Ladder Line Page 2

Copyright © 2002 - 2015 by Harold Melton, KV5R. All Rights Reserved.

Ladder-Line Types

No one seems to know what to call it: ladder-line, windowed ladder-line, window line, “true” ladder-line, open ladder-line, open feeders, etc. etc.

  • Twin-lead is the 300-ohm TV antenna line. Don’t mess with it. A similar line is called tubular, the type of TV line that is oval and contains a foam dielectric. It's almost as lossy at high SWR as coax.
  • Ladder-line uses mostly air as the dielectric. The wires are separated with spreaders or window-punched plastic.
  • Windowed ladder-line (WLL) is just that: 1-inch twin-lead with windows punched in it. Some call it window-line.
  • The “true” ladder-line is best called “open-wire feed-line,” to distinguish it from window line. This is the type made from two parallel wires, separated by spreaders.
What to Get

Get the 14-gage stranded window line from Cable-Xperts or Wireman. Don’t get that 18-gauge solid-wire stuff—it breaks when repeatedly flexed. Well—some people swear it lasts forever. I guess it will if you completely immobilize your connections.

Brew Your Own

The one problem with window line is that it tends to change characteristics when wet, and the longer the run, the more tinkering you’ll have to do with your tuner as the weather changes. The solution for long runs is to make your own open-wire feeders. It isn’t hard or complicated.

  1. Get a 500-foot roll of #14 THHN or THWN insulated stranded ($20 ~$45 at builder’s supply). Pick a color that blends with the background. Get some pressure-treated 2x4s, 10-12 feet long, and plant them in the ground every 50 feet or so. Many people do not use any poles; they just swag it from the tower to the eve of the house, and it works fine. Poles would be needed for runs over, say, 150 feet or so. It depends on what wire you use.
  2. For spreaders, all you need is some kind of small, UV-resistant, semi-rigid plastic pipe, like 3/8" PEX. Cut them 4-5 inches long, and make enough to put one every 5 feet or so. Use your table saw or table router to cut a little notch in each end of each spreader, what ever size is needed to snugly fit your wire. You can also drill holes in each end, slide a bunch of them on the wires, then space them out, then glue them in place. You can also purchase pre-made snap-on wire spreaders.
  3. String up two strands of the wire, appropriate length, between trees. Pull them even. Insert a spreader every few feet. Inject a dab of hot-melt glue in each end of each one to secure them to the wires.
  4. Congratulations - you just made modern, high-quality “true” open-wire ladder-line, and you didn’t even have to boil a bunch of wood dowels in paraffin!
  5. Now attach it to your supports with little electric fence insulators (on wood posts) or PVC pipe stand-offs (up the tower), as needed.

Note: Purists think you have to use “bare” wire - baloney. Why mess with wind static, rain static, and corrosion? The same holds true for all wire antennas. Never use uninsulated wire. It just isn’t necessary. Of course, if you already have a bunch of it, feel free, and maybe spray paint it…

One more thing to consider: Bending ladder-line at sharp angles can cause problems on the higher bands. This is because the magnetic field around the line will interfere with itself at the bend. Or so say the books! I have never had any problems bending window line at 90-degree angles, and I’ve even fed a 2-meter beam with window line, bent 90 degrees 3 times, and it worked great!

Continued…

12 thoughts on “Ladder Line Page 2
  1. I was looking at the low loss’s and thought it might do well for my RC Airplane antennas at about 50ft lengths. I read somewhere that 450 ohm ladder line would work well about 2 mtrs because the gap needs to be less than 1% of the wave length and at 1.2 Ghz that would be about a tenth of an inch or 2.5mm. Would common 2 conductor wire, like lamp wire work or is there some other issues with the balanced line at higher frequencies?

      • Years ago the ARRL labs did a test of 18-gauge lamp cord at HF and found the line impedance to be, if I remember, about 110 ohms, and it was quite lossy, due to dielectric heating of the continuous and relatively thick insulation. If it’s quite lossy at HF it will be terrible at UHF!
        As far as I know (which isn’t very far!) parallel lines are used for UHF and microwave only on printed circuit boards; and modules are interconnected with very short teflon RG-174 or similar.
        Another example is wi-fi hotspots — they run Ethernet with PoE and put the transmitter atop the pole, connected directly to the antenna, as any feed-line is too lossy.

  2. I have an 80 meter Loop fed with 30 feet of coax twin lead made from rg58 coax,will I gain anything by replacing it with homebrew ladderline?

    • I don’t know. I’ve read that twin coax feed-line is very low-loss at high swr, and at only 30′ run I don’t think you’d see much if any difference. But I’ve never seen any actual comparisons. If you do switch to LL, please take some before & after measurements and post them back! You could pop some 4″ spreaders between your coaxes and feed the shields.
      73, –kv5r

  3. I have about 140 feet of doublet antenna (70 feet each side of center) and this comes into about 42 feet of home made ladder line, a 4:1 balun, and into the Kenwood TS850 auto tuner on a one foot co-ax.

    With that setup, the lowest I could go was 7.183, and 3.974. I added more and more ladder line, and I can now tune almost to the bottom of 80 meters, plus quite a bit of 160 meters, and all the others. Now I have it draped all around the shrubbery.

    My question is… I don’t have room for all the extra ladder line, it was just a tuning experiment, BUT will cutting some of the original length off get me into tuning range again, or will I just lose all the low bands?

    • Well, I’m sure you know, radio’s internal auto-tuners have a pretty narrow range.

      Whether cutting your L-L shorter will bring it in range, at all desired frequencies, or not, is a seriously complex NMC problem, so you have to just try it and see. First remove the 4:1 balun and see what happens.

      I don’t think you’ll get there with an internal radio autotuner. Those are typically meant to handle a 3:1 swr, the better external tuners handle 10:1 or more. Think of the impedance at the radio end varying in a sine wave as a function of the length of the L-L, at some given freq, then think of that being in-range of an internal autoutner at all HF bands! It’s complex.

  4. I wanted to say thank you for posting this! I have wanted to play with ladder line for a while, but when I mentioned it I heard so much misinformation. Following your article, and adopting a “screw it, we’ll just see what happens” approach. I am now running an inverted-v dipole operating from 80-10m with no problems whatsoever fed with 450 ohm window line. I absolutely love it! I have even had quite a bit of success running at outputs as low as 1 watt on 40 and 80 and getting 1,000 mile plus QSLs, and the band conditions are not great right now. Can’t wait for the peak of the next solar cycle!

    Thank you again! K4RJD – Richard D.

    • Glad you liked the article.
      Yeah, most hams just can’t believe how lossy coax is until they switch to ladder-line. But they sure do like to get on the air and spread misinformation and opinions. I’ve heard it all.
      73

  5. This is fantastic. Sometimes I see the same basic info. paraphrased endlessly but I logically form questions which someone like you comes along and answers with working examples which exceed the status quo. Thank you. I will now make the open wire feed I’ve been hesitating to do. It’s, even, mainly for a valve Halicrafters receiver meant for direct hookup this way. I’ve been doing the random wire with L-match, but would like to try a zeppelin or something (something I can transmit on, also, with up to 100 watts after I get my General ticket). I have the wire to make the feed line and elements, the extra air cap to turn the L-match to a T or Pi or something, and you just dissolved my inhibitions. Thanks! W4VEY Jeff Burris, FL

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