I dont really know how to put my doubt in words but I will try. Electromagnetis waves of various frequencies are used for communication.Also there are EM waves from other sources, for example even sunlight is eloctromagnetic wave.Now all these waves are out there in space. So at any one point in space, it will be kind of a resultant of all EM waves at that point. [Like may be if you mix water from various sources ] So what I think is if it were possible to see the electromagntic field at any point, we would end up seeing one resultant value. Now how does receiving antenna seperate the wave it wants? I was syudying science at one time, but forgot, so please clear my doubt.And bear with me if my question doesnt make sense.