VIDEO
In the world of ham radio, antennas are critical for effective communication. One of the most popular designs among operators is the half wave dipole antenna, known for its simplicity and efficiency. Today, we’re going to explore a unique variant of this design: the end fed half wave antenna. This versatile antenna is easy to make and can be adapted for various uses, making it an excellent choice for both small gardens and portable operations.
Understanding the End Fed Half Wave Antenna
At first glance, the end fed half wave antenna may appear to be just another variation of the standard dipole. However, it carries its own set of advantages. The traditional half wave dipole is a balanced antenna that requires a feed point in the center, typically necessitating a 49:1 unun transformer. While these transformers can be purchased or built, they add complexity and cost to the setup.
Instead, we can adapt the T2LT antenna, originally designed as a vertical half wave antenna, to create a horizontal version. The T2LT consists of a length of coax cable and a quarter wave length of single wire. By connecting the wire to the inner conductor of the coax, we create an effective half wave antenna. This coax cable not only serves as part of the antenna but also simplifies the design.
Building the Antenna
To build the end fed half wave antenna, you will need a few basic materials. The primary component is a length of coax cable, which should be a quarter wavelength long for your desired frequency. For instance, if you are targeting the 20m band, you’ll need approximately 10m or 33ft of coax cable. The process is straightforward:
- Measure and cut a quarter wavelength of coax cable.
- Solder a quarter wave length of wire to the inner conductor of the coax.
- Insert a choke at the point where the wire attaches to the coax cable.
- Wind about eight turns of the coax around a ferrite core, such as the FT240-43, to create an effective choke.
Using RG58 coax is recommended for this setup, as it’s suitable for HF operations. After winding the choke, the remaining coax can be run back to your transceiver. This design not only minimizes the amount of feeder hanging down but also allows for a clean and efficient setup.
Installation Tips
When it comes to installation, flexibility is key. If you have limited space, such as in a small garden or apartment, you can simply hang the antenna out of a window. Position the choke near the window to maintain a tidy appearance while feeding the coax indoors. For those with windows that are difficult to feed coax through, consider using a device like the Comet CTC-50M, which allows for coax feed through a closed window.
This antenna can work effectively as a sloper, descending from your window to a nearby tree or fence. The 20m band is particularly suitable for this antenna, as it allows for long-distance communication throughout the day and into the evening during the warmer months.
Adjustments and Tuning
One of the advantages of this antenna is its adjustability. The choke you created can be moved slightly up or down to aid in tuning. Loosening the turns around the ferrite core allows you to either lengthen or shorten the coax length, which can help fine-tune the antenna’s performance.
Additionally, you can adjust the lengths of both the coax and the wire to optimize the impedance at the feed point. For example, if you have a quarter wave of coax measuring 5m and a quarter wave of wire also measuring 5m, you can experiment by shortening the coax to 4m and extending the wire to 6m. This adjustment will effectively raise the feed point impedance, which may lead to a better Voltage Standing Wave Ratio (VSWR).
Creating a Multi-Band Setup
If you want to use this antenna for multiple bands, you can add a socket just above the choke. This allows you to create separate antennas for different bands, which can easily be plugged into your coax feed. For example, you could have a setup for the 15m, 17m, or 12m bands, which makes this antenna particularly useful for portable operations.
By using a socket after the choke, you can quickly switch between different antennas without the need for extensive rewiring. This level of versatility makes the end fed half wave antenna a fantastic option for those looking to enhance their ham radio experience.
Conclusion
The end fed half wave antenna is a perfect weekend project for both novice and experienced ham radio operators. With a relatively low cost and minimal materials required, it offers an efficient solution for those with space constraints or a desire for portability. By following the steps outlined here, you can create a versatile antenna that meets your communication needs.
As always, experimenting with lengths and configurations can yield positive results, so don’t hesitate to adjust and fine-tune your setup. With this antenna, you can enjoy the world of ham radio, making contacts and exploring different bands with ease.
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