I obtained my A license in June of this year, and I'm a beginner. Because my location is quite far from the local repeater, using a handheld radio to connect would require me to go up to the roof every time, and the results wouldn't be very stable. This led me to consider setting up a U/V glass fiber antenna + small vehicle platform. So I purchased an inexpensive 1.2m glass fiber antenna from Taobao, assuming it would be installed on the rooftop of my building.
Just a few days after setting it up, although other stations were still experiencing some noise, I was able to connect reliably to the repeater. About a month later, one of my contacts reported that they couldn't hear me properly; initially, I suspected overheating, but I decided to test my antenna using a vector network analyzer. The results showed that my antenna had become severely over-tuned, with VSWR exceeding 50:1.
So, I decided to try and repair the antenna myself. After taking it apart, I found that the internal structure was very simple, with a capacitor connected between the oscillator and the feed point. My initial suspicion was that the capacitor had failed, creating an open circuit. Therefore, I purchased several inexpensive ceramic capacitors from Taobao (around a few yuan each) with a capacitance of 5pF, as described above.
After replacing the capacitor, I soldered the new capacitor in the same location as the old one (at the bottom with the coil), and then tested the impedance. The impedance was now within acceptable limits, but the center frequency was slightly off. I suspected that there might be a small difference in the soldering position, which didn't significantly affect performance.
At the antenna feed point and the location of the added inductor coil, you can see blue ceramic capacitors:
Standing wave after replacing the capacitor:
So, I eagerly re-installed the antenna and tried to connect to the repeater again, but I was able to connect successfully.😍However, this wasn't a one-time occurrence. Within a few days, the same problem reappeared, and the antenna failed again during testing. I first tried replacing the capacitor, which unsurprisingly fixed the issue temporarily. After reinstalling the antenna, however, the capacitor failed again shortly after. In total, over two months, I had to replace three capacitors, but fortunately, they were quite inexpensive.
Of course, I can't replace the antenna and capacitor every two days; that would be too much trouble. However, with my current budget, replacing the entire unit is the most straightforward option.🤔"Since all the problems seem to be related to capacitors, I suspect that the issue is with the quality of the capacitors themselves. So, I bought some imported TDK capacitors and tried them out. However, after three months, they haven't failed again."🤩"If UU has encountered a similar problem and doesn't want to replace the antenna, they can try replacing the capacitor themselves. Be sure to use a better-quality capacitor to avoid having to keep changing it."
Cheap domestic capacitors:
Some good ceramic capacitors:
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