An interesting titbit of knowledge about direct conversion transmitters is the phenomenon of injection locking. If the transmitter is such that right after the modulation the signal goes to the driver/PA ( i.e there is no up-conversion or filtering of any kind between the PA and the modulator and its associated LO, then feedback from the output can cause ( in a number of cases) the LO frequency to shift and lock to another harmonic of a feedback signal. A number of techniques to alleviate this have been investigated because the direct conversion technique is considered by some to be simple and easy to handle ( keep chip size small). For more information or articles visit our website at http://www.signalpro.biz.