An alternate eye 3-d projection system has a projector (2) projecting alternate eye left and right images, has alternating eye 3-d glasses (7) alternating between left and right lens transmissiveness, and has a phase delay unit (29) synchronizing the left lens trans­missiveness to left images and right lens transmissive­ness to right images. A timing shutter (17) is driven through a mechanical link to the projector primary mechanism at a frequency proportional to the frequency of the transition between images. A sensor (21) outputs pulses according to the rotational frequency of the timing shutter. The phase delay unit receives the pulses, a multiplier (31) multiplies the frequency of the pulses, a phase lock loop (33) locks on to the frequency and a counter (35) counts the pulses. After a preset delay the counter outputs a pulse. The delay is adjustable. The counter pulse enables a 60 KHz oscillator (43). The oscillations are counted by another counter (41) and passed to a transmitter (6). The 60 KHz oscillations are disabled when the other counter (41) reaches a preset amount. The other counter (41) sets the duty cycle of the transmitter. Each of the components in the unit is duplicated in a back-up section. The back-up section is enabled when the primary phase lock loop is not locked on and the back-up phase locked loop is locked on. (Fig. 5)