My DIY magnetic loop with a homebrew air variable capacitor | SWR 1.2 at 7MHz
我制作的带自制空气可变电容的小环天线 | 7MHz驻波比1.2
This is the magnetic loop antenna I built, and the tuning capacitor is completely homemade.
这是我制作的小环天线，其中的调谐电容是完全自制的。
I just finished my first magnetic loop build, and I made the variable capacitor myself instead of buying a commercial one. I'm really excited to share the details with everyone here.
我刚完成了我的第一台小环天线制作，没有购买成品电容，而是自己动手做了这个可变电容。非常高兴能在这里和大家分享制作细节。
Here are
the full specifications of my project:
以下是这个项目的完整参数：
- Homebrew air variable capacitor: Fabricated from 0.5mm thick aluminum sheets, with a 3mm clear gap between the stationary plates. The side support plates are made of 4mm thick fiberglass (FR4) board. Maximum capacitance reaches approximately 170pF.
- 自制空气可变电容：采用0.5mm厚铝片制作，静片之间的净空间距为3mm。两侧支撑板使用4mm厚玻璃钢板（FR4）。最大容量约为170pF。
- Feedline: 3.1 meters long 50-9 coaxial cable (50Ω impedance, 9mm outer diameter, electrical performance equivalent to RG-213).
- 馈线：3.1米长的50-9同轴电缆（50Ω阻抗，9mm外径，电气性能相当于RG-213）。
- Main radiator loop: 8mm diameter copper tubing.
- 主辐射环：8mm直径铜管。
- Coupling loop: 247mm in diameter.
- 耦合环：直径247mm。
- Support rod: 25mm diameter PVC plastic pipe.
- 支撑杆：直径25mm的PVC塑料管。
Initial testing results are very satisfying. I can tune the SWR down to around 1.2 at 7MHz (40m band), which is way better than I expected for a first homemade build.
初步测试结果非常令人满意。在7MHz（40米波段），我可以将驻波比调谐到1.2左右，对于第一次自制的天线来说，这个表现远超我的预期。
I would really appreciate any tips on improving the antenna's bandwidth or optimizing its performance on higher frequency bands. Feel free to share your thoughts and suggestions!
如果大家有关于提升天线带宽或者优化更高频段性能的建议，我会非常感激。欢迎分享你的想法和意见！
