Hi pf, please could someone help explain some concepts relating to bandwidth and radio transmission. As I understand it, radio transmission involves modulating a carrier wave with the signal you wish to send. The bandwidth is the range of frequencies that are contained within the signal. I have read that if the range of frequencies is 4.5kHz then you need 4.5kHz either side of the carrier wave giving a total bandwidth of 9kHz. Why do you need 4.5 either side? If the range of frequencies you have is 4.5 then don't you need 2.25kHz either side? Also, how is the signal actually merged with a the carrier. For example, if your voice is converted into an electrical signal using a microphone then how is this electrical signal put onto a carrier wave? Will the signal be used to generate an EM wave of itself which is then merged with the carrier?