Temporal transmitter
From Memory Alpha, the free Star Trek reference
A temporal transmitter was a piece of technology used by the Borg to transmit messages to Borg drones in another time period.
In an alternate future timeline, Starfleet Intelligence obtained a temporal transmitter from the wreckage of a Borg cube in the Beta Quadrant, designated salvage component 36698. Later, in 2390, Chakotay and Harry Kim stole the transmitter and used it to send a transmission to Seven of Nine aboard the USS Voyager in 2375, when the starship was still lost in the Delta Quadrant.
The transmission contained phase corrections for the failing quantum slipstream drive which Voyager and the Delta Flyer were using in an attempt to return to the Alpha Quadrant. Although the first set of corrections failed to save Voyager from destruction, a second transmission proved more successful, creating a timeline which allowed Voyager and its crew to survive the slipstream experiment and continue their voyage home. (VOY: "Timeless")
