80/20m loaded coil dipole antenna update

Here is an update on the progress with 80/20m loaded coil dipole antenna. Brought down the antenna and measured both sides in order to correct any inequality which had occurred after multiple trimming efforts. Trimmed a further 10cm on either side of the elements before the coil, meant for 20m. Though the antenna was still resonating fairly well on 30m, no pick of CW signals was obtained on reverse beacon network. Resonance pattern on 30m band had shifted a bit upwards. Length before the coils was around 4.3m after trimming. Lower part of 20m band tunes with the built-in tuner of FT-710, though SWR seems to be above 5 without tuning.

As the antenna wire was 2.5 sq mm, it would have a diameter of 0.07 inches. The online calculator which I had been using showed that an inductance of 129.2 microhenries would be needed. I had measured the inductances of the coils which I had made as 119.8 μH and 122.1 μH respectively. Increased the total antenna length to 39.55 feet, with the distance to the center of the coil kept at 14.12 feet. Revised calculation showed that an inductance of 124.9 microhenries are needed for resonance at 3.6 MHz. Added 3 inches of antenna length to both sides by unfolding the folded back part of elements beyond the loading coils, to make total antenna length 40.05 feet.

Revised calculation showed 120 microhenries are needed for each coil. Repeat testing after mounting the antenna showed SWR 1.25 at upper end of 30m band and 1.5 at lower end of it. SWR was more than 5 on 20m band and going up on higher part of the band. Still auto-tuning would work at the lower end of the band. HI SWR was noted on 80m band through out. Looks like I am stuck without resonance on 80m and high SWR on 80m. As a next step I am planning to check the inductance of the coils once again in the mounted situation and decide on further options.