Source coding is much about removing the redundant data or the data which is not that important for the data to be conveyed to the receiver, I mean the extra data. It is more like quantizing and run length coding. where in you can send a code like '05'(zero five)which symbolizes five zeros at a stretch instead of sending 00000. So in source coding we remove more of a redundant data which is not
Channel coding :Channel coding is more about adding some extra bits in the form of parity bits so that you can protect the data from being becoming corrupt. Or these data will also serve as the mathematical encryption. And also even helps in correction the corrupt data.
Modulation: Modulation is more about choosing appropriate signaling scheme and translating the baseband signaling to the high frequency and also involves choosing and using the effective modulation schemes perfect for the channel scenario.