On Sat, 23 Sep 2006 00:27:39 -0700, Roy Lewallen
wrote:

In an experiment I did many years ago with 300 ohm twinlead
(http://www.eznec.com/Amateur/Article...eed_Lines.pdf), I found
that the loss of wet line was significantly different just after it
rained (when the line had presumably accumulated dust) than after it
rained for some time.

Hi Roy,

Some time before Wes's article was published I tried to measure the
stuff myself. I used an eighty foot length of the so call "450-ohm"
window line. My problem was that I really didn't have very good
equipment for making the measurements. I use both a MHJ-259B and an
Autek RF-1. I took several measurements and plotted the results
getting a relatively good scattering patterns and went with that. The
line I used was brand new and clean. For wetting I sprayed the line
using a fog nozzle which makes a good fine mist that "stuck" well.
(Being a damp area I don't have the drying problems Wes has in Tucson)
As best as I could determine the wet losses were about double those
for the dry line. But, as I said my equipment was ham-grade at best so
I sure wouldn't bet the farm on my findings. (Interestingly, I did
measure the dry line's impedance at 408-ohms which matched Wes's
findings right to the ohm.)

AsI mentioned earlier post, I tried using window line here on the
northern coast and found that after being up for about a year I had
moss starting to grow on the line. Now that certainly is going to
crank up the losses!

The bottom line is I gave up using the stuff and, for my tuned fed
applications I use open line.

Danny, K6MHE

Danny Richardson wrote:
As best as I could determine the wet losses were about double those
for the dry line.

Wow, from 0.2 dB to 0.4 dB. :-) Would the following
work for measuring the wet/dry losses of 1/2 wavelength
of ladder-line shorted at one end and an MFJ-259B on the
other end? Measure the resonant purely resistive impedance
at the open end. Wet the ladder-line and repeat the
procedure. Calculate the losses.

If the line were lossless, zero ohms would be read.
The deviation away from zero ohms yields the magnitude
of the loss in the line at the 1/2 wavelength resonant
frequency. That's about 8.8 MHz for 50 ft. of ladder-line.
--
73, Cecil http://www.w5dxp.com

On Sat, 23 Sep 2006 14:32:19 GMT, Cecil Moore
wrote:


Wow, from 0.2 dB to 0.4 dB. :-) Would the following
work for measuring the wet/dry losses of 1/2 wavelength
of ladder-line shorted at one end and an MFJ-259B on the
other end? Measure the resonant purely resistive impedance
at the open end. Wet the ladder-line and repeat the
procedure. Calculate the losses.

If the line were lossless, zero ohms would be read.
The deviation away from zero ohms yields the magnitude
of the loss in the line at the 1/2 wavelength resonant
frequency. That's about 8.8 MHz for 50 ft. of ladder-line.

You are assuming something that I am not. That is the measurements
were accurate. Measuring anything to a fraction of a dB is most
difficult - even with the best of equipment and mine was not.

Danny, K6MHE