The internal current limiters of the generators are limiting factors up to 50kHz.
From there on the inductance of the coil is the limiting factor and the current flow quickly decreases.
It is usable at 75k but at 100k is barely measurable.
We receive consistent signal strength of up to 50k. Above that, the signal strength varies.
This is why I set the limits to 50k.
For more details, please check the link: