Some antenna tuners claim to match any “random wire” to any HF frequency. Can one really use a random wire as a practical antenna system?

From everything I have heard, the resonance of the antenna (length, material) is what defines its performance on a given frequency. Is this only a minimalist emergency use concept, a fraction of a watt being better than no antenna at all?

up vote 10 down vote accepted

Yes, a random wire can be a practical antenna. Anything conductive can be loaded up. Somethings work better than others. But if you want to play around, there's no reason the antenna has to be an "antenna".

There are, of course, some drawbacks:

  • You must have a tuner.
  • You might not get a match on every band you'd like to work.
  • For efficiency, you need a counterpoise, an insulated wire that attaches to the ground of your tuner. Ideally, this is 1/4 wave long at the lowest band you'll operate on. Note that this is not a radial, so it doesn't have to be straight.
  • The "antenna" starts at the back of your tuner (i.e., in the shack), so power levels must be low unless you like living in an RF fields and collecting RF burns.
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    I think there are quite a lot of ways to make a counterpoise other than what you describe. Without a counterpoise, Earth will probably be the counterpoise, so anything that replaces this with a less lossy path could be called "a counterpoise". – Phil Frost - W8II Nov 14 '13 at 17:36
  • @PhilFrost oh absolutely, I was just giving a for instance. This is necessarily an "anything goes" type of situation. Try it and see what happens. – WPrecht Nov 14 '13 at 18:05

It is amazing what can be used for antennas. On a lark, I tried what I read in a club newsletter once and connected a tuner to my downspout. I was able to work south americans on 10 meters!

A random wire is just that - a random length of wire, possibly thrown over a tree limb or whatever gets it as high as possible fed with a tuner.

You're right - it won't be resonant, and the tuner is just 'making the radio think' the antenna is resonant, but it could be very effective!

The best part is experimenting - try it out!

I think instead of saying that you can "load up anything conductive" or that the tuner makes the transmitter think that the random wire antenna is resonant, it's better to say that the tuner converts the impedance at the end of the random wire to 50 ohms, which is the impedance that the transmitter wants to see.

Having said that, what AB3RY says about random wires is correct. I used a random wire antenna on 80m for a while. The tuner was on a window sill in my shack, and I could run up to 25W before the RF in the shack got to be too much.

The reason to have the tuner in the shack is so that it can be easily adjusted, BUT if you had an automatic antenna tuner and could locate it some distance from the shack, then RF in the shack would not be such a big problem. Several companies make remote antenna tuners that come in weatherproof enclosures.

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    I think this is erroneously conflating two issues. Moving the tuner to the feedpoint will decrease the VSWR on the feedline, but it will do nothing to reduce the common-mode currents that are responsible for "RF in the shack". – Phil Frost - W8II Mar 4 '15 at 16:12
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  • Sure it will, because it will move the radiating portion of the antenna further away from the shack. – Dan KB6NU Mar 5 '15 at 17:33
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    If I install a vertical with no radials, should I expect a lot of common-mode current on the feedline? Does that change if I put a tuner at the base of the vertical? The only way to reduce common-mode current on the feedline is to have some other counterpoise with a significantly lower impedance to those currents. The common-mode currents exist not because the antenna is mismatched, but because the feedline is the counterpoise. Tuner or not. – Phil Frost - W8II Mar 5 '15 at 20:22

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