On 1/14/21, the VSWR on the A3S went bad as shwn on the plots below. The resonant frequencies for 40 and 20 meters moved to above the bands. 15 meter resonance was below the band. Only 10 meters was about right.
|Since there had been a failure of a trap before, the traps were suspect. Pulling the cap off the end of the traps away from the boom (the shell of the trap is connected to the side towards the boom, so high voltage is developed on the end away from the boom), no sign of melted insulators like before was visible. To avoid having to take the whole antenna apart, a continuity check was done on each trap in place. It was found that trap TC on one side of the driven element was open. The photo at right shows what was found when the trap was opened. The sheet metal screw connecting the high voltage end of the coil to the tube was not screwed in.|
|Next it was found that the hole the sheet metal screw that connects the shell of the trap to the boom side element tube was stripped so the screw could not be tightened. A solution for that was to insert a short piece of 3/4 inch wood dowel in the tube so the sheet metal screw could screw into the wood. This resulted in a good tight connection between the tube and the trap shell.|
I generally try to repair the A3S without removing it from the mast (which is a REAL PAIN!). I can loosent the boom to mast U-bolts so the boom can rotate. I can get the ends of the elements down to roof level where the traps can eaisly be reached. The boom is then rotated the other way to reach the other side of the elements. Here, however, when the problem was not immediately evident, I did pull the antenna off the mast, quickly found (loose screw in trap causing lack of continuity through the trap) and fixed the problem. If I had thought of doing the continuity test when the antenna was still on the mast, I could have saved a lot of trouble and waiting for the wind to die down. Next time, I'll try to remember to do trap continuity tests!
Below are VSWR sweeps after the trap was repaired.