Shure PA421B Antenna CombinerThe PA821B active broadband antenna combiner streamlines the simultaneous operation of many PSM systems at a venue. The PA821B combines the RF outputs from up to four PSM transmitters into one RF output to feed a single transmit antenna. This provides significantly improved reception quality due to reduced intermodulation distortion and dropouts due to multipath interference. (Directly replaces PA421A.) The PA421B is compatible with Shure PSM300, PSM