The “Almost Random” Wire Antenna

I’m still amazed at the success I’m having with my random wire antenna on 80m. Yesterday, I worked a guy who said he was running 500W. He was, of course, 599 here, but he gave me a 589. There’s now no doubt in my mind that a random wire can be an effective antenna.

On the HamRadioHelpGroup mailing list, there was a related discussion about the “almost random” wire antenna. The idea is that some lengths just won’t work well on one or more bands. In general, you want to avoid choosing a length that is a half wavelength, or multiple of a half wavelength of a band that you want to operate.

Tim, N9PUZ notes:

I have used the 49.2 ft (15 Meter) length of wire on vacation with both automatic tuners and an MFJ Model 16010 tuner with good results for 40, 20, 17, and 15 Meter operation. This is not as good an antenna as a dipole or doublet in my opinion but it’s a workable antenna.

Moe, AB8XA, added:

With all the bands we have at our disposal, finding an end-fed antenna length that’s not near 1/2 wavelength on some bands is tough, impossible for me so far. As far as dodging 1/2 wavelengths, 86.9′ may be the best compromise for most bands. Using 95% velocity factor, I find 86.9′ roughly 1/3 λ on 80 m, 2/3 λ on 40 m, 4/3 λ on 20 m, 5/3 λ on 17 m, 7/3 λ on 12 m, and 8/3 λ on 10 m (2.60 – 2.73 λ). But it is exactly 1/2 λ on 60 m, and 0.94 λ, almost 3/3 or 2 half λ, across 30 m, and 1.95 – 2.00 λ, or 6/3 and 4 half λ, on 15 m.

My IC-718 doesn’t have 60m, so slightly shortening the 86.9′ may make it possible to tune 30 m and the lower, CW end of 15 m. But that might bring the lower end of 10 m too close to 2.5 λ.

It appears to me, with an integrated tuner in the radio, which may not have the tuning range necessary for some bands, or even with a wide-range tuner in the shack, the end-fed brings the antenna inside and close to the operator. A remote automatic wide-range tuner, such as the Icom AH-4 or SGC SC-230, between the end of the antenna and lengths of coax and control cable to the shack, appears to me might resolve that problem.

One of these tuners mounted well away from the shack, and close to the ground to feed the required radials, also offers the opportunity to turn an almost all horizontal wire into an inverted-L. From what I’ve seen playing with some modeling software, adding some vertical portion to the antenna can slightly ease the cloud-burning effect of a relatively low horizontal run on lower frequencies, as well as significantly reduce the depth of the nulls of a long horizontal wire on higher frequencies. But I’m sure no antenna expert. It’s always been my toughest subject.

My antenna is 85-ft. long, so I bet I can get mine to load on nearly any band. My next project is to connect it so an SGC-239 automatic antenna tuner that I have and just see what I can do on bands other than 80m.

Comments

  1. http://www.w0ipl.net/ECom/NVIS/random-l.htm

    Thanks, Pat! Click on the link and you’ll find a nifty explanation on why a random wire shouldn’t really be random and a chart of lengths that you’ll want to avoid……Dan

  2. I see no reason at all why a 1/2 wave long wire should be considered bad. In fact I think it is one of the best lengths to use if you can load into a high impedance.

    I have had good luck operating at least several states away on 40 meters using a 1/2 wave long wire and less that one watt.

    BTW a 1/2 wave wire makes it easy to operate without using a ground.

    Nyle Steiner K7NS

  3. Sometimes it is easier to find those who have strong opinions than those who will actually give you good sensible facts when it comes to antennas. Reflecting on this, I decided I had better clarify my statement “easy to operate without using a ground” before I strike someones sensitive spot and waste a lot of heat on this site.

    A better way to say it might be: BTW a 1/2 wave wire antenna gives you a much wider choice of what will work as an effective ground.

  4. py1vhf - Anderson says:

    Guys, when using a tuner like the Icom AH-4 or the Icom AT-120, the manufacturer recomends to stay away from half wavelenght lenghts of wire, because the tuners will “see” a very high impedance and lots of high voltage will result. Also, there is a limit on the impedance these tuners will manage to bring down to around 50 ohms (I think the upper limit is around 8000 ohms).That’s the only reason to avoid half-wave lenght multiples. It has nothing to do with a half-wave antenna being good or bad radiator at all. W0IPL: I think you’ve made a mistake (actually, 3) on your website:
    British use the word “metre”, not “metere”. And you forgot to take into consideration the velocity factor of the wire (which is abt 0.95) in the measurements you’ve made.

    73!

    Anderson – PY1VHF – Macae/RJ

  5. Why is everybody avoiding the 1/2 wave? It is most effective length. It causes smallest interference (TVI) and it needs very much simplified, or almost no counterpoise. Is high impedance the reason? That sure is not the problem after proper transformer is used. Best results ever I had with end fed long wire antenna definitely is 1/2 wave.

  6. Okay, I’m feeling stupid but asking a question is one way to quit being stupid.

    How should a random wire antenna be connected to the tuner or radio?

    Also what is the best way to ground a random wire antenna?

  7. Dan KB6NU says:

    On the SST tuner that I have, there is a two-position terminal strip. The random wire connects to one of them; the ground or counterpoise connects to the other. In my case, I’m using a counterpoise that is approximately 66-ft. long.

  8. Dave KC9TEC says:

    Try the lengths listed below. These are lengths whose multiples were figured out by Ham Universe. Some were were carried out to multiples of 32 just to make sure they are not near any 1/2 wavelength of any one frequency. A good tuner and an artificial ground will put you in business. 73’s and good luck

    The lengths are:

    29 35.5 41 58 71 84 107 119 148 203 347 407 423

  9. Mike Baggett says:

    There is so much misinformation on the web because some folks have not actually tried things but go on what everybody else has said. If someone said 75 years ago you can’t work all bands on an end fed or stay away from 1/2 wavelength then it continues to be touted by everyone from the ARRL antenna handbook to the oldest “experienced” ham.

    Here’s how to get any length of wire over 60 feet long to work any band from 160 to 6 meters. Buy an Icom AH-4 end fed tuner (auto coupler), attach your wire antenna wire to the hot end and run a short wire from ground side to a ground rod or counterpoise wire and enjoy. Get the wire up as high as you can. The AH-4 makes everything equal. I have even been about to tune a 1 foot long wire on 75 meters as long as I have a ground attached (not saying it would be work, but it tunes. With the longer wire it does indeed work.

    ki5so

  10. Does the length of the wire include from the tuner to the mast where it then travels to the other end?

  11. Thanks

  12. My first antenna, errected in haste was a random end fed, joined to an MFJ versa tuner by coax. Several contacts ensued, with good reports. The fourth contact gave me 5/9 then proceeded to tell me that my antenna setup was not a good idea, and would not work very well. This was my first inkling that perhaps the theory did not always tie in with practice. I still hold this view.

  13. I have a Yaesu FC-40 long wire antenna tuner. I have tried every length of wire in the list above. What I really need is a detailed description of what to attach to the grounding lug on the tuner and how to position it. I currently have an 8′ copper ground rod pounded straight into the ground. It doesn’t work worth a crap!

    • I would try just a wire laying on the ground. You could try different lengths. I think that will work better than the ground rod.

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