Playing with a magnetic loop antenna
Pre-history
The last time I played with a loop or magnetic antenna it was in the late 1980s… Everything was different then. I didn’t even know that a network analyzer or antenna analyzer existed. Well, now it is easier 🙂
- It is possible to make the antenna from basic materials and reach the expected decent performance
- It is possible to tune it rather quickly and easily if you have an antenna analyzer
- As expected, the biggest problem is that it is a very narrow-band antenna. You need to adjust the tuning capacitor all the time if you don’t work on the same frequency
- It is directional & little gain … i.e., you have more cons than pros
- It didn’t work in my apartment conditions – inside the apartment in front of a large window – because the external city/building noise was still too high. But when I am in the field, I don’t see much value in the loop antenna because I have plenty of space, and the performance of the vertical 1/4-waves is much higher
I planned to use a copper tube as it shall be. However, it turned out that basic shops in Kazakhstan don’t sell or use copper tubes anymore as water pipes – only plastic, aluminum, or plastic+aluminum composites. Buying a 50-meter roll wasn’t in my plans. Thus, I had to play with aluminum of 20mm external diameter (including plastic). The aluminum diameter was 15-16mm or so.
The key to everything is the antenna analyzer. If you have it – enjoy any kinds of antennas. If you don’t have it, get it. Just get it.
Will I ever use loop antennas?
It is always nice to play with with something new, but only if I have other options, I won’t use them because:
- Not the best performance by far, particularly for DXing. Vertical 1/4-waves are simple, inexpensive, still a good size, and nearly perfect for simple antennas
- Very narrow bandwidth. The higher the efficiency – the lower the bandwidth. Annoying
- Making automatic adjustment pulls from playing with antenna to playing with microcontrollers. I have more of that in robotics. I don’t need more with antennas
- Higher efficiency requires higher cost materials for the loop antennas, for example, vacuum capacitors … what is the point in such antennas if you can build a far better vertical 1/4-wave for a fraction of the cost of the capacitor alone