Eric Dollard commented on the very first accidental telluric experiments he performed, before he’d even heard of Tesla.
He was messing with a single Tesla Extra coil (air-core high Q resonant quarter-wave coil), observing all its interesting properties, and got a call from a friend a town over telling him he was ‘on the air’ even though there was no antenna.
That was when he realized the ground was acting as a transmission point.
but the coil is the antenna ot was it inside a faraday cage
Knowing Eric it was probably indoors but not Faraday shielded.
In my experience, the Extra coil only works almost entirely in the dielectric field, so even at very high power levels it is difficult to pick up anything more than 1/2 mile away.