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For HF operating, I am considering running a ladder line from the ATU just inside a window, through the window (squeezing it between the window and the window frame; not actually through the glass), and out to a dipole suspended outside.

I am interested in all amateur HF bands, 3.5 MHz to 28 MHz, but can absolutely live without 1.8 MHz, and can live without 24 and 28 MHz in a pinch. The idea is to try to avoid having to drill a hole to route a coax cable through. The window frames are made of wood, so coupling should not be a problem there.

I haven't yet considered the exact height and length of the dipole, but the plan is to make it a simple center fed dipole as long and high as I can make it, with a bleeder resistor across the feedpoint to help bleed off static. The ladder line would ideally extend to the feedpoint of the antenna, minimizing the number of joints that could break.

The feed between the ATU and the transceiver would be a short coax patch cable (think half a meter of RG-58 or something like that, mostly depending on what exactly I have in my junkbox).

I have some computer equipment, including a powered 2.1 speaker set and a USB hub, within a meter or so from where, based on my current (very rough draft) ideas, the feedline would pass. I don't need to have the speakers turned on while transmitting, but it would be a bummer if for example the computer starts acting up due to RFI.

Hence my questions (two, but highly related):

  • Am I insane for even considering a setup like this?
  • What do I need to watch out for? Any particular things that can come back and bite me if I'm not aware of them, and how to mitigate those?

Particularly when answering the latter, please consider me essentially a beginner; it's been long enough since I had to actually worry about these things that the things you would mention to a beginner is probably a good place to start.

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    $\begingroup$ I've heard of people doing this without any particular compromise (but I can't answer more completely). You might want to mention whether your window frames are wood, vinyl, or aluminum. $\endgroup$ – Kevin Reid AG6YO Dec 8 '15 at 20:54
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    $\begingroup$ @MichaelKjörling -- I have a similar setup with an 80-meter dipole up about 50 feet (average) and fed with 450 ohm ladder line. I also use a tuner and work 80, 40, 30 meters with ease on the antenna (I work other bands on 20-10 hex beam). However, one difference: I use a 4:1 balun just outside of my room ("shack") and bring Coax into the tuner and then radio. I pass the coax through the wall, not true the window. I built a special box for transferring coax and other connections through the wall itself. $\endgroup$ – K7PEH Dec 8 '15 at 21:33
  • $\begingroup$ @K7PEH Yeah, something like that is on my list of someday-projects, where it has solidly remained for quite some time. This would seem to be a way to get on the air with a relative minimum amount of hassle, and actually be something I could fairly easily pull off. $\endgroup$ – a CVn Dec 8 '15 at 21:43
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    $\begingroup$ Feed the "Ladder Line" "S" between the upper & lower windows (where window locks are usually located). That avoids sharp bends & rain water drips off without entering the house. Add a power line choke close to your computer. $\endgroup$ – Optionparty Dec 8 '15 at 21:51
  • $\begingroup$ @Optionparty I'm not sure what you are referring to. I have no "upper" and "lower" windows, but obviously when running the ladder line I'd do my best to ensure that water has a chance to drip off outside the house rather than being routed inside! $\endgroup$ – a CVn Dec 8 '15 at 21:53
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Am I insane for even considering a setup like this?

No.

What do I need to watch out for? Any particular things that can come back and bite me if I'm not aware of them, and how to mitigate those?

Avoid running the ladder line parallel to any conductive material for any "larger" fraction of your shortest operating wavelength. By "larger" I guess 10 percent or larger.

Also, try to avoid 90 degree bends in the ladder line or loops.

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  • $\begingroup$ Keeping possible coupling lengths to below 1-1.5 meters or so should be no problem at all. $\endgroup$ – a CVn Dec 8 '15 at 21:45
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I haven't done this myself, but I've heard about people doing it without trouble.

You specify that your window frames are wood, so that's not a problem. However, modern insulated (double-glazed) windows may have metal as part of the seal on the glass (it would be visible looking in through the glass). If you have this, make sure the ladder line doesn't run parallel to the frame on the inside or outside.

Twisting your ladder line also helps reduce radiation and coupling to nearby metal.


The second issue is interference with the speakers and other electronic equipment. (Even if the effects are minor, you'll likely want to get them entirely cleaned up if you get into digital modes!) In priority:

  1. Make sure that you have a suitable balun either built in to, or in addition to, your antenna tuner. (I've heard rumors that some tuners with balanced outputs have baluns that aren't actually very effective.)

  2. Ground the antenna tuner: connect its ground terminal to the shortest path to earth ground you can get. If everything else is perfect, this is unnecessary, but it will help. (Note: All else being equal, making only this connection likely decreases lightning safety. Either do your research for a complete grounding system, or disconnect your antenna, and the additional ground, for any storm.)

  3. Finally, if you can separate equipment, do so. (Move that USB hub!) Try to have one side of the room for your digital signals and the other for your RF signals.

  4. Add ferrite chokes to all the cables in the room/house. This is a last resort because it is better to stop the signal getting out (of your feed line) than to stop it getting in (to everything else), but it may be necessary if you are getting interference not from your feed line but your antenna, i.e. the signal you're actually intending to transmit.

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  • $\begingroup$ Unfortunately, #3 (one side of the room for the computer and the other for the radio) is not really an option in my case, at least for the time being, for reasons unrelated. The USB hub is movable, but having it where it is is a great convenience... When you say ground in #2, I take it you are referring primarily to DC ground? $\endgroup$ – a CVn Dec 8 '15 at 22:04
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    $\begingroup$ @MichaelKjörling I don't know what you mean by “DC” ground. The purpose of this ground connection is to give any stray RF a place to go other than through the ground/shield paths of your other equipment. $\endgroup$ – Kevin Reid AG6YO Dec 8 '15 at 22:10
  • $\begingroup$ Disconnect that ground, too. Two grounds and zero antennas is still a recipe for lightning damage. $\endgroup$ – Phil Frost - W8II Dec 10 '15 at 19:09
  • $\begingroup$ @PhilFrost Added. $\endgroup$ – Kevin Reid AG6YO Dec 10 '15 at 19:19
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In theory, any material with a relative permittivity or permeability in the space within a few multiples of the conductor spacing of the ladder line will alter the characteristic impedance of your ladder line.

Will that be a problem? It's not likely. You already have a tuner so you are equipped to deal with whatever impedance may appear at the end of the feedline.

The window frame might be lossier than air, but since the transmission line is running through it for only a very small distance (relative to HF wavelengths), it's unlikely to have any practical consequence.

But don't just believe me, try science! You can use your radio's S meter to measure the power received from a signal. If the window frame is introducing loss, you should see that when the window is shut on the feedline, the S meter indicates less received power, because some of it is being lost in the window frame. So find some CW or AM station (because these modulations, unlike SSB, have a more or less constant power) and compare for yourself the received power under various conditions.

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  • $\begingroup$ I probably will try science once I have this set up, but the problem with that is that I pretty much have to commit to the setup, including doing most of the work, before I am able to do such an experiment. I'm hoping to at least work out most of the kinks before doing all of that work. $\endgroup$ – a CVn Dec 19 '15 at 13:13

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