Antennas: Unlocking the Potential of Endfed-Halfwave Antennas for Portable Use

Are you looking for a versatile antenna that is easy to build and perfect for portable use? Look no further than the Endfed-Halfwave (EFHW) antenna. In this article, we will explore the unique properties of EFHW antennas and how they can revolutionize your communications setup.

The Power of the EFHW Antenna

The EFHW antenna is a true gem in the world of antennas. Not only is it easy to construct, requiring only a transformer and wire, but it also offers a host of advantages for portable use. Here are some key benefits of the EFHW antenna:

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• Easy to build: With just a transformer and wire, you can create your own EFHW antenna in no time.
• Easy to elevate: Setting up your antenna at an elevated height is a breeze, ensuring better signal propagation.
• Easy to feed from the end: Feed your antenna from the end, simplifying the setup process.
• Resonant on multiple bands: The EFHW antenna is inherently a multiband antenna, resonant on the fundamental frequency and all its harmonics.

While the EFHW antenna boasts impressive advantages, it does come with a drawback. Approximately 15-25% of the energy is lost in the broadband transformer. Nevertheless, the benefits far outweigh this minor setback.

The Transformer: The Heart of the Antenna

At the core of the EFHW antenna is the broadband transformer, with an impedance transformation ratio of 1:49. To ensure optimal performance, it is advisable to use a transformer wound on -43 material. The transformer’s size determines the maximum power that can be transmitted through the antenna.

To simplify the winding process and enhance your understanding of the theory, check out this informative video. You can also find various PCBs that assist in different aspects of building your EFHW antenna.

The smaller PCBs provide space for mounting the transformer, compensation capacitor, antenna connector, and have holes for attaching the antenna wire and tensioning rope.

The more advanced PCBs offer additional functionality, such as the ability to wind your antenna wire and rope. You can even find 3D-printed covers to weatherproof the transformer and capacitor, creating a compact and transport-ready package.

Choose the Right Antenna Wire

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The choice of antenna wire largely depends on your specific needs. Here are three popular options:

1. Magnet wire: This lightweight and nearly invisible wire is easy to work with but not very durable.
2. Loudspeaker cable: Affordable and commonly available, loudspeaker cable can be used, but it may stretch under load.
3. Antenna wire: Although more expensive, antenna wire offers excellent durability and performance.

For portable antennas, consider using DX-Wire UL, which is lightweight, flexible, and boasts high tensile strength. On the other hand, DX-Wire FL is recommended for stationary antennas due to its superior conductivity and durability.

It’s worth noting that the recommendations come from personal experience and not from any sponsorship or affiliation.

Finding the Right Wire Length

To make your EFHW antenna resonant on your desired frequency, you need to add a wire with a length of half the wavelength to the transformer. However, the required wire length depends on the elevation height.

In practice, the impedance of an EFHW antenna should be infinitely high at the feeding point and endpoint. However, due to capacitive effects caused by the interaction with the ground, the impedance is transformed to around 2450 Ohms at the feeding point. The amount of current flowing through the antenna depends on the elevation above ground, which affects the feeding impedance.

To determine the appropriate wire length, you can use the following rule of thumb:

• λ = c/f (Wavelength = Speed of Light / Frequency)
• Lambda (in meters) = 300 / Frequency in MHz
• Antenna wire length = Half of the calculated lambda

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The table below provides wire lengths that have been found to work well for various elevation heights:

Wire lengths for lower elevation heights, commonly encountered in portable setups.

Additional Considerations

For optimal performance, it is recommended to use at least 0.05 lambda length of coaxial cable to feed the antenna. For example, for the 80m band, using 5m of coaxial cable is advisable. This not only acts as a counterpoise but also reduces common mode currents when lying the feeding line on the ground.

If you are looking for special variants of the EFHW antenna, DJ5RE’s U01 Antenna is an excellent choice. It is a linked EFHW designed for Near Vertical Incidence Skywave (NVIS) use and covers multiple bands by connecting or disconnecting wire lengths.

To help you with your EFHW antenna project, we have compiled a collection of 3D print files that you can use:

• 3D Printable HASP: Scale it according to your needs.
• Center Triangle + Rope Tensioner for 1mm Rope/Thin Wire.
• Center Insulator and Rope Tensioners for 2mm Rope and UL Wire (recommended).
• Transformer Cover for U01 Hasp PCB.
• Transformer Cover for (small) DL2MAN Hasp PCB.
• Various accessories for the poles used in the setup.

If you found this information helpful, I would greatly appreciate a coffee or beer to support my work.

With the EFHW antenna, you can unlock the full potential of portable communications. Its simplicity, versatility, and impressive performance make it a must-have for any radio enthusiast. So why wait? Start building your EFHW antenna today and experience the power of effective communication on the go.

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Danh mục: Anten - Dây cáp