet in length. All of this is far
beyond the scope of most ham installations.
I would like to see more data on dry line vs. wet line from natural
cause as opposed to "wetted" line. I use the vinyl covered line with
66% of the web spacers removed. {Remove 2, leave 1, remove 2, leave
1.} I see little change from wet to dry on HF.
73
Bob, K4TAX
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