Do you need a counterpoise?

The End-Fed Half-Wave (EFHW) antenna is a popular choice among amateur radio operators, especially those who enjoy portable operations like QRP, POTA, or SOTA. It’s lightweight, easy to set up, and versatile across multiple bands. But how does it work, and what about the common question: “Do I need a counterpoise?”

How the EFHW Works

An EFHW antenna is essentially a half-wavelength of wire fed from one end, rather than the center. This end-fed design makes it simple to deploy—just throw one end over a tree or other support, and you’re ready to go. Unlike center-fed dipoles that require a feed point in the middle of the wire, the EFHW allows for more flexibility in placement and length.

The key to making an EFHW work is the 49:1 transformer. This transformer matches the high impedance of the antenna (around 2,500 ohms) down to something much more manageable for your radio (typically around 50 ohms). With this impedance match, the EFHW can efficiently radiate your signal.

The Question of the Counterpoise

A counterpoise is essentially a "ground plane" for the antenna, providing a return path for current. It can sometimes improve the performance of an antenna by stabilizing the feed point impedance, especially in end-fed designs. The question is, does an EFHW antenna always need a counterpoise?

In most cases, an EFHW can work effectively without a dedicated counterpoise. The coax feed line often acts as a counterpoise of sorts, especially when you're using shorter lengths of wire. However, some operators find that adding a counterpoise can improve the antenna's performance, particularly when operating on lower bands or in certain environments.

No Connector? No Problem

With my smaller version of the EFHW, there’s no dedicated connector for a counterpoise. But that doesn’t mean you’re out of options. If you find that your setup benefits from a counterpoise, you can simply connect a piece of wire to an alligator clip and attach it to the shield of the BNC connector. This provides a quick and easy way to add a counterpoise when needed without modifying the antenna.

The length of the counterpoise wire depends on the band you’re operating on. For example:

• On 20 meters (HF), a quarter wavelength counterpoise would be about 16.5 feet long.

While these lengths provide a good starting point, you may want to experiment with slightly different lengths depending on your environment and operating conditions.

When to Use a Counterpoise

Here are a few situations where adding a counterpoise might be beneficial:

• Low Bands (80m and 40m): If you're operating on lower frequencies, a counterpoise may help stabilize the feed point impedance and improve performance.
• Poor Ground Conditions: If you're setting up in an area with poor ground conductivity (like rocky or dry soil), a counterpoise might help.
• Interference or SWR Issues: If you're noticing a high SWR or unexpected interference, try adding a counterpoise to see if it stabilizes the signal.

Something else to note, if you use a common-mode choke to protect your equipment, place it as close to your radio as possible. This allows the coax from the choke to the transformer to act as the counterpoise. If your run of coax is too short, you may need to add a wire counterpoise as described above.

A little TLC for my EFHWs

As someone who enjoys both the technical and practical sides of amateur radio, building 49:1 transformers for End-Fed Half-Wave (EFHW) antennas is something I take seriously. Each transformer I sell, whether on my Etsy store or at hamfests, is built by hand, with careful attention to detail.

The Build Process

Each transformer starts with a ferrite core, and I hand-wind the magnet wire around it to achieve the right balance for a 49:1 match. This process isn’t rushed. It’s about ensuring that each turn of the wire is tight and even. The goal is to minimize signal loss and ensure smooth operation when the transformer is in use with an EFHW antenna.

After winding, the core is connected to durable components, like BNC connectors. I choose parts that can withstand regular outdoor use, as many hams take their gear into the field for portable operations like POTA or SOTA. Once the assembly is complete, I test each transformer with an SWR meter to make sure it's ready for the bands it’s designed to cover.

Hand-Built with Care

I build my transformers in small batches, ensuring that they work well in real-world settings. The process takes time, but it’s worth it to know that what I’m offering to fellow hams is reliable and effective. From the first winding to the final test, the focus is on quality.

A Practical Approach

I started building these transformers because I wanted something I could rely on in the field, and I figured other hams might feel the same way. When you operate QRP or portable, you need gear that’s lightweight, compact, and dependable. That’s what these transformers are designed to deliver.

Why I build EFHW antennas

When you're running QRP (low-power) radio, every watt matters. The End-Fed Half-Wave (EFHW) antenna has become a popular choice among hams for good reason. Whether you're operating portable, setting up for POTA (Parks on the Air), or working from your backyard, the EFHW antenna offers reliability, portability, and solid performance. I enjoy POTA the most and frequently make the short trip to K-3036 right down the road at Martin Creek State Park. Here’s why I take my own EFHW with me.

1. Efficient with Low Power

In QRP, you need your antenna to make the most of limited power. The EFHW is known for its efficiency, even with low-power rigs. It delivers a strong signal, ensuring you’re heard without needing a lot of power—perfect for making contacts with a small, portable setup.

2. Easy to Set Up and Carry

The EFHW is designed for easy deployment. Whether you’re in the park, on a mountain, or just out in the field, this antenna can be set up quickly. A tree branch, a pole, or even a telescoping rod can get you on the air fast. Its compact design makes it simple to pack and transport. I typically use a telescoping fishing rod and have even deployed it over the water from a fishing pier!

3. Works Across Multiple Bands

The EFHW's ability to cover multiple bands is another standout feature. With the right transformer—like my own End-Fed Half-Wave QRP Transformer Antenna on my Etsy store—you can switch between popular bands like 40, 20, and 10 meters. This versatility allows you to work different frequencies without needing constant adjustments.

4. Perfect for POTA and SOTA

For POTA or SOTA (unfortunately, no mountains anywhere close here!) operators, the EFHW antenna is an excellent choice. It's portable, quick to set up, and performs well without needing a lot of gear. You can spend more time enjoying the activation and less time fussing with equipment.

5. Beginner-Friendly and Reliable for All

You don’t need to be an expert to get started with an EFHW antenna. It’s easy to use, which makes it great for beginners. At the same time, experienced operators appreciate its reliability and performance during portable operations.

DIY battery pack for POTA

I've been playing around with some different sized cells to build some physically smaller battery packs for my QCX-minis. I only use them about an hour or two at a time, so I don't need a massive power source. However, most store-bought (relatively cheap) LiFeP04 batteries start around 6Ah. So I began looking for small cells to build a custom pack or two.

I found some neat little LiFeP04 cells the same size at AA alkaline cells. Since the are 3.2V each but still fit anything that takes a AA, I had to have a talk with the family to make sure no one accidentally used the "purple" batteries! I also bought a universal charger that could charge them. The unit also charges NiMH, Li-Ion and NiCad batteries with the flip of a switch.

I bought a few balancing units and then complexly over engineered a battery pack. It worked, but it not practical. So, I ordered a case with a lid, power switch and power cord and simplified my life. Now I

POTA outing with the DigiBox

With the extended Christmas break, I had an opportunity to head out to Martin Creek Lake State Park (K-3036) for a POTA activation. I used my revamped DigiBox and my homebrew EFHW antenna. The weather was perfect with clear sunny skies and about 63 degrees outside. It was very comfy in the sunshine! 

I found a covered picnic table near the lake and setup my equipment. I extended my 21-foot collapsible fishing pole and used a rod holder stuck in the ground about 40 feet out from the picnic table to hold it, basically creating a sloper antenna.  

Over all, it worked very well! I made just over 36 FT8 contacts in about an hour and a half. I found the bottleneck on on working contacts was my own clumsiness in clicking stations! Typically, my signal reports were about 10db to 15db below the reporting stations, which I felt pretty good about considering I was running about 4w and the bands were FULL of station.