baseband & bandpass

Baseband signals are simple low frequency message which need to be modulated on a carrier for transmission over the BANDPASS channel.In CW modulation the digital signals need to be converted to such a form that the channels like Tx lines, telephone lines and other medium can support. So they use techniques like ASK,FSK,PSK to modulate the baseband digital s/g into an analog s/g which can be sent into the Tx lines.