[roberts]

Listen, some things are not to be generalized, the way usually laics do. And i ment mostly on Esteban's way. Now, this time i am serious, i do not mean to provoke Esteban with this or to say he is ignorant. This time i am very serious and like to point on usuall Esteban's generalization and simplification of some things, he probably saw or heared somewhere or loearned on wrong way.
Ok Esteban, you also, if you want to be constructive than do not feel offended with this, you simply can not generalize all the things here.
If you saw somewhere in some radio an RF choke with ferrite core screwable and it was used to fine redjust some frequency - this doesnt mean EVERY possible ferrite core have same function. No, not at all. RF chokes with ferrite screw inside usually do have simillar function, mostly to adjust small coil to be resonant on some incoming/outgoing signal. Best example would be TOKO type cores for AM/FM etc.etc. Yes in these cases man can usually adjust some frequency with those.
But using plain ferrite rod as sort of antenna with resonant coil wounded over it is quite another case. Moving core more in/out of windings doesnt automatically mean you gonna readjust some frequency. Mostly it means adjusting level of induction - amplitude of induced current.
So i would rather say; if that gap makes any sence than its role should be to adjust amplitude of induced (in this case received) signal from nearby coil. Is it nearby? I really dont know? I havent seen orientations yet. But logically i am presuming ferrite rod must be in some logical conjuction with other coils?
Otherwise i really do not understand rod's role at all here?
So let;s say i guessed right; operater can adjust amplitude by dealing with gap. Ok.