Speaker Wire Delta Loop

Here’s an example of what can happen when you have a hunk of cheap wire and a little too much time on your hands.

Years back, I did a write-up on a simple, random wire antenna made from a 50-foot roll of speaker wire from a local dollar store. I nick-named it the Dollar Store Special. I had a similar roll of wire in my junk box, so I set out to see if I could build another useful portable antenna from it.

This time out, I wanted to build something more elaborate than a random wire. After some sketching with a pencil and paper, I came up with this simple portable delta loop.

There are certainly better ways to construct a delta loop. However, I just wanted to see if I could build a functional antenna using only cheap speaker wire. So, with that in mind, here’s how I did it.

The Design

The antenna I built was inspired by a portable delta loop designed by Doug DeMaw, W1FB. [1] Doug’s multiband delta loop was designed for the 40M band and used a 300-ohm balanced feeder. 

According to Doug’s book, this type of antenna should work well on the fundamental frequency and higher. For the next band below the fundamental, he suggests connecting the feeder wires together and using it like a random wire. I figured I’d just try loading it up as is to see what happens.

Given that I constrained myself to a 50-foot roll of speak wire, I scaled my antenna for the 20M band. Using the formula, 1005 divided by the frequency in megahertz, I calculated a total length of 71 feet (21.6 meters) for the center of the 20M band. That would leave some of the two-conductor wire for an improvised balanced feeder.

Feeding the delta loop in a corner (with the apex of the loop pointing up), gives the antenna vertical polarity with a low take-off angle.[2] As with most antennas, higher is better. However, this antenna is still quite useful at practical heights in the field.

Since a tuner will always be necessary, I expended no effort trying to optimize the design.

Construction

Schematic diagram of the delta loop antenna
Schematic diagram of the delta loop antenna

If you’re a visual person like me, refer to the diagram to help make sense of the directions below.

  1. Measure off 35.5 feet from one end of the speaker wire. Place a small zip-tie around the wire at this point.
  2. Separate the 35.5-foot end of the speaker wire into two separate wires.
  3. Strip and solder the loose ends of the 35.5-foot wires together. Put some electrical tape or shrink tubing over the splice.
  4. Make 3 small loops in the wire, as shown in the diagram. You can see an example in the accompanying photo. These are going to be the attachment points. I used some Goop® adhesive on the zip-ties to help hold things in place.
  5. Finally, install some spade terminals on the ends of the shorter conductors. These will be used to attach the antenna to your tuner or balun.
Example attachment point. This is the feedpoint of the antenna. The two wires to the right are part of the loop antenna, while the wires towards the bottom serve as the balanced feedline. I used some Goop® adhesive on the zip-ties to help hold them in place.
Example attachment point. This is the feedpoint of the antenna. The two wires to the right are part of the loop antenna, while the wires towards the bottom serve as the balanced feedline. I used some Goop® adhesive on the zip-ties to help hold them in place.

Deployment

For my initial tests, I used a 28-foot Jackite pole to support the antenna. I only partially-extended the pole, such that the bottom of the antenna was about 4 to 5 feet off the ground. I used some nylon twine and a couple of tent stakes to tie off the two bottom corners.

This is the delta loop set up for my intial testing. The light-colored wires were difficult to photograph, so I enhanced them for visibility.
This is the delta loop set up for my intial testing. The light-colored wires were difficult to photograph, so I enhanced them for visibility.

The setup was somewhat more complicated than most portable antennas I use. It took me about 20 minutes to get it set up, but I suppose that wasn’t too bad for my first time. 

I used a couple of large tent stakes to keep the feedline off the ground. I connected the antenna to my KX3 using a 4:1 balun and a 1-foot piece of coax. 

I used a couple of large tent stakes to keep the balanced feedline portion of the antenna off the ground.
I used a couple of large tent stakes to keep the balanced feedline portion of the antenna off the ground.

Results

I first did a quick check to see what bands the KX3’s internal antenna tuner would handle. I found that I could load it up on every band from 60M through 6M, although I couldn’t get the SWR below 2:1 in the low end of 40M. That’s not surprising for a 20M loop, I suppose. I did have a usuable match between 7.030 and 7.060, where I normally operate.

I was only about 50 yards away from some powerlines, but the loop seemed quiet on receive. 

On 20M, a French station answered my third CQ. I also made contacts with Missouri and wrapped up with yet another French station. 

From the signal report the last station gave me, this antenna appears to do reasonably well with DX on 20M running QRP. It was a chilly and windy day, so I didn’t stay out there to try for contacts on other bands. 

Wrap-Up

Although my initial outing with this antenna was promising, I need to spend some more time using it on bands other than 20M. In any event, it was a fun—and cheap—antenna project.

73, Craig WB3GCK

References:

[1] DeMaw, D. (1991). Technical Bits & Pieces. In W1FB’s QRP Notebook (2nd Edition, pp. 157–161). Newington, CT: QST.
[2] DeMaw, D., & Aurick, L. (1984, October). The Full-Wave Delta Loop at Low Height. QST, 24–26.

4 thoughts on “Speaker Wire Delta Loop”

  1. Interesting, Craig. I’ve got a fair amount of speaker wire I’ve accumulates in 40′ to 100′ coils. I’ve only used it for random wires and was happy with those results. I’ll have to try a Delta Loop when spring arrives -which should be soon! Thanks! Mike, KE0GZT

    Liked by 1 person

  2. You can make a loop that’s a full wave on 20 m (and thus a half wave on 40 m) match easily if you open it up halfway around the loop from the feed point. Then you’ve got a half-wave doublet bent into a crazy triangle.
    One way to avoid having to lower the thing when you want to switch between 40 m and 20 or 10 m is to open it up halfway around and then connect a run of twin lead or other balanced line across the insulator at that point. This added stub should be 1/4 wave long on 40 m (taking velocity of propagation into account and the far end of it should be shorted. So on 40 m it presents an open circuit across the insulator, just what you want. On 20 m it’s 1/2 wave long and with its far end shorted, it presents a short circuit across the insulator, just what you want. On 10 m it presents a short at the insulator too, again just what you want.
    What about 15 m? The delta loop is 3/2 waves long on 15 m if it is a full wave on 20 m so you want the far end at that insulator open. And that’s just what the stub does on that band too.
    The WARC bands will however present probems unless you have a good tuner.
    David VE7EZM and AF7BZ

    Liked by 1 person

    1. Interesting thoughts, David. I like the idea of opening it up halfway around the loop. I might have to give that a try. 73, Craig WB3GCK

      Like

  3. Craig :
    I was going to suggest the same thing the David did, which is to replace the splice with a small insulator and a jumper to bridge it. When it is open it up you have a bent 40m dipole. This is how the DK9SQ loop is designed, except that it is configured as a diamond, rather than a triangle. It should solve your 40m matching problem.
    I hope that you and your family are doing well in these strange times.
    Cheers
    Michael VE3WMB (PB#19)
    P.S. I ended up on your blog as I was looking for posting on the 1:1 UNUN that you use on your rain gutter antenna.
    I think I am going to try using my rain gutters as an antenna and see if I can get a match on 160m.

    Liked by 1 person

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