how to get the message from modulated wave?

[electronics_kumar]

there are numerous number of waves floating in the atmosphere....if it is reception by means of synchronous method, it is easy to demodulate by fixing the local oscilltor to generate same carrier as that of transmiter carrier(by making tuning circuit persent in the receiver to resonate at carrier frequency)
In non-sync. demodulation, how we are able to pickup particular wave floating in the atmosphere wihout using a local osc.

 

[rednewguy]

the problem in demodulation is that the carrier generated at the receiver may not have the same phase as that of the received due to some difference in phase caused in the medium. in non-synchronous demodulation we extract the carrier from the received signal itself( from antenna take two parallel wires, one passes thru a squaring ckt, filter and then a frequency divider. here we get carrier in phase with that of the recieved). then deploy a multiplier to demodulate.