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:
Good C code to study is the Virtual Wire:http://www.airspayce.com/mikem/arduino/VirtualWire.pdf
These 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.