On Sat, 23 Sep 2006 02:48:16 GMT, Cecil Moore
wrote:

Danny Richardson wrote:
Just drop by my qth anytime between November and May.

How do you keep the water on the feedline? Mine
always beads up and falls to the ground.

I don't do anything. Ever heard of Oregon mist?

When I first moved up here on the northern California coast I put up a
doublet feeding it with window line. The next spring when I dropped
the antenna for some maintenance I found moss growing on the feed
line.Need I say it was replaced with something better?

Danny

You probably should read the article yourself, but Table 1 of the article
contains columns for matched line db attenuation per 100 feet for dry and
wet lines. This set of data is from measurements made at 50 MHz. Since
attenuation scales as the square root of frequency, I came up with a rough
estimate for loss at 7 MHz. The author then goes on and uses modeling to
predict some surprisingly large line losses for the G5RV antenna at 1.9 MHz.

"Owen Duffy" wrote in message
news
On Sat, 23 Sep 2006 00:48:43 GMT, "John, N9JG"
wrote:

An excellent article. It appears to indicate that at 7 MHz a feed line
made
from 100' of Wireman 554 window line would have a loss of about 2 db when
the line is wet. When the line is dry, the loss is insignificant.

Is that the matched line loss you are talking about.

These lines aren't always or even often operated at very low VSWR, so
it may be unwise to dismiss the loss as insignificant in the general
sense.

Owen
--

The author used a wetting agent.

"Cecil Moore" wrote in message
m...
John, N9JG wrote:
An excellent article. It appears to indicate that at 7 MHz a feed line
made from 100' of Wireman 554 window line would have a loss of about 2 db
when the line is wet. When the line is dry, the loss is insignificant.

I've often wondered how someone "wets" a vertical feedline
without using soap.
--
73, Cecil http://www.w5dxp.com

On Sat, 23 Sep 2006 04:32:51 GMT, "John, N9JG"
wrote:

You probably should read the article yourself, but Table 1 of the article
contains columns for matched line db attenuation per 100 feet for dry and
wet lines. This set of data is from measurements made at 50 MHz. Since
attenuation scales as the square root of frequency, I came up with a rough

A widely accepted line loss model is that attenuation = k1 * f^0.5 +
k2 * f, your approximation makes k2=0.

estimate for loss at 7 MHz. The author then goes on and uses modeling to
predict some surprisingly large line losses for the G5RV antenna at 1.9 MHz.

Not surprised at all, many of the figures in the article at
http://www.vk1od.net/G5RV/index.htm show the loss in ladder line in a
G5RV feed system. Fig 3 shows that dry ladder line loss is not
insignificant in the general sense, and Fig 8 shows the expected
degradation on "wet line" in that application using Wes'
characterisation.

Owen
--

John, N9JG wrote:
You probably should read the article yourself, but Table 1 of the article
contains columns for matched line db attenuation per 100 feet for dry and
wet lines. This set of data is from measurements made at 50 MHz. Since
attenuation scales as the square root of frequency, I came up with a rough
estimate for loss at 7 MHz. The author then goes on and uses modeling to
predict some surprisingly large line losses for the G5RV antenna at 1.9 MHz.

Resistive conductor loss is proportional to the square root of
frequency, because of the relationship between skin depth and frequency.
The loss of wet ladder line is almost entirely dielectric loss, not
resistive conductor loss. In good dielectrics, loss is directly
proportional to frequency. However, water is quite different from a good
dielectric and with different loss mechanisms, so I wouldn't hazard a
guess as to how it might vary with frequency.

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.

Roy Lewallen, W7EL

Owen Duffy wrote:

A widely accepted line loss model is that attenuation = k1 * f^0.5 +
k2 * f, your approximation makes k2=0.
. . .

In that model, k1 is attenuation due to conductor resistance, which is
proportional to the square root of frequency as long as the conductor
thickness is at least several skin depths. K2 is dielectric loss, which
is proportional to frequency for good dielectrics. So this model is good
for common transmission lines like coax or dry twinlead, at HF and
above, but not necessarily valid for loss due to water. I commented more
about this in another posting.

Roy Lewallen, W7EL

On Sat, 23 Sep 2006 00:32:04 -0700, Roy Lewallen
wrote:

Owen Duffy wrote:

A widely accepted line loss model is that attenuation = k1 * f^0.5 +
k2 * f, your approximation makes k2=0.
. . .

In that model, k1 is attenuation due to conductor resistance, which is
proportional to the square root of frequency as long as the conductor
thickness is at least several skin depths. K2 is dielectric loss, which
is proportional to frequency for good dielectrics. So this model is good
for common transmission lines like coax or dry twinlead, at HF and
above, but not necessarily valid for loss due to water. I commented more
about this in another posting.

Roy, I agree re the wet lines application. A further issue is that of
standardisation of the wet line.

Wes' work and yours shows that there is a degradation, but there is
uncertainty regarding the scale of degradation, and effects like salt
build up in marine locations could be expected to influence results at
the start of rainfall and after torrential rainfall for instance.

I do often use TV ribbon for temporary / portable antennas, tuning the
antenna by adjusting the feedline length. I tend to avoid ground
dependent antennas for this purpose, and a dipole with TV ribbon has
some advantages, but as you note in your article, and as we have all
observed, the "tuning" changes with rainfall more than would be
observed with a coax feedline.

Since your article was published, RG6 has become popular for TV
feedline, and is cheap as chips. It performs very well, and I find
myself using it for portable antennas. RG6 is a little heavier than
RG58C/U (~30%), a little thicker, but has relatively low loss,
approaching that of RG213 as a dipole feedline.

I wonder if anyone has every critically appraised various forms of RG6
for through braid leakage and IMD? I know there is variability in
quality, some seem to not locate the centre conductor in the true
centre of the dielectric, and aluminium wire braid can be a
disadvantage for solder-ability. (Cecil will correct the spelling if
you don't know what I mean!)

Owen
--

Cecil Moore wrote:

Danny Richardson wrote:

Just drop by my qth anytime between November and May.


How do you keep the water on the feedline? Mine
always beads up and falls to the ground.

No it doesn't!! You just can't see what surface tension causes to 'stick'

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