ELT, CVR and DFDR are three completly different things.
Emergency Location Transmitter is a part of aircraft emergency equipment and transmits a signal on three emergency frequencies (by operating a switch in a cockpit or upon a crash G-switch closes and ELT operates automatically). 121.5 Mhz (which is normally picked up by the closest ATSU/SAR), 243 MHz also picked up by SAR, 406 MHz picked up by satellite. They have a built-in test program also which enables the pilot/engineer to test it for proper operation without triggering SAR
CVR and FDR (DFDR) are recorders and that's exactlly what they do. Record data. They do not transmit anything. They are, however, equiped with ULB (underwater location beacon). It's a small metal cylinder that transmits an ultrasound "ping" (only) when submerged into water. The ULB is only used to locate the CVR/FDR if the aircraft crashed into the water, as they can get displaced quite far from the original crash site due to currents...