The A500RA21 is a UHF flexible whip antenna with Right-Angle BNC for IFBT4 Block 21. The R400A is a high performance, triple-conversion, frequency synthesized UHF receiver fully compatible with all Lectrosonics 400 Series Digital Hybrid Wireless transmitters, 200 Series and 100 Series analog transmitters and Lectrosonics IFB transmitters, plus some analog transmitters from other manufacturers.