BUILDING A 49:1 TRANSFORMER AND CRAFTING A 10-40M EFHW ANTENNA: MY PERSONAL JOURNEY.

By Marius Lubbe ZS1ML

Hello to all my fellow radio enthusiasts! I recently embarked on an exciting adventure in the world of ham radio. My mission? To construct a 49:1 transformer and then add wire to create a 10-40m End-Fed Half-Wave (EFHW) antenna. Let me share my experience with you!

1. My Introduction to the 49:1 Transformer

At the heart of my EFHW antenna project was the transformer. I learned that this component is crucial for matching the high impedance of the antenna to the 50-ohm impedance of our radio equipment. The 49:1 transformer was the perfect fit, transforming the roughly 2450 ohms of a half-wave antenna down to a neat 50 ohms.

Materials I Gathered:

• A toroid core (I used the FAIR-RITE FT240-43)
• Enamelled copper wire (I opted for around 1mm in diameter or 18 AWG)
• A sturdy enclosure
• Connectors (I went with the SO-239)

2. My Experience Winding the Transformer

Step 1: I started by winding three bifilar turns of the enamelled copper wire onto the toroid core. Winding two wires together at the same time was a new experience for me, but it was essential for the primary winding.

Step 2: Next, I wound 14 turns of the same wire around the toroid for the secondary winding. I made sure the windings were tight and evenly spaced.

Step 3: I then connected one end of the primary winding to one end of the secondary winding. This became my ground connection.

Step 4: The other end of the primary winding I connected to the centre pin of the SO-239 connector, and the free end of the secondary winding was ready for the antenna.

Step 5: To protect my transformer from the elements, I housed it inside a suitable waterproof plastic enclosure.

3. Adding the Wire for the 10-40m EFHW Antenna

With the transformer ready, I was eager to add the wire for the EFHW antenna.

Step 1: I measured out a wire length of approximately 20.35 metres (or about 66.8 feet) to cover the 10-40m bands.

Step 2: I attached one end of the wire to the free end of the secondary winding from the transformer.

Step 3: I tried to elevate the wire as high as possible, keeping it in a straight line. At the other end I anchored to a non-conductive support.

Step 4: I connected the ground of the transformer to a suitable earth. I also added a counterpoise of about 5 metres (16.4 feet) for good measure. This is optional as some operators will argue that the EFHW works as well with or without the counterpoise.

4. My Testing and Tuning Process

With the antenna in place, I was keen to test and fine-tune it.

Step 1: I used an antenna analyser (Nano VNA) to check the SWR (Standing Wave Ratio) on my desired bands.

Step 2: The SWR was a bit high on one band, so I trimmed the wire slightly. I found it helpful to start with a longer wire and adjust as needed.

Step 3: Once I was happy with the SWR readings, I made sure to secure all connections and waterproof any exposed areas.

Conclusion

Building my 49:1 transformer and setting up a 10-40m EFHW antenna was a truly rewarding experience. Every time I make a distant contact using this antenna, I’m reminded of the magic of ham radio and the satisfaction of a DIY project. If you’re thinking of diving into antenna building, I say go for it! Happy transmitting from my shack to yours!