Yes, to get reliable communications with those RF modules you must encode/decode the data.
To learn start by googling and read (Wiki has good info) on the following:
OOK/ASK
Manchester encoding
Good C code to study is the Virtual Wire:
http://www.airspayce.com/mikem/arduino/VirtualWire.pdfThese question of how to use these RF modlues has come up on this (and the SparkFun forum) many times. So search these forums for lots of info and discussions.