Speaker Wire Half-Square Antenna

I’ve been intrigued by the half-square antenna for some time now. I don’t have the real estate to put one up at home, so I built one for portable use. Like my other speaker wire projects, this antenna is built from a 50-foot length of cheap, two-conductor wire.

You can think of the half-square as two quarter-wave verticals spaced a half-wavelength apart. It provides some gain over a quarter-wave vertical and has a low take-off angle. The half-square has a bi-directional pattern with lobes broadside to the antenna and nulls off of the ends.

Normally, the half-square is fed with coax at the top of one of the vertical elements and functions as a single-band antenna. The coax should be kept perpendicular to the vertical leg, to avoid interaction. That arrangement, however, would be somewhat awkward for a portable antenna.

For expediency in the field, I went in a different direction. I decided to feed it at the bottom of one of the vertical legs, which is a high impedance point. I use a 9:1 unun to reduce the high input impedance to something easier for a tuner to handle.

I designed this antenna for the 20M band, but I wanted to use it on other bands as well. By using the 9:1 unun to feed the bottom of the antenna, I’m able to squeeze some more bands out of it. A tuner is required, of course.

Speaker Wire End-Fed Half-Square Antenna
Speaker Wire End-Fed Half-Square Antenna

Materials

Here’s what I used to build it:

Construction

Refer to the accompanying diagram to help make sense of the following steps.

  • Separate the speaker wire into two 50-ft wires
  • On one of the wires, install a spade lug at one end. This will be the connection to your matching device)
  • From the spade lug, measure up 16′ 7.2″ and make a small loop using two small zip-ties. 
  • From the second wire, cut a length that is about 16′ 9″ or so. 
  • Strip and splice the smaller wire to the end of the larger wire. After soldering it, I covered the splice with heat-shrink tubing. 
  • Next to the splice, make another small loop, using two zip-ties.
  • At the end of that wire, twist the wire to form an attachment loop. When you do this, make sure you have 16′ 7.2″ from the splice to the attachment loop.
  • I applied some Goop® adhesive to the loop at the end of the wire to hold it together. I also added Goop® to each of the other attachment loops.
  • As is my usual practice, I added some Goop® to where the wire enters the spade lug to add some strain relief.
  • At this point, the antenna is finished. You can, however, cut the leftover wire in half to make two radials for 20M (approximately 16 feet, give or take). I installed a spade lug on each of these wires and twisted the other ends to make a small loop. You guessed it; I put Goop® on these wires, as well.
This photo shows the splice and one of the mounting loops used in the Speaker Wire Half-Square.
This photo shows the splice and one of the mounting loops used in the Speaker Wire Half-Square.

Matching

[Update (6/17/2020) – After initially publishing this post, I received some great feedback from readers. As a result, I have updated, clarified, and expanded this section.]

For my first couple of outings with this antenna, I used a 9:1 unun as a quick and dirty way to get it on the air. I run about 18 feet of RG-8x coax from the unun to the radio. There’s nothing particularly critical about the coax length, but I would recommend a minimum of 16-feet for 40M and up. The exact length of the radials isn’t critical either since they’re laying on the ground. In fact, you can probably use the antenna without them. In this case, you’re relying on the coax shield for the counterpoise.

While the 9:1 worked fine, there are more efficient ways to match this antenna. I plan to continue experimenting with other methods to match the high-impedance input on 40M and 20M.

I haven’t tested them myself, but the end-fed halfwave tuners from Pacific Antenna and QRPGuys should work on 20M and 40M. They use a parallel resonant circuit and are designed to match an end-fed halfwave (EFHW) antenna. 

An EFHW transformer, like the ubiquitous 49:1 transformer, should also work. You will likely need to do some pruning on the antenna to get the SWR where you want it.

Finally, a simple L-Match antenna tuner with a tapped inductor in series and a variable capacitor across the output looks like it may be the best solution for me. It should handle the high impedances on 40M and 20M, and work on other bands like a random wire tuner. This will definitely be part of my next round of experiments.

Deployment

Deploying this antenna is a snap and takes me about 5 minutes. I use two collapsible poles to support it. I attach one corner to a partially-extended 28-foot Jackite pole. The feed point of the antenna is about 3 feet off the ground. 

These are the two poles I used to support the Speaker Wire Half-Square. Unfortunately, the wire is too thin to be visible in this picture.
These are the two poles I used to support the Speaker Wire Half-Square. Unfortunately, the wire is too thin to be visible in this picture.

I use a 20-foot Black Widow pole (actual length about 19.5 feet) to support the other end. I support this pole with an appropriately-sized screwdriver shoved in the ground. The handle of the screwdriver fits snugly inside the bottom section of the pole. After attaching the other corner of the antenna to top of this pole, I extend the pole and remove the bottom cap. Next, I walk the pole back until the horizontal section is taut. Then, I just shove the screwdriver in the ground and place the pole over it.

With appropriate trees nearby, you might be able to eliminate one or both of the poles. I’m not usually that lucky.

Results of Field Testing

I was pleased with the results of my initial field tests with the half-square. The internal tuner in my Elecraft KX3 was able to load the antenna from 80M through 6M. (Since the antenna’s input impedance is low on 80M, I wouldn’t recommend using the 9:1 there.) The SWR was 1.2:1 or better on all bands with the tuner. 

During my first outing with the half-square, I was able to make contacts on 40M, 20M, and 15M at 5 watts with no difficulty. The antenna is a half-wavelength on 40M, and it appears to play well on that band. I had numerous Reverse Beacon Network spots on 40M showing a signal-to-noise of 20db or better.

I also used it in the field during a recent QRP contest with similar results. Signals were strong on 40M, and I worked Georgia and Quebec on 20M.

This was hardly a rigorous scientific evaluation, but I’m happy with this antenna so far. One of these days, I’d like to do some modeling to see what the radiation patterns look like on the various bands. In the meantime, I’ll do some more experimenting with impedance matching.

Wrap-Up

This was an easy and fun project. It certainly made good use of a roll of cheap speaker wire. After using this antenna in the field a couple times, I have officially added it to my arsenal of portable antenna options.

73, Craig WB3GCK

My Activities of Late

I haven’t been posting much here lately. The COVID-19 pandemic and other family obligations have been cutting into my ham radio activities. Nevertheless, I do have a few projects in the works.

A few weeks ago, I started another project in my ongoing series of speaker wire antennas. This one will be a variant of the bi-square antenna. This antenna has the potential to be a little more field-friendly than the delta loop I tested last month. It’s all built; I just need to get out somewhere to set it up and see how it works.

I’ll file my next project under the category of Old Dogs/New Tricks. Back in December, I bought a Kenwood TH-D74a HT. That gave me the ability to reach a nearby D-Star repeater. This week, I purchased an MMDVM hotspot to go along with it. I plan to spend some time in the coming days getting it set up. I’m hoping to be able to eventually connect to the DMR talk groups used by my ARRL section and local ARES-RACES groups. Fortunately, my local group has some experienced hotspot users I can consult if I run into any snags. Wish me luck.

Sadly, our camping season with our little QRP Camper is off to a late start. State park campgrounds in our area have been closed due to pandemic. We have reservations at a state park in Maryland next month, however, and it looks that might be our first trip of the year. I’m looking forward to a little QRP-portable operating from the camper.

My local QRP club has started making plans for Field Day. We have a set of social-distancing guidelines we’ll be following this year. We’ll be limiting the number of participants, keeping our tents at least 10 feet apart, and eliminating common eating areas. Also, we won’t be sharing stations and equipment. This year’s Field Day will be different, for sure. 

Other than that, I’ve been active on our local ARES-RACES nets, and I have been checking into the Pennsylvania NBEMS Net on Sunday mornings. 

You can also find me on 40M or 80M CW in the evening. I usually hang out around the SKCC watering holes.

I’ll be posting more on all of this stuff in the coming weeks. Until then, stay safe, and I’ll see you on the air. 

73, Craig WB3GCK

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.

Dollar Store Special

[NOTE: This is an updated version of an old article from my QSL.NET website. In the interest of full disclosure: My local dollar store no longer sells the speaker wire I used. While it’ll probably cost you a few more bucks to build one, it’ll still be a cheap antenna. Although the original article has been on my website for 15 years, I still get the occasional email from folks who have built one.]

I love rummaging through our local dollar store. One of the biggest bargains in our local dollar store is speaker wire. You can get 50 feet of two-conductor speaker wire for a buck. Not too shabby. I always keep a bunch of the stuff on hand for antenna experimentation. 

Diagram of the Dollar Store Special. See the text for other counterpoise options.
Diagram of the Dollar Store Special. See the text for other counterpoise/radial options.

Using a single 50-foot roll of dollar store speaker wire, I made a simple 50-foot random wire antenna with counterpoise wires to cover the 40, 30 and 20-meter bands. I stashed the whole kit in a zip-lock sandwich bag and always keep it on hand as a backup antenna system whenever I operate in the field. With a simple antenna tuner of some sort, this will get you on the air in a pinch, should your primary antenna fail. 

This is the 20 AWG speaker wire I used. Sadly, my local dollar store no longer carries it. I wish I had bought a ton of it while it was available.
This is the 20 AWG speaker wire I used. Sadly, my local dollar store no longer carries it. I wish I had stocked up while it was available.

Here’s all you have to do:

  1. Separate the conductors so that you now have two separate 50-foot wires.
  2. For the radiator, take one of the 50-foot wires and crimp a small ring lug to one end—right over the insulation. This gives you someplace to tie a line to hoist it up. On the other end, just strip off a half-inch or so of the insulation. You can leave it bare or add whatever kind of connector you want; whatever works best with your tuner.
  3. For the counterpoise wires, take the remaining 50-foot wire and cut it so that you have a 33-foot wire and a 17-foot wire. If you only want to work 40 and 20 meters, you can stop right here. You now have counterpoise wires for both of these bands.
  4. To provide a counterpoise wire for 30 meters, take the 33-foot wire from Step #3 and cut it so that you now have a 23-foot wire and a 10-foot wire. Strip off about 1/2-inch of insulation from one end of the 23-foot wire. Install a quick-disconnect connector of some sort on the other end, so that you can join the 23-foot and 10-foot wire sections together. The idea here is that, with the two wires connected, you have a 33-foot counterpoise wire for 40 meters. With the two sections separated, you now have a 23-foot counterpoise wire for 30 meters.
I used a ring terminal to terminate the 50-foot wire. Note that the terminal is crimped over the wire's insulation. The metal ring terminal is electrically-isolated from the antenna wire.
I used a ring terminal to terminate the 50-foot wire. Note that the terminal is crimped over the wire’s insulation. The metal ring terminal is electrically-isolated from the antenna wire.
This is the quick-disconnect connector I used on the original version of the counterpoise wire.
This is the quick-disconnect connector I used on the original version of the counterpoise wire. I used some Goop® adhesive to provide some strain relief.

[Note: If you only plan to operate with the radials laying on the ground, cutting them to resonance isn’t too important. You can simplify things a bit by going with just the 33 and 16-foot wires. I think two 25-foot wires would be sufficient, as well. Three 16.6-ft radials is another option to consider. Feel free to experiment here and see what works for you.]

In operation, just hoist one end of the 50-foot radiator up in a tree or other suitable support. Connect the other end to the hot side of your tuner. Connect the 33-foot and 17-foot counterpoise wires to the ground connection on your tuner and lay them out on the ground. When you want to work 30 meters, just disconnect the quick-disconnect on the longer counterpoise wire. Pretty simple, eh? Any type of simple L-tuner should work fine for this. 

Please note that I wouldn’t recommend using this wire for a permanent outdoor antenna. It’s not suited for that kind of use. But for temporary outdoor use, it’ll do just fine. Besides, if the wire goes bad, you can always replace the whole thing for a dollar! 

73, Craig WB3GCK

©2005-2020 Craig LaBarge WB3GCK