Hi Giulio, I think you are right that a lot of the amateur stations with big
signals often have a substantial amount of horizontal wire. However I dont
think the big night-time signal is due to horizontal polarization or
radiation from the horizontal wire.

The night-time signals over a path distance of 1500 to 2000kms are often 20
to 30 dB higher than the signal levels in daytime (see the average line on
my propagation plots). This is probably due to a higher 'reflection'  level
and less absorption at night. The higher night-time level is even evident
with commercial stations whose radiators are predominantly vertical. The
other more important effect of horizontal wire is demonstrated in some of
the measurements that I described on my web site, and is the consequent
reduction of ground loss that extensive horizontal wire gives. Few amateurs
can afford to install the kind of ground systems that are used by commercial
stations, so this reduction of loss by increasing the top-load is valuable.
I have some further meaurements from Finbar EI0CF that I have not had time
to include yet on the site. These detail additions to the top-load of his
main vertical, and the resultant reduction in loss, measured with an RF
bridge.

Reino has been heard in the UK in daytime and occasionally with the distinct
signs of fading, so his signal is received by ionspheric 'reflection' even
in daytime.

Cheers de Alan G3NYK
[email protected]
http://www.alan.melia.btinternet.co.uk