Fw: Re: [Antennas] 450 Ohm Ladder Line

2002年12月16日 20:36:48 -0800

Interesting thread. The wetting agents and even tap water contains
impurities which makes it a much better conductor than rain water which is
distilled by nature. Not sure just how much difference it would make but
might be an interesting test.
Distilled water (snow) is a very good insulator. I have personally seen 7KV
power lines laying on about 5 inches of snow and not tripping any of the
protective devices or melting into the snow. There were several dead weeds
protruding up through the snow next to the wire that were pretty well
burned, but the lights were still on.
73 N7BHB Dan
Correct, but what I wanted to know ....is it better to have a mismatch
at the load and loose some power due to the high SWR on the ladder
line (should be low because it's ladder line), or is it less of a loss to
add a toroid matching network at the load.
In my previous note on dB loss I'm amazed at the difference a wet line
makes, regardless of webs removed. For the #3 modified ladder line
DRY, its about 0.7dB/100ft better than RG-8 foam coax. For the #3
modified ladder line WET, its about 2.3dB/100ft worse than RG-8
foam coax (assuming water on the coax outer jacket has no affect).
Now, both N7WS and I used a "wetting agent" (I used a couple drops
dish detergent in the water) to allow complete coverage on the surface
of the polyethylene. The losses drop substantially if the water coverage
is not complete or it pulls into droplets. Using a wetting agent is
probably more representative of weathered window ladder line which
has less of a tendency to "bead". That also points out the benefits of
waxing the line .....but I don't know what the negative electrical
affects
of the wax would be.
Just as a sanity check, N7WS measured a drop of 5.5dB/100ft WET
at 50Mhz for the 551 line and I measured a drop of 7.6dB/100ft WET
at 50Mhz for the 551 line. That's a reasonable correlation since the
amount of water on the surface greatly varies the results. I ought to
go run the test again by sloping water on the line WITHOUT the
"wetting agent". When you wipe the line, still leaving some wet small
wet areas, it immediately returns to the DRY readings (or as best I can
see on the scope ...within -0.2dB.
73 Kees K5BCQ