Building a 40m (7MHz) horizontal delta loop

Over the last few weeks I’ve spent quite a lot of time reading about different options for wire HF aerials and one kept coming back into my head as being something I could easily try at this QTH – A full wavelength horizontal ‘delta’ loop for 40m.  My garden is the right sort of size to make this kind of aerial and with the available support I knew I could get it at the right height to take advantage of NVIS propagation.  I really like the idea of being able to put a good signal on 40m into the whole of the UK and a large chunk of Europe.

I knew it would be quite straightforward to do this, the far end would be supported by a rope from the top of the 20ft pole I have mounted at the end of the garden and I could use a couple of screw in insulators on the eves of the house spread as far apart as possible for the other two anchor points.  There are a three common ways to feed such a loop, either balanced feeder back to a tuner, by using a measured quarter wave stub of 75 ohm coax or by using a 4:1 current balun and 50 ohm coax into the shack.  I chose the latter because the only balanced feeder I have is currently at the Martello Tower and I had a 4:1 current balun I recently bought from M0CVO Antennas handy.

The screw in insulators I used are more commonly used for electric fences but they’re ideal for aerial supports.  I had these from my original long wire installation so it was a simple matter to unscrew them from the top of the fence at the bottom of the garden and relocate them to the side of the house.

Electric fence insulator

Electric fence insulator

At the top of the pole I’ve got a pulley I bought from a local boat chandlers and through that is a run of rope which ends in a standard dogbone insulator of the kind one can pick up from any radio rally for a pound or so.

Dogbone insulator

Dogbone insulator

I used flexweave copper wire, bought at a rally for the actual aerial itself and cut a length to around 45 metres which I knew would be too long for the loop but it gave me the flexibility to be able to shorten it to the correct length.

Once everything was in place it was a simple matter of attaching the coax to the balun and then adjusting the aerial until it matched.  I used an MFJ-269 to check it and trim the wire – Once I’d shortened the wire by around 1.5 metres I got a perfect match on 40m and was very pleased to see that I can now operate on the entire band with an SWR of <1.3 without the need for an ATU.

As a bonus it also tunes the whole of 20m with an SWR of <1.8, 15m with an SWR of <1.5 and on 10m it’s <1.2 in the SSB/CW section of the band.

My 40m delta loop installation

My 40m delta loop installation – Click the image for a larger version

Because the loop is so new and conditions have been so poor on HF over the last week I’ve not really had a chance to test it thoroughly yet but my initial impressions are good.  I’ve had QSOs out to over 850 miles already using it with good signal reports each way.

I’ve had some modelling done of the radiation pattern of the loop by Martin, G8JNJ and I’m very pleased to be able to post those models here.  As can be seen, it has a fairly good omni pattern on the HF bands with not too many deep nulls and some gain at low ‘ish’ elevations.  The plots show that it should have very good NVIS performance on 40m and that’s what the aerial was designed for so I’m happy.

North is at the top of all the plots.

40m Loop Azimuth

40m Loop Azimuth

40m Loop at 10 degree elevation

40m Loop at 10 degree elevation

40m Loop at 20 degree elevation

40m Loop at 20 degree elevation

40m Loop at 30 degree elevation

40m Loop at 30 degree elevation

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  1. Hello Keith, I use a 80m horizontal loop in winter and have good results as well on all bands. Especially NVIS is great. 73, Bas

  2. I’d be interested to see how an 80m loop would work here, it would have to be a square and I’d have to put a couple of coils in the corners to get the full length of wire out. I might have to do this because I had a quick try a couple of days ago and couldn’t persuade the MFJ ATU to tune the loop on 80m and it’s a band I do want to be able to operate on.

  3. Hi Kieth, interesting about the loop, I built one for 10m and it worked, at least out to 5 miles! As 10m might be coming to life, I shall have to put it up again. The whole 40m loop is a bit of a no-go here due its visual impact and my wifes opinion!


    1. 10m is one of those bands where when it’s open, you can work the world on a bit of damp string, much like 6m. I reckon that if you put it back up again that you’ll do much better than 5 miles with it Scotty – My indoor 6m dipole is rubbish when the band is closed but when there’s some Es kicking around I’ve worked over 1,100 miles using it.

  4. Hi,
    Nice clear plan drawings. I put a Delta Loop (skyloop) up about 2 moths ago using exactly the same configuration as yourself. It works great and the best thing of all, it works well at low height. My one is up at 7.5m agl, (1:4 voltage balun & 1:1 air cored current balun).
    Nice one. If you manage to get your Delta set for 80m I would be interested in how you do it and what sort of results you get.
    Cheers, SV0XBU

  5. Paul Collins M0BSW

    This is exactly the same amount of room I have here at my location, so just got to have a go at this one,
    Paul M0BSW

  6. Hi Kieth, interesting about the loop, tks for share!!
    73` from Jorge,LU8HRW

  7. Keith:
    I’m going to try this, since my zig-zag long wire (tuned with an ICOM-AH-4 tuner) could easily be reconfigured to a horizontal loop. How does the loop perform on 80 meters?
    The dimension of my loop would be roughly 80′ x 80′ x 40′.
    Thanks, Tom NY2RF W. Palm Beach Florida

  8. Hey Tom,

    With those lengths you won’t have a full wavelength out, 200′ of wire works out at about 60m so unless you add some kind of loading, it won’t resonate on 80m. If you can get another 60′ of wire up then you’ll have a full length loop on 80m and it should work well.

    An ATU will probably match your 200′ of wire to 80m but I can’t comment on the performance – A full wavelength without a tuner will obviously work better than being a bit short and using a tuner. Experiment, it’s what the hobby is all about 🙂

    73 Keith.

    1. Thanks, Keith, so much. I’ll try it in the spring cleaning tasks. DE NY2RF

  9. Hello from Sweden. I have limited space in my back yard so I will try this one with 40 meter as “base band”. The dipole I tried did not work out so well, neither did the windom. Thanks for the detailed description, It will make my trials so much easier.
    73s de SM3TTZ / Pär

    1. Hi Pär,
      Good luck with it – I still think it’s the best aerial I’ve had her for 40m and if it was’t for the fact that my mast is really in the way now, I’d hang another one tomorrow.

      73 Keith.

  10. Im thinking of trying a Delta loop in horizontal 1100ft length and going to be
    longer a bit going to the feed point since my 5 acre lot is long rectangle shape.
    I will feed it at that point with 4:1 balun.
    It will be something like this guys.

    Im going to use on all bands. Will see how it goes.

  11. About 14 months ago, I installed a 40m horizontal delta loop at a 2nd home in Florida. This was my first experience with a loop. I fed it with a homemade 4:1 balun and RG-8X. I was surprised at how well it performed at only about 15 ft high. I worked great DX in Europe and South America. I recently installed another 40m horizontal delta loop at my main QTH in Ohio. Its height is roughly the same, but I am feeding it with 300 ohm balanced line. Its performance is similar to the loop in Florida. These are the best antennas I have ever used, even though they are lower than all of the others (the others were 80m dipole, G5RV, end-fed random wire, and inverted L). It’s hard to explain the performance; but it’s partly due to a better signal to noise ratio on receive.

    1. Hi Mark.
      I really miss my 40m delta loop. When I put the mast up, I just found that the interaction between the mast and the loop was too great and the loop didn’t work very well. It was also a real pain to lower the loop whenever I wanted to do anything on the mast. If I could find a way to re-hang it then I’d be a very happy ham.
      Like you, I still think the loop was the best aerial I’ve had on 40m. I’ve tried inverted Ls, long wires, OCFDs and even a single band dipole but the loop beat them all.
      73 Keith.

      1. What most of us hams lack is the ability to do side-by-side comparisons of antennas, either because of insufficient space to erect multiple antennas, or because of the interactions among the wires. I did a “well controlled” study of the effects of radials on a 1/2 wave vertical (for 10m) a long time ago. I used another 10m vertical antenna on the opposite end of my roof as a “control.” I could take down the test antenna and install or remove the radials, but the process could take three hours or more. During this time, propagation conditions could change a lot. But by having a control antenna to compare to, I could tell if the radials were significantly better or worse than the control. I didn’t have to be concerned that any differences observed were due to propagation changes. Unfortunately, I don’t have the space to do similar comparisons on the lower bands.

  12. I have 4 wire antenna’s and a large area to work with and very high gum trees.
    My antenna’s are an 80 meter loop at 65 feet, a ZS6BKW at 60 feet,, an 80 meter dipole at 60 feet, and an 80 M OCF at 60 feet, i am able to switch between them all, overall the 80 meter loop is the best performer, quieter on receive and gives me SWR’s below 1.15:1 or better on the SSB segments on 80,40, 20, 15 and 10 meters using a mast head tuner..
    My ZS6BKW is the next performer with slightly better signal out on particular frequencies, notably 40 and 15 but noisier on receive than the loop,
    I do use a Daiwa T type tuner on the ZS6 the 80 dipole and the OCF, it easily reigns in low SWR’s.on most bands I operate on.
    My 80 meter dipole with 1:1 current balun certainly works very well for NVIS and out to 1400 Klm’s, The OCF with 4:1 balun I’m not sold on but it does get out but under performs in my situation in comparison with the other antenna’s.overall.

    1. Hi Ross,

      I’ve tried an OCFD dipole multiple times now, using different lengths, different feed points and different baluns and I’ve never found a configuration I’m happy with.

      The 40m delta loop is still the best aerial I’ve used for inter-G and western EU QSOs, the height was perfect for NVIS and when I had it up, we were at the peak of the solar cycle and there were special event stations on 40m every single weekend. They all had huge pileups and I broke every single one of them either on first or second call. It was a fantastic aerial!

      73 Keith.

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