I visited this site some time ago, but it might be very useful for background information about the frequency range that our Blitzortung systems operate in. It covers Natural Radio, Whistlers, VLF reception, LF reception, antennas and the need for low-noise reception areas.
The site "Radio Waves Below 22KHz" is a treasure trove of information.
There is info regarding loop antennas, ionosphere waveguides, you name it.
It is run by Renato Romero, who has written a book on Natural Radio.
Here is the link:
http://www.vlf.it/Enjoy.
Greg H.
