In the world of amateur radio, building your own antenna can be one of the most rewarding projects. If you’re looking to enhance your VHF transceiver’s performance on the 144 MHz band, building a Yagi antenna is a fantastic choice. Known for its high gain and directional capabilities, a Yagi antenna can significantly improve your signal strength and reception quality.

Materials Required

1. Boom: Typically made from aluminium or wood, the boom serves as the backbone of the antenna.
2. Elements: These are also generally aluminium rods or tubes. You’ll need several elements of differing lengths.
3. Element Mounting: Insulating materials like plastic or nylon spacers to mount the elements onto the boom.
4. Coaxial Cable: For connecting the antenna to your transceiver.
5. Balun (optional): To ensure balanced/unbalanced signal transition.
6. Tools: Drill, screws, measuring tape, saw, and a soldering iron.

Design Specifications

A standard Yagi antenna comprises a driven element, a reflector, and multiple directors. For a Yagi tuned to 144 MHz, the lengths and spacing between these elements are critical.

1. Driven Element: This is the part of the antenna that connects directly to your feeder. For 144 MHz, the length should be approximately 1 meter (approximately 39.37 inches).
2. Reflector: Positioned behind the driven element, the reflector is about 5% longer than the driven element. Thus, for 144 MHz, it would be around 1.05 meters (41.34 inches).
3. Directors: Placed in front of the driven element, directors are shorter, typically about 95-98% of the driven element’s length. Therefore, they would measure around 0.95-0.98 meters (37.4-38.58 inches).

Steps to Build Your Yagi

1. Assemble the Boom:
– Cut the boom to the desired length, which will depend on the number of directors you plan to use. For a basic 3-element Yagi, a boom length of about 1.5 meters (59 inches) should suffice.
– Mark the positions where each element will be mounted. For optimal performance, the reflector should be spaced about 0.2 wavelengths (approximately 14 inches) behind the driven element, and the directors should be spaced about 0.15 wavelengths (approximately 11 inches) in front.

2. Prepare the Elements:
– Cut the aluminum rods to their designated lengths.
– Ensure the ends are smooth and free of burrs to avoid any interference or damage to cables.

3. Mount the Elements:
– Secure the elements to the boom using insulating spacers. The driven element needs to be insulated from the boom, whereas the reflector and directors do not.

4. Connect the Coaxial Cable:
– Attach one end of the coaxial cable to the driven element. It’s recommended to use a balun to connect the coax to the antenna for balanced signal transfer.
– Solder the connections to ensure they are secure and free of interference.

5. Tune and Test:
– Connect the other end of your coaxial cable to your VHF transceiver.
– Test the antenna by transmitting and receiving signals. Fine-tune by adjusting the positions of the elements if necessary.

Tips for Optimal Performance

– Height: The antenna should be mounted as high as possible, ideally at least 10 feet above ground level.
– Orientation: Yagi antennas are directional, so ensure it’s pointed towards the area you wish to communicate with.
– Weatherproofing: If you’re mounting the antenna outdoors, consider weatherproofing the coaxial connections and other joints.

By following this guide, you’ll be well on your way to building a high-performance Yagi antenna for 144 MHz VHF communications.

Happy building, and may your signals always be clear and strong! James, G1JOB!