AKG AB 4000 High-Performance Antenna Signal Amplifier. High-performance antenna booster for inserting into long antenna cables. One AB 4000 can compensate for approx. 17 dB of cable attenuation, allowing RG 213 cable runs to be extended by approx. 75 m (250 feet). Up to two AB 4000 boosters can be used in series for extremely long cable runs.