How did my 80/20m loaded coil dipole antenna tune to 30m?

I had been trying to tune my 80/20m loaded coil dipole antenna for the past few days. 20m band was workable in last day’s tuning though 80m band was nowhere near it. Had a quick round of tuning today morning before going out for Sunday routines. Pulled out the antenna wires to the terrace and quickly trimmed 10cm from each side and fixed back the loading coils. Went down quickly to check SWR.

To my surprise, both 80m and 20m bands showed high SWR quite beyond the tuning range of my radio and I was puzzled. This was the SWR on lower end of 20m band, showing it very high.

This was the test at 14.100 MHz, again very high.

See that it was very high at the upper end of 20m band as well and I was thoroughly confused on what had happened with an antenna with which I had worked DX yesterday and had only trimmed just 10cm on either side.

For a curiosity, I checked on upper end of 30m band which had SWR of 5 earlier and I was pleasantly surprised to see that SWR was only about 2.

Checked at the lower part of 30m band and it was similar. Though I was still confused, I was happy to have an antenna to work 30m, on which I have had only one CW QSO so far, that too with my end fed half wave dipole antenna for 20m, using the auto tuner in FT-710.

Started brainstorming on what would have caused such unusual behaviour of my 80/20m loaded coil dipole antenna. Initial I thought that it could be because I had removed a patch cable at the radio end of the feedline because it had developed loose contact at the SO 239 end. This patch cable had SO 239 at one end and PL 259 at the other end. It was meant to reduce the wear and tear of the SO 239 on the radio with repeated connections and removals during my antenna experiments. Even during routine operations, I usually remove the antenna from the socket whenever I stop working, to prevent potential lightning hazards to the radio. But I was rather suspicious of why removing such a short patch cable should change the SWR significantly on 20m band.

Anyway I did not have time for further brainstorming as I had to go out. On my return I saw this and the mystery was solved. In my hurry to go out, I had forgotten to tie the antenna ends to the lower supports and the antenna elements were right on the garden plants! That easily explained the high SWR on the previously working 20m band. Immediately I tied the antenna elements on the lower supports and went back to the shack for testing. Learning point: Haste makes waste!

Checked SWR first on 30m and it was around 4, shattering my interim dream of working a lot of stations on 10 MHz band!

SWR on the upper end of 20m band was around 3, which was quite expected.

SWR was almost similar at 14.200 MHz.

SWR was slightly above 2 at 14.010 MHz, within the tunable range of the built-in automatic antenna tuner of my FT-710 radio. These findings suggest that the resonance is still below the lower end of the 20m amateur radio band and I will have to trim the elements before the loading coil once again to make it resonate for 20m band. Once again reiterating the learning point: Whenever odd SWR values are seen, go out and have a visual inspection of the antenna elements.