A signal booster was a vital component of any communications system and was designed to strengthen the signal.
When Lieutenant Uhura was picking up a faint distress call from an unidentified spacecraft, while the USS Enterprise was in orbit of Capella IV, Mr. Scott suggested she "put a booster on it" and "try to pull it in." (TOS: "Friday's Child")
While crash landed on an unnamed planet in the Gamma Quadrant, Quark told Odo that the signal booster of the USS Rio Grande was completely shot. (DS9: "The Ascent")