harmonic illiminator

Hi every body;
I am having problem on designing a filter circuit which can pass only the fundamental frequency what so ever signal is given.
let me clarify my ques.
I want to design a filter (single filter) which is capable of passing the fundamental frequency when signal of differnt frequency with harmonics comes into its input terminals.

Is there any way to use automatic tuned notch filter.If yes please give me idea.
thank you.

SWH,
A phase-locked-loop will lock onto the incoming frequency. Its square-wave output can be filtered with a switched-capacitor-filter IC, whose clock is derived from a counter/divider that is referenced to the PPL.
The filtered output will be just the fundamental frequency without harmonics.
The input signal should be a steady amplitude, perhaps requiring an automatic gain control.
Hey, this won't work if the PPL locks onto a harmonic frequency.
Is this a guitar tuner project?