question_answer 8)

Show that if a device is available which can multiply two signals, then it is possible to recover the modulating signal at the receiver station. 

Answer:

Let there be two signals represented by and where is the amplitude, is the angular frequency of a carrier wave at' the receiving end and  is the amplitude,  is the angular velocity of the modulated wave. Multiplying these signals, we get Using cos(A + B) = cos A cos B - sin A sin B s = cos A cos B - i.e. i.e. The separation of the relationship clearly indicates that the modulating signal  can be easily recovered at the receiving station. The device which can be used for this purpose comprises of LC tuned circuits and is called low-pass filter.