Shure PA421B Antenna Combiner

The PA421B is a passive 4-to-1 RF combiner designed to consolidate the antenna outputs of up to four PSM-series IEM transmitters into a single broadband antenna. Instead of running four antennas off four transmitters and turning your stage wings into a forest of paddles, you feed each transmitter's RF output into one of the four BNC inputs and drive a single antenna from the combined output. That single antenna still covers all four transmitter channels simultaneously. For anyone running a multi-pack PSM system, this is how a tidy, professional deployment actually happens.

Passive design is the headline spec that matters most here. The PA421B draws zero watts — nothing to power, nothing to configure, nothing to fail mid-show in the way an active component could. The tradeoff is insertion loss: combining four RF signals passively means each transmitter sees some loss before the signal reaches the antenna, so you'll want to verify your link budget still has enough headroom for your venue size. At 1U and 200mm deep, it sits cleanly in a standard IEM rack without reaching back into the bay. At 1.4 kg it's light enough that it won't stress a shelf mount, though you should still rack it properly.

If you're running two, three, or four PSM300 or PSM900 packs and want a clean antenna solution without a powered distro, this is a direct, reliable answer. It's also the right call when your system tech wants to minimize active components in the RF chain. Where it's not the right fit: if you need to feed a remote active antenna distro like a Shure AD4D setup, or if you're combining antennas on the receive side for wireless mics rather than transmitters — this is transmitter-side only. Larger touring systems with more than four packs will need multiple units or a different architecture entirely.