Astatic 636L Noise Canceling Microphone IS the nations truckers choice and for a good reason. The industry standard for over 70 years Astatic 636l does the job right. The 636L is a noise canceling dynamic microphone that has been designed for close quarter handheld applications in CB, Amateur Radio and SSBcommunications. The 636L is used in situations where there is high background noise levels, such as semis, dump trucks, tow trucks, commercial vehicles etc.  The 636L has an extremely rugged housing, and a cool polyurethane coated steel grille screen and an ultra dependable low impedance dynamic element.