that transmitter must send a audio through it, for a distance of 20meters and the receiver takes and send via speakers ......... how to do it .......... (we need to transmit a audio from a transmitter for about 20meters) ....... plz tell me the specification also ... frequency range ... wht type of modulation required ...........plz .........

Use a wireless microphone. What concerns do you have about the frequency range and type of modulation?

Some cordless telephones have the intercom feature, good enough inteligibility for voice use.

You do not have to care about frequency (it is already FCC approved) nor modulation type, will be likely FM.

Retired cordless units are a cheap source of such approach.

 

If a louder output is needed like for public addressing, a domestic stereo + speaker can serve the purpose. The audio feed from the remote handset (or base) 20 metres away can be taken tapping from its internal speaker (or earphone connector) trough a jack to feed the amplifier input.

 

If the application is for high fidelity music, come back with details of your audio source, and frequency response desired.