It is well known that Nyquist filters are used often in digital communications. A popular filter is the root raised cosine filter used both at the transmitting end and at the receiver. Together these two filters generate the raised cosine response which is what is needed. The obvious question that has to be asked is, why use these filters at all?  The answer is that we use these filters because: (1) They slow down fast edges in the input signal so less bandwidth is required. Slower edges use less bandwidth. The filter smooths the edges of the signals. (2) At the receiver end the reduced bandwidth improves the sensitivity because more noise and interference is rejected. Please visit http://www.signalpro.biz for more information.