Temporal transmitter
A temporal transmitter was a communications technology used by the Borg to communicate through time.

Such a transmitter was discovered by Starfleet Intelligence in the late-24th century, in the wreckage of a Borg cube in the Beta Quadrant, and was designated salvage component 36698. 

The transmitter was subsequently stolen by Chakotay and Harry Kim, as part of a plot to change history and prevent the destruction of the , which had crashed on a Class L
planet in the Takara sector in 2375 while attempting to use quantum slipstream drive to return to the Alpha Quadrant. By using the temporal transmitter to send a new set of phase corrections to Seven of Nine's interplexing beacon, they hoped to stabilize the slipstream so that Voyager could remain inside and return home, as they had in the . 

This attempt failed, to Kim's tearful horror – but The Doctor, whose program had been recovered from the wreck of Voyager, refused to admit defeat; at his suggestion, Kim sent Seven a second transmission, which caused the slipstream to collapse, safely returning Voyager to normal space before the crash. ()

See also
Temporal communicator

de:Temporaler Transmitter
Borg technology
Communications technology
Time travel technology