SMDV FlashWave-III RX2 Radio Slave Receiver for Speedbox Diffusers - Receiver Unit Tiny radio slave receiver for SMDV Speedbox Diffusers Works with SMDV speedlight mounting bracket model SB-02 and SB-03 Replaces the cold shoe on the speedlight mounting bracket to trigger speedlights Max sync speed of 1/250s. 2.4 GHz operating frequency. 16 Channels! Requires SMDV FlashWave-III transmitter unit (sold separately)