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I am considering many possible doublet antenna scenarios for a multi-band antenna (80 meters to hopefully, 6 meters) customized to my specific home situation.

Everything is a compromise. I will be using a 450-ohm windowed ladder cable in several scenarios, but I keep running into a lack of clear facts surrounding using a 450-ohm ladder line. For example, a repeated "consensus" is that the cable should be away from the ground by several widths of the window, not on the ground or buried, it shouldn't ever be close to other metal structures, and that it easily 'radiates.' Unfortunately, several Elmer's out there claim much of that so-called "conventional wisdom" is a bit overblown and overstated.

Can anyone direct me to some legitimate research (a bit less anecdotal) that has been done on the 450-ohm ladder line? I don't mind conventional wisdom, but I can tell that much of it is just "parroted" from someone else they heard from or some YouTuber rather than based on genuine hands-on experience.

Anyways, I would love to read some facts if anyone out there can direct me. I don't mind experimenting, but I'd prefer not to start from scratch if I don't have to. Thanks in advance!

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  • $\begingroup$ Not that it matters, but I'm guessing that this is actually 420 Ω line. $\endgroup$ Commented May 22 at 21:51
  • $\begingroup$ The more that the conductor diameter is increased, the lower the loss. In free space, almost all of the loss in transmission lines are I²R losses in the copper wires. $\endgroup$ Commented May 22 at 21:54
  • $\begingroup$ You will find Uncle Elmer, who is a parrot. They keep repeating the same lie. $\endgroup$
    – Dereck
    Commented May 22 at 23:59
  • $\begingroup$ @Dereck What lie? $\endgroup$ Commented May 23 at 16:34
  • $\begingroup$ You said yourself Uncle Elmer has confused and overstated things. That is because most do not know what they are talking about. They keep repeating the lie they were taught 40-50 years ago. $\endgroup$
    – Dereck
    Commented May 24 at 20:40

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a repeated "consensus" is that the cable should be ... not on the ground or buried

This is an accurate statement. Laying the cable on the ground, and especially burying it, is bad.

  1. The earth is lossy and partially conductive.

  2. The earth will greatly affect the impedance of the line.

That's why nobody buries ladder line. If you need to bury a feedline, use flooded coaxial cable.


You shouldn't even put ladder line in a buried plastic pipe. The EM field surrounding it is likely larger than a reasonable size pipe, even if you centrally support it inside the pipe.

This comes from almost 50 years experience as a ham, and reading relevant info from many technical gurus smarter than I am. Sorry if it seems anecdotal. :-)

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    $\begingroup$ Excellent points. Ladder line characteristic impedance is 'more sensitive' and more easily disrupted compared with a "closed coax". This makes so much more sense. I'm going to run some empirical tests on long ladder lines. I suspect these kinds of tests have been run in the past - I just can't find them). Thanks for making these points! $\endgroup$
    – Michael
    Commented May 23 at 14:32
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Here's some theory as to why this matters...keep this in mind and decide for yourself when you should worry.

All transmission line (coax too, not just ladder line) works by forming opposing magnetic fields between the two conductors. In all transmission lines, this works best when the two fields are equal and opposite and thus cancel, preventing signal from leaking out of the line. (With coax, it's still possible to mess this up, but it's much harder.)

With ladder line, surrounding conductive objects, including parallel metal and conductive earth, the fields in the ladder line can interact asymmetrically with the external objects and imbalance the line if the external conductor is too close. (How much this matters with the ground depends on how conductive it is.)

This can be somewhat mitigated by twisting the ladder line, so that the intruding effect is now symmetrical, affecting both wires in the transmission line somewhat equally. The right density of twists can effectively reduce the distance conductive objects must be separated from the ladder line.

It's not metal objects that matter, but long parallel metal objects.

It's not mere ground that matters, but conductive ground.

The degree to which an object has a long segment parallel to the ladder line and how conductive it is to RF fields affects how much this matters and how well the twists in the ladder line will mitigate it.

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  • $\begingroup$ Thanks for your accurate reply. To advance this further, assume the only variable in question is whether the balanced feed can be on (or in) the ground. Assume a vertical antenna (80m-10m), where the ground is vital to the antenna circuit. Per theory, we are primarily concerned with ground signals that might create an "unbalance" in the two wires of the feedline. It seems logical that long wavelength signals won't "imbalance" the lines, given the rail-rail distance of the window feed is only an inch or so. Under this situation, am I missing another reason not to bury the balanced feedline? $\endgroup$
    – Michael
    Commented May 22 at 15:45
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    $\begingroup$ The other answer has a very good point. The windowed ladder line has windows for a reason. Removal of that small amount of plastic tweaks the impedance. So now you put a bunch of dirt that is more conductive than the plastic near the ladder line and it's going to totally throw off the impedance. It doesn't matter how balanced it is if the impedance is wrong. $\endgroup$
    – user10489
    Commented May 23 at 5:05
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    $\begingroup$ Note that a few bumps on the ground isn't going to mess up the ladder line... it's when you change the dielectric constant of the material near the line for a significant distance that it matters. Burrying it is about the worst thing you could do short of wrapping it tightly around a steel pipe. $\endgroup$
    – user10489
    Commented May 23 at 5:28
  • $\begingroup$ Ahhhh... very nice!! This makes sense to me. We are saying that the ladder line is more sensitive to environments because it is too easy to modify the effective characteristic impedance of that line. Long swaths of nearby conductors, "Earth," and moisture easily fall into that category. Putting the ladder line in larger PVC (if buried) might be 'better' if there were no leaks into the PVC. But, that seems unrealistic in the long term. So - armed with this - my next plan is to confirm all this by running characteristic impedance tests on ladder lines to measure this impact. THX! $\endgroup$
    – Michael
    Commented May 23 at 14:27
  • $\begingroup$ The PVC itself will change the impedance of the ladder line. It's just not a good fit to burry it. Use the right tool for the right job.. You could suspend it in the center of, say, a 2ft diameter pipe. Or I know, you could use a metal pipe instead of a pvc pipe, and suspend a single conductor in the center of it. Or you could just buy some coax. $\endgroup$
    – user10489
    Commented May 24 at 1:27
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Mike, allow me to take a shot at this. Not much theory, just some common-sense electrical facts. You do not want to run a ladder line near dirt or anything metallic. The ladder line is a Balanced transmission protocol, unlike a coax, which is a ground-referenced protocol. If you come close to dirt or metallic objects like structures, it will couple energy into the ground and throw off the balance. When you throw off the balance, you now have common mode currents flowing; the current in both conductors is not equal anymore, and the ladder line will radiate.

Doublets make fantastic antennas if you can get one up uncompromised. Perfect for field days, find suitable trees, string them up, and there are no compromises. The tree supports the ladder line to hang freely in the air. It is challenging to do from inside your home. It would be best to have a tree or two or something like a wooden or fiberglass pole in the right place. I had a contractor plant me a 60-foot utility pole outside the shack and use a couple of trees for end support. Once support and routing are worked out, the next challenge is getting how you will penetrate the outside wall without compromising the feed line.

You have two options to choose from. I used a short coax from the antenna tuner through the wall to a 4:1 current balun outside to transition to the ladder line. The second method uses two short pieces of coax to transition through the wall, as shown below. I will stop here and share this link with you, where the diagram came from. It contains a lot more information you may find helpful. Doublet Antenna

enter image description here

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  • $\begingroup$ Thanks for the link, Dereck. The double coax through the wall (with a tuner on the inside) is something I hadn't seen before. $\endgroup$
    – Michael
    Commented May 25 at 0:45

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