RF transmiters and receivers only send and receive digital values, 1 and 0, mounted on a radio frecuency with some kind of modulation: Amplitude, frequency or phase.
There's neither manchester nor any other kind of encoding or decoding method involved in this RF process yet. You have to choose one.
Any kind of noise affects RF, so 1 and 0 can be received from the noise, but it's random! If you try to read what 1s and 0s are received, you'll get many of them, even when your transmiter does't transmit. So you must use an encoding/decoding method to recognize the 1s and 0s you receive (and how you send them). Manchester is a method. There are others, for example the one used by Holtek (http://www.holtek.com/pdf/consumer/6p20v170.pdf
Generic RF remote controls use this holtek chip to encode and decode. I made a program to decode holtek encoding method and works fine. It in this forum, you can check (http://arduino.cc/forum/index.php/topic,129201.0.html