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I'm finally getting to the point of hopefully putting up a HF antenna. The idea is to start with a simple, straight wire dipole using trees as support points. (No traps or coils.)

However, with the layout of my property and the location of the trees thereon, putting up a fully balanced antenna might be difficult.

I'm not aiming for an antenna that is resonant on any particular frequency to begin with, so will be using an ATU in any case. I'm also going to be operating on most of the HF bands, so the feedline will essentially be random length at least on some relevant frequencies.

I'm aiming more for local-ish contacts than DX; with what I'm planning to do right now I won't really be able to get the antenna up high enough to get the takeoff angle down far enough for DX anyway.

The general idea for station setup is to have the transceiver, then 50 ohm coax to the ATU (which in turn is just inside the window, and which has a built-in 4:1 balun), then attached to its binding posts balanced ladder line (through the window) which eventually splits into the two legs of the antenna to actually radiate the signal. There will also be a bleeder resistor somewhere along the length of feedline, to help reduce the buildup of static, and a physical/electrical disconnection point between the bleeder resistor and where the feedline enters the house (allowing for true electrical disconnection of the antenna when I'm not on the radio). I'm aware of the need to keep balanced ladder line away from other conductors that it could parasitically couple to (as e.g. Hamsterdave illustrated just recently, though perhaps not quite as extreme).

With such a setup, which approach is likely to lead to better operating results, as well as less problems with RFI and friends?

  • As much antenna wire in the air as possible, disregarding the relative feedpoint, possibly leading to an off-center-fed antenna?
  • Keeping the antenna as balanced as possible, even if this means less wire in the air?

Bonus if answers also touch on how the choice is likely to impact antenna tuning (it'd be nice if I don't have to retune every 10 kHz).

The ambient HF noise level, as far as I have been able to determine by completely unscientific testing, is quite low, and I'd love to be able to make the most of that.

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I think in practice you'll find it doesn't make much difference as long as there's a common mode choke or "current balun1" at the feedpoint. In fact, if you get it off-center in just the right place you can get an impedance around 200 ohms on several bands. Even though you'll be using an ATU, there's a limit to how much mismatch they can tune out, and feedline losses go down with decreasing SWR.

When the feedline isn't in the middle of the dipole, the impedance between the common mode of the feedline and the two legs of the dipole are unequal, so you end up with common-mode currents on the feedline. This isn't much different from the situation with a coax feedline. Just use a choke.

The balun in the ATU does take care of interfacing with the ladder line, but it doesn't do anything about the feed arrangement: you still need a choke up there if you want to prevent common-mode current on the feedline, thus effectively making the feedline part of the antenna. At 100W or less you'll probably not get any RF burns, but it does mean your antenna is within a few feet of noisy electronics like computer monitors and switching power supplies in your shack. Not the best for receive performance.

A couple more points of note:

If the intention in disconnecting your antenna is to protect from lightning damage, you'll need more than a little gap in a switch to do it. See W8JI on grounding systems (The "Isolating or Disconnecting feed lines" section in particular) and How can I protect equipment against a lightning strike?

Your antenna setup is not going to have any effect on RFI with your neighbors except to the extent that you radiate less energy (not usually desirable in an antenna), put it farther from the neighbors, or direct the radiation pattern away from them. Feeding the dipole in the center or not will make no difference.

Once you have a 1/2 wavelength of wire in the air, more isn't really a benefit.


1 or is it a balbal in this case? Or a unbal? Amateur terminology is so confusing.

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  • $\begingroup$ Are you suggesting an off-center feedpoint plus a balun (or some such) near the point where effectively the feedline splays into the two legs of the antenna? $\endgroup$ – a CVn Jul 29 '16 at 20:43
  • $\begingroup$ As for "disconnecting your antenna is to protect from lightning damage, you'll need more than a little gap in a switch", I didn't go into that in this question because I didn't feel it was relevant to the question, but the idea is to have two junction boxes with a length of disconnectable feedline in between (the antenna feeding into one of them, and the transceiver/ATU feeding into the other), disconnecting that length of cable when I'm not actively using the radio. Not just a puny little switch which might at best have a breakdown voltage a fraction of that potentially seen. $\endgroup$ – a CVn Jul 29 '16 at 20:43
  • $\begingroup$ @MichaelKjörling Automate your disconnectable feedline! (from) $\endgroup$ – Kevin Reid AG6YO Jul 29 '16 at 21:13
  • $\begingroup$ “Having a balun in the ATU isn't going to help too much” — Don't you want a balun in both places for this configuration? Unbalanced coax from transceiver —ATU→ balanced high-SWR feed line —feedpoint→ unbalanced antenna; that's two balanced/unbalanced transitions. $\endgroup$ – Kevin Reid AG6YO Jul 29 '16 at 21:16
  • $\begingroup$ @KevinReidAG6YO you are right. I've edited to make it more specific. $\endgroup$ – Phil Frost - W8II Jul 29 '16 at 23:08
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I haven't been in your exact situation, but I have friends who have, and I would suggest that the answer is it depends. There are many variables involved. One important variable is the quality of your balun. Another is the kind of contacts that you'd like to make: local, DX, or both?

There's certainly nothing wrong with asking here for suggestions, but a big part of the traditional amateur radio experience is experimenting with antennas to see what works best for you. I suggest that you put up a dipole (it would actually be a doublet if you don't plan on using it only near its resonant frequency), or an unbalanced doublet, in such a way that you can easily add or remove wire later.

Upon reflection I'll venture an opinion: I would say that the antenna being slightly unbalanced, with the feed point somewhere in the middle third of the antenna, would be unlikely to cause you problems. Many people run antennas more unbalanced than that, but then the balun becomes more critical, so I wouldn't recommend a more unbalanced antenna for starters.

I also suggest that you pay attention to mechanical details. Most importantly, try to keep the ladder line as far away from metal as possible. You'll want to put up your antenna so that you can easily bring it down temporarily and put it up again; perhaps have the ends of the antenna attached to halyards, i.e. ropes attached to pulleys. Some sort of strain relief so that the wire doesn't get snapped in a storm would be a good idea.

I think you'll enjoy the process of experimentation much more than just accepting someone else's idea of what antenna would be best. Have fun!

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  • $\begingroup$ There are a few complicating factors here, such as having the balun inside the shack and running a balanced feedline all the way to the ATU. And sure, I could just try, and see if the neighbors start making unhappy noises (there's no guarantee that I'd be the one to notice RFI first, particularly since I have very little analog equipment); or I could ask for other peoples' experience first, and take that into consideration before I spend time and neighborhood good will. $\endgroup$ – a CVn Jul 29 '16 at 19:54
  • $\begingroup$ @MichaelKjörling, just because an antenna is unbalanced doesn't necessarily mean that the antenna will radiate on the wrong frequency (RFI). In order for significant RFI to be radiated I would think there would have to be a fairly severe RF-in-the-shack problem. If you were to run about 100 W from a modern radio with a reasonably good balun, like the one that comes with the ATU, then I would be amazed if you were radiating any RFI that the neighbors could detect. Sometimes neighbors blame hams for all sorts of imagined RFI once they see an antenna, but that's a different problem... $\endgroup$ – rclocher3 Jul 29 '16 at 20:19
  • $\begingroup$ If the ladder line were unbalanced, then the ladder line would radiate as part of the antenna, but that's not necessarily a bad thing, and it doesn't automatically mean that the antenna would radiate on the wrong frequency. $\endgroup$ – rclocher3 Jul 29 '16 at 20:22
  • $\begingroup$ Now I'm a bit confused. Is your answer "try putting up as much wire as possible and it'll likely work well, but be prepared just in case it doesn't", or is it "it's better to try to keep the antenna roughly balanced from the beginning, to avoid problems"? You may also want to see my hopefully clarifying edit to the question, if you haven't already. $\endgroup$ – a CVn Jul 29 '16 at 20:26
  • $\begingroup$ I would say to start with an antenna that has as much wire in the air as possible, as long as the antenna is roughly balanced with the feed point somewhere in the middle third of the antenna. Then tweak it and see what happens! $\endgroup$ – rclocher3 Jul 29 '16 at 20:29
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I would prefer balanced dipole. That would solve some issues by itself.

With unbalanced antenna you would have to use chokes to fix symptoms like RFI, but does not fix unbalanced behavior of antenna so it is better to avoid need to use them.

Check Why aren't there baluns that do BOTH balanced/unbalanced transformation and common mode current attenuation? for some explanation about chokes.

If you plan is to use single antenna and ATU, then I guess using as much wire ass possible is more viable option (I still prefer balanced setup, or closed loop). You will have huge looses anyways so more wire will at least compensate, and radiate more efficiently energy that makes into it.

As already suggested, it is possible you will not find solution in first strike. It needs experimentation.

I would suggest reconsidering idea of using single antenna and think of some kind of multiband antennas or combination, dipole for lower bands and vertical for higher bands.

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  • $\begingroup$ Please clarify your answer. What is “unbalanced behavior of the antenna” and why is it bad? $\endgroup$ – Kevin Reid AG6YO Jul 30 '16 at 14:29

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