Q) What is the approximate maximum bandwidth required to transmit a CW signal?
A) 150 Hz
The abreviation, "CW" means, "continuous wave" and was used to differentiate the original spark-gap generated waves from the early days of radio. CW is used to transmit morse code and is a very narrow bandwidth mode and very efficient. As a result, CW is an excellent choice for attempting a contact under conditions where other modes are not making it. For weak signal work, CW seems to punch through like magic.