please explain metal/mineral on a BFO

[giuhalftrack]

I know the basic BFO working principles but I never understand why some old units have a mineral side on the tuning knob.

I understand that the tuning knob will shift frequency of the reference oscillator to be near at the frequency of the search oscillator.

If we pass the...

[pelanj]

I need to search a relatively small piece of land to find small silver and copper coins amongst larger pieces of iron (nails, screws, horseshoes). The easy ones have been picked up already by others. I think there are some more, not necessarily deep. Nobody likes to dig iron, me neither. Someone mentioned...

[mikebg]

Best circuit for search oscillator (quiz)

Here are different circuits of LC oscillators, where L components are used as sensor for metal: Colpitts, Hartley, Meissner, Armstrong etc. When L is close to metal target, the frequency of oscillation is shifted. This principle of operation is...