Hi there!
I'm a newbi at this forum but i'll try do explain myself the best i can.
I don't know if anyone knows a circuit of a direccional microphone...
Its something that can "hears" a conversation (for example) a fez Km's Miles away.
The circuit can have a antena or just simply made with microphones.
Its not that much to do with the circuit. To do this (though i'm not sure why you want to) you should use something like a parabolic dish. There are directional electret capsules around, but the dish is still better. A shotgun mic can work well too, but I don't think its feesable as DIY.
With circuitry, you just need a high gain mic amp, and some filtering should help you.
I don't know if anyone knows a circuit of a direccional microphone...
Its something that can "hears" a conversation (for example) a fez Km's Miles away.
The circuit can have a antena or just simply made with microphones.
What you are describing is a long-range transmitter. You will need an antenna as well as a microphone. Attach the microphone as close to the conversation source as possible.
What you are looking for was published in Elektor magazine in July-August 2002 Issue. Search www.elektor-electronics.co.uk for detailed article on "directional microphone". I don't know if it works for miles though.