In the meanwhile I found the shielded antenna detector so it has to be directional:
THE FERRITE TREASURE SENSOR
http://www.geotech1.com/forums/showthread.php?t=14935
And i will test with open basis transistor, microvoltmeter, opamp circuits in series and all kind of stuff that can signalize the smallest amounts of EMfield, frequency or current-changes. Not to forget all kind of different antennas, coils...
btw. ferrite is blocking / absorbing HF! Anyway: Let's start the action.
edit: look what I've found - I could try this self created "Super Amplifier"-schematic with 2 PNP transistors from 12 years ago: