Shure PA421A Antenna Combiners are complementary accessories for Shure PSM Personal Monitor systems. When multiple systems are required for monitoring environments, the PA421A combiners quietly and efficiently optimize RF management for up to four PSM transmitters when racked in a central location, while also reducing rack clutter. PA421A combiners ship with UA802 Coaxial Cable. PA421A combiners replace PA421SWB Antenna Combiners.