Something was wrong with my antenna. I could not achieve the QSOs I was used to. I called people, but they did not answer. Listening was normal, but transmitting suffered. What was wrong?
My HF-antenna is a horizontal wire loop. I measured the resistance of the loop. It was 1.2 ohm as usual. Then my suspicion turned to the ATU which was sitting outdoors under the roof. Could corrosion have harmed the relays? Was there a bad component on the balun PCB?
I took the ATU down and measured the attenuation from input to output using 20 W RF.
- 3.5-14 MHz close to 0 dB
- 18 MHz about 0.5 dB
- 21-28 MHz about 0.7 dB
The balun was the next object to investigate. I discovered that a screw had become loose. It was the screw securing the wire from the balun output to the antenna terminal. The antenna was thus galvanically disconnected from the balun because this particular screw had gone loose! Here was the explanation of the mysterious lack of contacts! Although galvanically disconnected, there was still a small capacitance between the balun terminal and the antenne wire. I estimated this capacitance to be 1 pF or less.
|No connection between balun and antenna.|
- RA0AUC, 20m, my signal -22 dB, JT9
- LU8HGI, 15 m, my signal -20 dB, JT65
- RN6HGN, 15 m, -25 dB, JT9
Regards from OZ1BXM Lars Petersen