Ladder Line

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

Why Use Ladder-Line?

To efficiently feed a non-resonant multi-band antenna.

Antenna Mythology

Resonance

First, let's dispel the greatest myth in antenna theory: Antennas must be “resonant” to be efficient. Baloney! It just ain’t so!

Please recognize that an antenna need not be resonant in order to be an effective radiator. There is in fact nothing magic about having a resonant antenna, provided of course that you can devise some efficient means to feed the antenna. Many amateurs use non-resonant (even random-length) antennas fed with open-wire transmission lines and antenna tuners. They radiate signals just as well as those using coaxial cable and resonant antennas, and as a bonus they usually can use these antenna systems on multiple frequency bands.

ARRL Antenna Book, Ch. 2

As long as the length of the antenna is at least a half-wavelength at its lowest intended frequency, its efficiency is well over 90%, just like a resonant dipole. The problem is getting power to it—coax is very lossy (due to dielectric heating) unless terminated into its characteristic impedance, and this effect is what leads most hams to erroneously believe that non-resonant antennas are inefficient. But the problem isn’t non-resonance, it’s high SWR on coax.

On the other hand, ladder-line does not suffer from high losses at high SWR, so may be effectively used to feed an antenna that may, at various frequencies, present the feed-line with any SWR from 1:1 to ~10:1. So, with ladder-line, you can completely forget about resonance and SWR, until you get to the radio, where you use a tuner to make the match to 50 j0 ohms.

To compare mismatched feed-line losses we have to start with the antenna’s feed-point impedance, and the line’s impedance, then calculate the SWR, and finally, the loss of each feed-line-type at a given frequency and length.

For a worst-case example, feeding a voltage node (like running 40 meters on an 80 meter dipole), let’s say the feed-point impedance is 3500 ohms. With 100 feet of RG-8 coax at 7 MHz, that's a whopping 65:1 SWR, with a total loss of 78%. With 600-ohm open-wire line, the SWR is only 5.8, and the loss is 3%! Then, if we switch to 80 meters, the impedance is 50 ohms, the SWR is ~12:1, and the loss is 7%. In this case, 450-ohm line would be even better, because the SWR only varies from about 9:1 at 50 ohms to 7.7:1 at 3500 ohms. The total losses for 100 feet of 450-ohm windowed ladder-line, at 9:1 SWR, ranges from 5% at 3.5 MHz, to 14% at 28 MHz, and again, that’s at the worst-case mismatch points.

So we see that ladder-line is not only better for non-resonant antennas because of its much lower loss at high SWR, but also because its characteristic impedance places it nearer the center of the antenna's impedance range, from lowest (odd half-waves) to highest (even half-waves).

See also: my feed-line calculator -- you can have hours of fun with that!

Handy formula: VSWR = (1+r)/(1-r), where r = (Zl-Zo)/(Zl+Zo), where Zl=load impedance and Zo=line impedance, in ohms.

Tuner and Balun Loss Myths

Another popular myth is that antenna tuners are very lossy and waste a bunch of power. Baloney! A T-tuner is about 95% efficient, and an L-tuner (like most auto-tuners) is about 98% efficient. If your tuner is getting hot, you definately have something wrong in the antenna system, and are exceeding the design limits of the tuner.

On the other hand, baluns can be very lossy or very efficient, depending on the design and how they are used (or misused). As with tuners, if they are getting hot, they are wasting power, and you either need to change the feed-line length, or buy a better balun. Note that there are many baluns being sold that aren’t even real baluns, like the 4:1 current balun with only one toroidal core. Any real current balun will have two cores, and be well-engineered.

Ladder-Line Myths

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 feeding a balanced antenna, like a center-fed wire. If the power in each conductor is equal and opposite, we have complete phase-cancellation, and thus, no RF radiation. (This is NOT true for off-center-fed antennas, like end-feed, or the various Windom-type feeds, where feed-line radiation is significant enough to warrant a bunch of power-wasting chokes.)
  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 40, 80, and 110 feet work well. A resonant length of ladder-line, just like the shield of coax, will pick up RF (common-mode induction) from the antenna and re-radiate it into the shack. However, while the coax shield is grounded, giving induced currents a place to go, ladder-line is not grounded, so there's no place for induced currents to go, except for reflection, if the ladder-line is near a resonant length. A non-resonant length will present a high impedance to common-mode current reflections. And, as with any feed-line, it’s best to run it perpendicular to the antenna as far as you can so the magnetic fields from each half of the dipole will cancel each other instead of inducing common-mode current in the feed-line.
  3. “It’s too hard to work with! You have to keep it away from metal!” Well, yes, a few inches or so. The general rule is: at least twice the width of the line. It’s easy to make stand-offs from small 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. Like, 8 feet right against metal would be too much at 28 MHz, where you'd have ¼-wave of inductive coupling.
  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 later in this article (brass screws through a plastic window). You could also use parallel coaxes to make your entry, or simply mount your balun outside the wall and come in with a few feet of coax. If your wall is non-metallic, you can simply drill two small (~1/8") holes and bring two #12-#14 wires through, then caulk, and connect them to the balanced output of your tuner with banana plugs. Simple!
  5. “I can’t buy a lightening arrestor for ladder-line!” So just make them yourself, as shown later herein, using sparkplugs.
  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-gauge stranded is much more reliable than the 18-gauge solid line.

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 75% 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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Continued…

130 thoughts on “Ladder Line
  1. OK, I’m sold on ladder line! Problem may be that I live in a mobile home with both metal siding and roofing. My current setup is:

    Coax from the antennas (HF, VHF, TV) passes through a 18″ standoff (made from pvc pipe) then down to drip loops before entering a 14″x14″x6″ plastic utility box. Inside the coax connects to bulkhead type arresters mounted in a grounded copper bracket. Coax to the shack connects to the other side of the arresters and turns 90 degrees before entering a short conduit made of 3″ pvc pipe.

    My tuner is a Palstar AT2-K.

    Looks like I have two options. I’d appreciate your opinion as to the upside/downside factors:

    Work with what I’ve got: run 6-8′ of RG-8 to an arrester and balun in the exterior box, then ladder line out is a gentle curve.

    Old school: Create a non-metallic panel in the exterior wall and run the ladder line directly through. I could mount a knife switch at the entry point and shunt the antenna to ground when not in use. How large should the non-conductive panel be? 16″x16″ is the most convenient size.

    • Howdy Brad,
      I also live in sheet-metal, and have a plastic junction box outside, with a big PVC thru the wall. But I didn’t try to use it as a ladder line termination point because there’s an AC transformer and some HVAC relays in it.

      Work with what you’ve got – the balun and arrestor (well-grounded) in the outside box is much safer, and more RFI-proof.

      If you do bring it in, there’s no need to install a non-metallic panel. I once had mine coming right through the metal trailer wall; drilled two 3/8ths” holes & put vinyl tubing for extra HV insulation, pushed wires thru tubings, then caulked & sealed. Another time I came in with short parallel coaxes. Both worked fine but I didn’t like the lightening hazard, and ended up with a balun outside, with 2′ RG213 to a 6″ SO-239 bulkhead fitting (grounded outside) through the wall, above the tuner, where it’s easy to disconnect (no more reaching behind stuff). Then another short coax to the tuner.

      So it took me 3 tries but I finally got it to where it’s both safe and convenient. I didn’t realize at first that if you bring it in, then the indoor balun, then ground the coax shield side, then the ground has to go back outside. It’s just better if the balun and any lightening grounds are outside, so when you disconnect for a storm your inside stuff is more isolated from any big arcs.

      I wasted money on a 30A DPDT knife switch, then when it came in I saw the connection terminals were like a half-inch apart, way to close to be any good for lightening impulses, so I didn’t use it. They don’t make’em like they used to!

      Just my 2 cents, 73!
      –KV5R

  2. All of these replies have points to look at. I have a tubular tower that is about 41ft high, plan on putting a 80 meter dipole at the top (maybe 130ft on each side) and running ladder line down to the 600 ohm to 50 ohm Balun (bought on ebay years ago, Antenna Products Co, SM-153/N, 2-30mhz 1kw avg 4kw PEP, paid a whopping $25 for it, someone paid much more than this). This Balun case . will be about 5 feet off the ground, coax from it to a coupler (itself in a fiberglass box), from the coupler 50 ohm to the shack. No open feedline inside the metal building I have. I am hoping to get a good almost all band antenna out of this. Any suggestions from you fellows? I have dipoles up there now, one for 80 and one for 40 but the performance isnt as good as I expected.

    • Minimize the length of coax; mount balun on wall just outside of tuner location. Go thru metal wall with bulkhead coax connector (makes a grounding point, plus easy to reach storm disconnect).
      Use a 1:1 choke balun designed for multi-band ladder-line doublets, such as the Balun Designs 1171. A 12, 9, or even 4:1 balun is no longer recommended for LL-fed doublets because at some freqs it’ll present very low impedance to T-tuner, where they are very inefficient. Both Balun Designs and DX Engineering sites have tech articles about this; see also G3TXQ article.
      Expect to have to adjust LL length a few times to make the system matchable on all bands, so start with several feet of slack in ladder line.
      73, –KV5R

  3. All great Info… but… I’m new to ladder. Recently put up a G5RV variation. Installed as near to instructions as possible. Yeah, it’s too low..25 ft. Ends at 12 ft or so. 40 ft ladder drop taped 3 places on the max gain systems fiberglass telescoping pole. Horizontal excess 8 ft from ground attached to a long run of pvc. Then into a 1:1 choke. Then 70 ft of a good rg8. Then into A full power Tentec tuner, AL82, and finally a Orion ll. Antenna will demonstrate in excess of 3:1 with the tuner at the low end of 40 and past midway it is totally UN tunable. Supposedly it should be a no tuner antenna. This GS6 ANTENNA IS A NIGHTMARE. TOTALLY FORGOT IT IF IT’S RAINING. I’m sure I’m missing something. Boneheadsoften do.HELP.. arghhhhh.

    • The G5RV has never been a “no-tuner” antenna, except on 20 meters, where it’s 3/2-wave. On all bands but 20, the SWR on the coax is very high and therefore very lossy. To fix a G5RV, add wire til it’s about 125-130 feet long, then add ladder line til it reaches a 1:1 choke balun at the shack.

  4. This was very helpful, I appreciate it. Probably the best article I’ve seen on the subject. After a long absence I’m getting back into the game with limited antennas due to HOA and considering a multi band attic dipole. My attic is not the most spacious and putting up something like a fan dipole or such, will present many challenges. It sounds like if I can put something up that is at least half wave on 20 (I want to operate 20-10 CW), I should be in good shape if I’m reading this correctly.

  5. Designing a budget hidden “antenna farm” consisting of a hidden loop antenna around the eave of an attached garage. Planning to feed it with ladder line connected to a manual tuner inside the house.

    Problem: the common wall is a fire wall, consisting of plaster on gypsum “button board” on the house wall, and thick stucco on similar button board pm the garage wall. I’ve researched for a solution online and the only thing found so far would be a 2″ or 4″ metallic sleeve filled with intumescent putty (a type of fireblock material) by Unique Firestop (https://www.uniquefirestop.com/store/products/threaded-firestop-sleeve-system/). These sleeves are metal, but if one was used and ladder line were carefully centered before applying the putty, how much signal would be lost?

    My transceiver maximum output is 100 watts. I’ve given up hope of WAS and the Century Club awards; I just want to get back on the air, and do it safely and economically.

    If this idea is totally impractical, my option is run a coax from the shack outside the house, then going along the house wall a foot or so, then back into the garage from outside, and purchasing an automatic tuner to connect directly to the antenna.

    Our club president was the one who cautioned me that just running the ladder line conduits through the wall without fire protection is a no-no, and online research showed me that the building code has upped the requirements in recent years. I plan to consult with him and other knowledgeable members as part of my planning.

    • Have you considered just running a couple small all-thread rods through the wall? Then solder ring lugs on the LL and put between double nuts. Might need to buy or barrow one of these long masonry bits the cable tv guys use.
      Or run a short coax outside to a balun. I recently did the latter, used a Balun Designs 1171 but running a kw now.

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