Claudio wrote.....

P.S.: shorting turns to adjust the inductance of a coil should
      not be harmful,

When I was bringing up the Decca here last winter and trying to get power
into the antenna I found that shorting turns had a disasterous effect on the
performance of the loading coil.  I learned quickly to leave the unused coil
OPEN at the top, for those with Telco experience, a "bridge tap".  When I
quit shorting turns I found the antenna current went up and the radiated
signal also went up.

Just my experience....

Larry
VA3LK