Some consideration

[Mike(Mont)]

The longcoil of wire can be replaced with the earth and the receiver coil is simply the target's excited magnetic field. The transmitter coil does not need to be a coil, but a coil is more powerful but directional. Notice the line he says the receiver coil needs the correct resistor or the signal will be reflected. So something there to look at.

[omar]

I think Mike raised a very important point about signal reversal.
As far as I know, the impedance of the receiving coil determines the detection bandwidth. For example, the more resistant the coil is, the more sensitive it is to low frequencies, and vice versa with high frequencies. The second most important point is grounding the receiving coil antenna to the ground, which prevents reflection of the ground signal, reduces noise, and improves reception. Let us not forget that what we are studying is a ground signal that moves from an area of high pressure to an area of low pressure on the Earth?s surface. Therefore, I think the detection circuit must have a third common ground with the ground signal. Until it is received and analyzed.
Mike, tell me what your theory of the phenomenon is.

[Mike(Mont)]

I was trying to say that I am still sick enough I don't want to spend much brain energy right now.