I forgot to mention the circuit also acts as a pick up as a radio or tape player when brought close to the sense coil the coil and circuit pickup the voices from the speakers of any tape player and may also do the same for a telephone also when i brought my handy cam close to it it sensed the em fields generated by it to the sense head setting has been constructed onto a bread board and tested with a already made vlf receiver with audio amp now the vlf receiver section that will allow the signals from the sense head section to pass through, and very low frequency signals will pass through still but are filtered some more with the 0.1uf ceramics then it will still sense ac mains at a lower response with the flux concentrator core removed than it would with the core left through the coil so if your outside the electromagnetic environment leave the core in for maximum sensitivity, good idea noty to wear any battery operated watch as mine gets sensed so easily with my other 2 vlf receiver circuits and your ears will get a pounding from the loud ticks as the em pulses from your watch are greatly amplified through the whole circuit and the em signals from your watch are very low frequency signals so these signals will pass through the vlf receiver circuit to unimpeded, and the last circuit is the audio amp section so you can plug head phones in to listen, also the vlf receiver circuit takes a 9 volts battery and its input voltage is linked to the front sense head section so they can both share one 9 volts battery the second nine volts battery powers the audio amp section and its good this way, cause if you switch off the vlf receiver section the audio amp section appears to still be using some, of the circuit when power is removed from the vlf receiver section and you will still get some signals coming through it some how and ive got these same results with the first 2 other upgraded modified vlf receiver circuits and it can still sense em pulses from a ticking watch to but at a lower response to, the flux concentrator is made up of a number of barrel shaped toroid slipped over a stick or a pole shaped core and inserted through the coil, the circuit also sounds like a comic receiver for weird signals to with the core taken out so it dose what i think a vlf receiver dose then. Not very good at the technical explanation well ill give it a go the sensing signal booster on the far left hand side i bread boarded that to test it, to see if i can get more signal boost with it and the coil with its inductive nature pending on the amount of winds of thin wire and also the flux concentrator, this concentrate the em flux when a signal is induced into the coil and it increases sensitivity more, if you was to take it out the sensitivity and strength of signal would drop but then your in another mode as the circuit would still act as a lightening detector sensing lightening and the crackles will indicate that and the ac environment well it would sense that but at a lower response to it unless you re insert the flux concentrator core then the hum from ac mains will be increased a lot.

Vlf receiver circuit