Copyright © 2002, 2006 by Harold Melton, KV5R. All Rights Reserved.
Amateur Radio Ladder-Line: The Myths
ladder-line is great - extremely low loss, even at high SWR. However, many hams refuse to use it because they are afflicted by common misconceptions:
- “Ladder-line radiates!” Baloney. ladder-line does not radiate any more than does coax, if terminated in a balanced antenna.
- “I tried it once, and it messed up my TV, my computer, and filled the shack with RF!” The trick here is simply to make sure you use a length of ladder-line that is not a multiple of a half-wavelength on any band. Lengths like 43 and 86 feet work well. A resonant length of ladder-line, just like the shield of coax, will pick up RF from the antenna and conduct it into the shack. The only difference is that the shield of the coax is grounded, and the ladder-line is not, so it acts in common-mode to bring in and radiate induced RF. A non-resonant length of feed-line will present a high impedance to common-mode currents. And, as with any feed-line, it’s best to run it perpendicular to the antenna as far as you can so the EMF from the dipole will cancel itself instead of inducing current in the feed-line.
- “It’s too hard to work with! You have to keep it away from metal!” Well, yes, a couple inches or so. The general rule is twice the width of the line. It’s easy to make stand-offs from half-inch PVC pipe. Ladder-line can cross a metal edge, like a window sill; you just don’t want to run it right against metal for any significant length.
- “It’s too hard to bring into the shack!” Baloney. There are many waterproof ways to bring ladder-line into any shack. One is shown below.
- “I can’t buy a lightening arrestor for ladder-line!” So just make them yourself, as shown below.
- “It flops around in the wind, and it breaks too easy!” (a) Windowed line should be twisted about one twist for every two feet to prevent wind-induced oscillations. (b) Make a good feedpoint connection, with proper strain-relief. It doesn’t hurt to wrap it over the top of your feedpoint insulator and then secure it to itself with cable ties. Also, the 14-gage stranded stuff is much more reliable than the old, cheap 18-gage solid stuff.
If you run an all-band dipole (with a tuner in the shack), you need ladder-line. Coax is very lossy when operated at high SWR. It’s easy to lose 90% of your power in your coax when operating on bands where the non-resonant dipole presents a high feedpoint impedance to the feedline.