Basically a circular inductor with a ferrite core instead of air which allows it to be more compact, have a higher inductance per volume and a greater q factor

Basically a circular inductor with a ferrite core instead of air which allows it to be more compact, have a higher inductance per volume and a greater q factor (bandwidth). A different inductance (different number of wire turns) is needed depending upon several factors, especially if you are using them to make a resonant circuit (a circuit that responds to a particular frequency). It does not generate the signal. I hope I got that right.