Did rain wreak havoc on my fan dipole antenna?

As I had posted earlier, I was happy with my fan dipole antenna with added coils for the 20m elements. I was able to work on six bands with SWR tunable in my radio: 40, 30, 20, 15, 10 and 6m. Yesterday evening we had rain and a mild thunderstorm. So I had to switch off the radio and disconnected the power supply as well as the antenna. Today morning when I checked, the radio would not tune on 30m and 20m, which are usually quite active at that time. Went out and inspected the antenna wires. Nothing seemed to be wrong out there. There was not much of a wind yesterday to cause antenna wires to snap. SWR dip on Nano VNA had shifted down to 10 MHz and was 3.231, beyond the tunable range of the radio on 30m amateur radio band.

SWR dip near 20m band was at 13.025 MHz and 2.681. That was much below the 20m amateur radio band and explained the untunable high SWR in 20m band. So rain had caused loss of access to 20m and 30m bands in my antenna, without any obvious physical damage. Fortunately, SWR was reasonable on 40m, 15m, 10m and 6m. Still when I contacted VU2RZA during the pre-Belgaum roundtable, I was asked what had happened as my signal was weak, 5,7 instead of the usual 5,9. Naturally, I was a bit worried and did not know what to do. Anyway as the rain had subsided at night itself, I decided to wait till sun warms the antenna system.

I was quite happy to see the SWR dip return to 14.150 MHz by 2pm in the afternoon. Sun has undone the damage done by rain the previous night. Though my balun is in a water tight enclosure and had not been giving trouble during previous rainy season, new additions to antenna system were not. The loading coils were not enclosed and the folded back segments of the 20m elements could also gather moisture during rain. These could have caused the shift in SWR. When the very hot sun these days had dried the antenna components by afternoon, SWR would have returned to the previous position.

SWR dip near the 30m band also had returned to 10.2 MHz so that 30m amateur radio band which is just below that became perfectly tunable with the auto-tuner in FT-710. That is a new lesson learned.

Good watertight enclosures are needed where there are vulnerable regions in your antenna system, not just at the balun and feedpoint. Collection of water particles would have shifted the resonant frequency downwards, which returned to previous position after drying up. I can expect much more severe changes during the coming rainy season, leave alone the chance of physical damage to a complex antenna system in high winds.