Ladder Line

Copyright © 2002, 2006 by Harold Melton, KV5R. All Rights Reserved.

Amateur Radio Ladder-Line: The Myths

Ladder-Line 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:

  1. “Ladder-line radiates!” Baloney. ladder-line does not radiate any more than does coax, if terminated in a balanced antenna.
  2. “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.
  3. “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.
  4. “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.
  5. “I can’t buy a lightening arrestor for ladder-line!” So just make them yourself, as shown below.
  6. “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.

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8 thoughts on “Ladder Line
  1. Ok new guy here …g5rv using a alum military pole on my rv im portable they are saying not to have ladder line up aginst the metal pole but what if said pole is isolated from ground..? Im in the oilfields of southern texas fulltime rver so trying to be more portable than most….jimbo

    • It’s doesn’t matter if the pole is grounded or not. If the ladder line is too close to it, the line’s magnetic field will induce RF into the pole, thus turning some of your power onto heat. You can make stand-offs pretty easily with 1/2-inch PVC. Make them ~6 inches long; drill a hole thru each end; secure the pvc standoffs to the pole with cable ties (or wire); and secure the ladder line to them with cable ties (or monofilament fishing line).

      Hey where in Southern Texas? I grew up in the RGV, near Harlingen.
      73,
      –kv5r

  2. Ladder line at 14 or 16 gauge is a bit pricey when running 100 ft. How about using some spacers and tie wrap to make true (not windowed) ladder line?

    • Sure, true ladder line is best, if you don’t mind the work of making it. It will perform a little better than windowed line, particularly when wet, and have lower wind-loading. I’d use #14 insulated stranded THHN wire (or #10 for high-power), and perhaps some 1/4-inch thin-wall UV-stabilized acrylic tubing for the spacers (3-4 inches), notched on each end using a suitable jig on a router table (or similar); pull two wires taut between trees, insert notched spacers every 3-4 feet, and glue ends with silicone caulk or hot-melt.
      Of course, any copper wire it way too expensive nowadays. I once made ladder line from #17 aluminum (electric fence) wire, and pieces of plastic clothes-hangers for spacers, and it worked OK for a 50-foot or so run.
      73,
      –kv5r

  3. On a G5RV how close can I come to a 4ft chainlink fence with the latter line? Also can part of the latter line touch the ground? I plan on burying the coax run thru the back yard to the house.

  4. Was wondering about the interaction between the ladder line from a G5RV feedpoint to a balun and a 5mm wall aluminum pole that is supporting the G5RV feedpoint. Since I was going to rig up a pulley on the feedpoint pole to lower and raise it in need, what should I do about keeping ladder line away from supporting pole?

    73 de ZR1HPC
    Hylton

    • Hi,
      You need to keep the ladder line away from the pole, at least 2x-3x width of the line. You could bring the line away from feedpoint at an angle, or mount your pulley on an angle-bracket to offset the feedpoint about 15-20cm from pole then bring ladder line down parallel to pole. Either way you need to mount the balun to a stand-off bracket of some kind. Be sure to put a few twists in the ladder line so it won’t flop in the wind like a ribbon.
      73, –kv5r

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