This paper describes the design and implementation of an UWB Impulse Radio transmitter. This UWB transmitter produces very short pulses with possibility of time-shifting to be used in cases of Pulse Position Modulation (PPM) The transmitter, which is based on step recovery diode (SRD), can operate at 50Mbps with high repetition rate. Experimental results show that, ultra short pulses with duration of about lnsec and spectrum exceeding 2GHz at -10dB, are produced and transmitted