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Building a Gawant-style antenna has been a lot of fun. Now that I have a general understanding of its characteristics, here's a summary. Due to the messy wiring, I decided to disassemble and reassemble it. In doing so, I also measured the SWR values of various baluns. The specific method involved using a 51Ω resistor in place of the antenna and measuring with a SARK100 antenna analyzer.
First, a forced balancing barrel was made using an FT50-43 magnetic ring. It had 11 turns and used 0.5mm enamel-coated wire.
The image shows the raw wiring state of a Baron aircraft that has not yet been fully assembled.
Great! The performance in the HF band is excellent. The 50 MHz band is also mostly usable. However, there are discontinuous jumps in SWR near 40 MHz and 49 MHz. After multiple retests, the trend remains consistent, which may be a characteristic (or problem) of the SARK100?
Next, a floating balun was constructed using an FT83-43 magnetic core, with 17 turns and 0.5mm coated wire.
Huh? The wires crossed somewhere in the process… I only noticed this when I enlarged the photo.
Indeed, it's quite bad... It seems that using a parallel routing method (also known as "star topology") does indeed lead to higher transmission line impedance.
Therefore, it was decided to use a bidirectional and interleaving method, maintaining 17 turns in the winding while still using 0.5mm insulated wire.
Although it's much better than before, the performance is still not ideal.
Next, the test used a similar FT82-43 magnetic ring, but with a version made using ultra-fine Tongzhou cable winding. The number of turns remained at 17.
The cables were very messy and difficult to manage; perhaps they should be secured with zip ties.
The performance is significantly better than the coaxial cable version, and it's clear that coaxial cables are superior! However, the SWR (Standing Wave Ratio) is still close to 1.5, which means it's slightly under optimal. Therefore, it's recommended to use frequencies below 14 MHz. If higher frequencies are required, consider reducing the number of turns.
Although I really wanted to use this coaxial cable version of the floating balun for Gawant's clone antenna, unfortunately, its size was too large to fit inside the enclosure.
Initially, I created a version with 13 turns, using an FT240-43 magnetic ring and RG-58A/U coaxial cable. The 13 turns were chosen because a 1-meter length of the coaxial cable was just enough. (Photo omitted).
That's incredible! The SWR (Standing Wave Ratio) remained stable at 1.0.
I also tried winding a 15-turn version using an FT240-43 ferrite ring and a 1.5m RG-58A/U coaxial cable. This was the maximum number of turns that could be accommodated on the ferrite ring without overlapping. I left 20cm of extra length at each end.
This version of SWR also perfectly matches 1.0 and performs excellently.
Practical experience has shown that the floating barrel (common-mode chokes) design, using a large-sized magnetic core and a thick-diameter coaxial cable, achieves better results.
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