Taken from datasheet linked by Psi. here is the diagram application for ACTR433, i think my Cheapo Tx is a variation of this, the transistor maybe driving the SAW device (on-off by serial out digital hi-lo), but i meant, the SAW device is the modulator (mixing digital data with carrier signal at 433MHz), that send the modulated "digital data" out of air (through antenna). I'm not an RF expert myself, but just imagining.