Hi Valerio and all,
my marconi has abt 1%% = -30 dBi efficiency. And yes, i think you are right 
when  you guess that our short monoples have the same. The hope is, to get 
more. But who is able to tell us how to achieve? Experiments with 1.8 MHz are 
lowbandactivities concerning shortwaves but it is far away from 137 kHz. Well, 
we all know how hard it is to decrease the groundloss but is there anyone who 
will do the work for an EH-antenna? Most of you  are asssuming a big 
construction by reasonable theoretical thinking but as far as i know nobody 
made the job. So may be the EH-antenna will be a never ending dream :-))