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Creating a dual band vertical antenna can be a straightforward and budget-friendly project, perfect for anyone looking to enhance their ham radio setup. In this guide, we'll walk through the construction of a vertical antenna that operates on both the 20m and 17m bands, using simple materials and techniques that can be executed in your own backyard.
Why a Vertical Antenna?
Vertical antennas are often celebrated for their compactness and effectiveness, especially in limited spaces. A well-constructed vertical can offer significant performance improvements, particularly when elevated above the ground. This guide focuses on building a vertical antenna that not only fits into small gardens but also maximizes signal strength.
Basic Principles of Vertical Antennas
A vertical antenna consists of a radiating element and at least one ground radial. The performance of a vertical antenna improves significantly when it is raised above the ground. For our project, we will construct a vertical antenna for the 20m band, which will also facilitate operation on the 17m band through a clever addition.
Materials You Will Need
Before diving into the construction, gather the following materials:
- 5m of wire for the vertical radiator
- 5m of wire for the first radial
- Shorter wire for the second radial (approximately 1.8m)
- Coaxial cable (KX cable) for feeding the antenna
- Fiberglass pole to support the vertical element (non-conductive)
Designing the Antenna
The design of our dual band vertical antenna is quite simple. The vertical element will be a quarter wave long for the 20m band, which is approximately 5m. This vertical will be mounted about 2m above the ground to optimize its performance. The first radial, also 5m long, will extend outward at an angle of about 30 to 40 degrees from the base of the vertical.
Adding a Second Band
The key to making this antenna work on both the 20m and 17m bands is the addition of a shorter radial. This second radial will allow the antenna to resonate on the 17m band, which requires a slightly different configuration. By ensuring that the total length of the vertical and this additional radial equals a half wavelength on 17m, we can achieve resonance on both bands.
Construction Steps
Now that we have the design and materials ready, let's go through the construction process step by step.
Step 1: Setting Up the Vertical Element
The first step is to set up the vertical element. Securely attach the 5m wire to the top of the fiberglass pole. Ensure that the pole is stable and can withstand outdoor conditions. Elevating the vertical to about 2m above ground is crucial for improved performance.
Step 2: Installing the First Radial
Next, attach the first radial wire (5m) to the base of the vertical. This radial should extend outwards at an angle. Make sure it is securely connected and that the wire is not touching the ground.
Step 3: Adding the Second Radial
Now, take the shorter wire (approximately 1.8m) for the second radial. This radial will need to be trimmed for optimal performance on the 17m band. Attach this wire to the base of the vertical as well, ensuring it is positioned correctly for resonance.
Step 4: Feeding the Antenna
Once the vertical and radials are in place, it's time to connect the coaxial cable. This cable will feed the antenna and is essential for transmitting and receiving signals. Connect the cable at the feed point of the vertical antenna.
Tuning the Antenna
After construction, the next step is tuning the antenna to ensure optimal performance on both bands. Start by testing the 20m band. You should aim for a low SWR (Standing Wave Ratio), ideally around 1.2:1. For the 17m band, you may see a slightly higher SWR, potentially around 2:1, which is still acceptable.
Fine-tuning the Radials
To achieve the best performance on the 17m band, you may need to trim the second radial slightly. Use an antenna analyzer or a SWR meter to monitor the changes as you adjust the wire length. This process will help you find the resonant point for the 17m band, allowing for efficient operation.
Performance Benefits
The elevated vertical with radials set at the correct angles can significantly enhance your signal strength. With this dual band vertical antenna, you can expect improvements in both directivity and gain. The configuration allows for effective communication over long distances, making it a valuable addition to your ham radio setup.
Comparative Advantages
Compared to traditional ground-mounted verticals, this design offers superior performance due to the elevation and the use of radials. The combination of a quarter wave radiator and strategically placed radials can provide as much as 6 dB gain over a standard ground-mounted vertical. This improvement translates to clearer signals and better range.
Maintenance and Adjustments
Maintaining your antenna is straightforward. Since the radials are above ground, they are easy to access for adjustments. After heavy weather or if you notice performance changes, check the connections and the integrity of the wire. Regularly inspect the pole and connections to ensure everything remains secure.
Conclusion
Building a dual band vertical antenna is not only a rewarding project but also an excellent way to enhance your ham radio operations. With minimal materials and effort, you can create an effective antenna that performs well on both the 20m and 17m bands. Enjoy your newfound capabilities and happy communicating!
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