Results of the Bexar Operators Group “Ladder Line” Testing
It was a great day for doing a few tests involving 450 Ohm “ladder line” as several members of the Bexar Operators Group met at the John James Park to compare the findings of the recent ARRL tests on this lead-in vs real life testing.
If you read the ARRL article in the November issue of QST, you’d note that the readings and findings they did were “static tests” using measuring equipment and NOT actual operating tests. For our testing we did the same “static tests” they did with basically the same results. After this initial testing, we then did what they failed to do: We used this setup but applied varying amounts of RF power through the water – saturated (near ground level) ladder line while observing the swr readings.
At 5 watts CW key-down, the results were the same. At 10 watts key-down, the swr started to change. By the time we reached 100 watts key-down the swr went “crazy” varying from 1.2:1 to infinity:1 ! When we attempted to send an SSB signal at 100 watts, the swr readings had even bigger “fits” and I swear the line almost started to squirm like a snake.
It’s a good thing we were using safety procedures or we probably would have blown our transmitter! I knew this would happen because it happened to me about 25 years ago when I used a G5RV antenna on the top of an elementary school and when the ladder line got saturated, and at one point there was a small pool of water it laid in, I had the same crazy swr readings.
Lifting the line at least 6 inches above any “pooling” solved this problem.
My recommendations: If you use 450 ohm ladder line, keep it away from conducting surfaces with standoffs, keep it away from any area where water might pool up, twist the lead every two feet or so, and when you install it coat the line with a thick layer of car wax as this helps keeping it from coupling to other surfaces when it gets wet. If you use this line as a feed, try to keep it more vertical than horizontal.
(The Bexar Operators Group is an investigative amateur radio group and not a social radio club. All are invited to attend our experiments and operations. We also do EmComm work and development.)
Bob W2IK / W5BOG
