Seems to me that would have to be the effect of waves being reflected off the ground back to the antenna element (akin to the effect of a parasitic element).
Originally Posted by G3TXQ
73, Cecil, www.w5dxp.com
Random length "tuned feeders" usually de-tune
an antenna system (thus requiring a tuner).
Yes, that was the only change. No, I did not.
Originally Posted by W5DXP
The antenna is the one you see here below... Very spartan!
Anyhow, I've just made the point of the situation and I think I'll try a couple of things but I'm feeling very lazy to do anything but going to the seaside.
I'll let you know how I'll cope with it as soon as I have something done.
Furthermore, the antenna is supposed to be pulled down within 3-4 weeks (when I'll leave this summertime QTH for the main QTH) and will be put up again next year.
Many thanks to all for your precious and interesting help.
For anybody interested in some numbers, instead all of this albeit interesting discussion
loosely based on experience, here is a link.