Shure A15RF In-Line 3-Pin XLR Radio Frequency AttenuatorThe Shure A15RF reduces interference from AM radio stations that may bleed into microphone lines when using long cables in microphone installations such as suspending choir microphones. The A15RF passes phantom power, and can be used with condenser microphones. For best results, the A15RF should be installed at the end of the cable nearest to the microphone. In situations where this is not practical, the A15RF can also be installed at the mixer input,