Maximize Your QRP Setup with This Ultra-Portable End-Fed Antenna

By KE2YK

If you’re a QRP operator looking to maximize your signal while minimizing your gear, building a portable end-fed antenna could be your perfect solution. In this guide, I will attempt to walk you through how to build a portable QRP antenna for hiking and camping—designed specifically for QRP radio operation with easy-to-follow steps

What Is QRP, and Why Does It Matter?

QRP refers to operating a radio with very low power, typically 5 watts or less. In the world of ham radio, the goal is often to make contacts over long distances with minimal power—sometimes even just a few milliwatts!
It's a challenge that requires not just good equipment, but the right antenna. That’s where this end-fed antenna design comes in. It’s compact, efficient, and perfect for those of us who love portable setups.

Why End-Fed Antennas Are Perfect for QRP

End-fed antennas are a breeze to set up. Just toss one end over a branch or tie it to a pole, and you’re good to go. For portable operations, that kind of simplicity makes them a perfect choice, especially when you're on the move and need something quick.

But it’s not just about convenience—end-fed antennas are highly efficient when tuned right. They’re designed to handle high impedance (about 3200Ω), and with a little help from an impedance matching device called a UNUN transformer, your radio’s 50Ω input is happy. This ensures that your signal is strong and clear, even with only 5 watts of power, which is essential for any QRP operator.

Impedance Matching: Why It’s So Important

When you use an antenna, the impedance needs to match your radio’s input. If it doesn't, you’ll end up with a poor signal and high power loss.
In this antenna design, the 64:1 UNUN transformer is the key. It matches the antenna’s high impedance to the radio’s 50Ω input, ensuring your radio works efficiently with minimal loss.
This transformer plays a crucial role in making the antenna perform well, especially for QRP operators who are working with low power.

Step-by-Step: How to Build The QRP End-Fed Antenna

Building this antenna is easier than you might think, and it doesn’t require fancy or hard-to-find materials. Here's everything you need to know to get started.

Materials You’ll Need for Your Portable QRP Antenna

BNC Connector: This is what connects your antenna to your radio.

FT50-43 Toroid Core: A small magnetic ring used to create the impedance transformer.

Insulated Copper Wire (0.25mm enamel wire): Used to wind the toroid and form the antenna wire.

100pF Capacitor (1000V): Keeps the circuit stable and helps with tuning.

28.5mm PVC Pipe: This is your coil form for the inductor.

Glue or Resin: Protects the components and ensures everything stays secure.

How to Build an End-Fed Antenna for Portable Ham Radio Operation

Wind the Toroid
Start by winding two turns of wire in one direction, and then add seven more in the same direction. Now, cross the wire and wind seven more in the opposite direction. Keep the crossing wire slightly to the side—this will make installing the SMA connector a lot easier later on.

Create the Inductor
Grab the PVC pipe and wrap 50 turns of wire around it to create your inductor. For the best performance, aim for an inductance of around 34µH.

Attach the Antenna Wire
Now, take a 0.95-meter length of wire and attach it to the inductor. Then, connect the other end of the wire to the BNC connector. Finally, add another 2 meters of wire after the connector to complete the antenna.

Finalize the Circuit
Install the 100pF capacitor between the center conductor (the part that carries the signal) and ground. After that, solder all the connections and insulate them with glue or resin to protect everything from the elements.

Tuning Your End-Fed Antenna for Optimal QRP Performance

Once the antenna is built, it’s time to get it tuned and tested to make sure it's ready to go.

1. Check the SWR (Standing Wave Ratio):
SWR tells you how well your antenna is transferring power. A low SWR (ideally under 2:1) means most of your power is radiated effectively. If your SWR is too high, you’ll need to make adjustments to get better efficiency.

2. Tune the Antenna:
Use an antenna analyzer or SWR meter to see how well your antenna works across the frequencies you plan to use. If it’s not resonant on your desired bands, small tweaks like adjusting the wire length can make a big difference.

3. Test in Real-World Conditions:
Once everything is tuned, it’s time to get on the air and see how far your signal travels. Try digital modes like FT8 to test your reach. If you’re curious about how far your signal is going, use tools like PSK Reporter to check where your signal is being received.

Troubleshooting Tips

Even with a solid build, issues can still arise. Here’s how to troubleshoot:

High SWR?
Double-check the wire length and toroid windings. A small tweak can often fix it.

Weak Signal?
Try raising the antenna higher. The more height you can get, the better.

Too Much Noise?
Moving the antenna away from power sources might do the trick. If noise persists, a common-mode choke can help.

Portable and Field-Use Considerations

When you’re ready to take your antenna outdoors, here are a few tips for deploying it in the field:

How to Set Up and Test Your Portable QRP Antenna in the Field

There are different ways you can set up your antenna depending on your space and what you're trying to achieve:

Sloper: This is a great option if you’ve got the height for it and want long-distance (DX) communication.

Inverted-L: If height is an issue, this is a great alternative. It’s easy to deploy and still gives you good performance.

Vertical: Perfect for low-angle radiation, which is ideal for long-distance contacts. If you have room for it, go for it!

Ground Plane or Radials

Adding a few radials to the ground beneath your antenna can boost performance, especially if you’re using a vertical setup. A simple ground plane can make a noticeable difference in signal quality.

Troubleshooting Tips for Efficient QRP Antennas

If you’re getting noise or feedback, don’t panic. Try moving the antenna away from electrical interference like power lines or large metal structures. Also, adding a common-mode choke to the feedline can help reduce noise.

Experimenting with Variations

One of the best parts about building your own antenna is that you can experiment and make it fit your specific needs. Here are a few things you might want to try:

Toroid Core Alternatives:
The FT50-43 toroid is a great fit for this design, but you can also experiment with other cores like the FT82-43. If you do, though, you might need to adjust the number of turns to get the impedance right.

Multi-Band Operation:
Want to use your antenna on multiple bands? Adding an antenna tuner can help, or you can experiment with loading coils to cover different frequencies. Just be aware that multi-band setups can take a little more tuning to get just right.

Using Different Materials:
Don’t worry if you can’t find the exact components listed here—similar parts will work. Just make sure the capacitor has a high voltage rating (1000V) to handle the power safely.

Real-World Performance

Once you've built and tuned your antenna, you’ll likely want to know how it performs in the real world. Based on user feedback and testing, this antenna has proven to be efficient across several bands, with 20m being its sweet spot.
Users have reported solid performance on FT8 and SSB, making it a great option for portable field operations. Whether you're setting up on a mountain or in your backyard, it’ll give you reliable results in a compact package.

Conclusion: Get On the Air!

Building your own end-fed antenna for QRP is a fun, rewarding project that you’ll enjoy every time you make a contact. With just a few simple materials and some careful tuning, you’ll have a portable, efficient antenna that’s ready for your next adventure.
Whether you’re on a mountaintop or just in your backyard, remember that every watt counts—and with the right antenna, you’ll make the most of them!

Glossary of Terms

QRP: Low-power radio operation (usually under 5 watts).
SWR: Standing Wave Ratio, which measures antenna efficiency.
Toroid Core: A small magnetic ring used in the antenna's impedance transformer.
Inductor: A coil of wire that helps adjust the antenna’s frequency.
Capacitor: A component that helps stabilize the antenna’s electrical signal.
Radials: Wires placed on the ground to improve antenna performance.
Common-Mode Choke: A device used to reduce noise and interference.

Resources and Further Reading

QRP Lifestyle YouTube Channel for tips on QRP operation and antenna builds.
Antenna Theory and Design Guide for more in-depth reading on antenna theory.
PSK Reporter to see where your signal is being received globally.

QRP Stuff

Understanding End-Fed Antennas: Why They Work So Well for QRP