Transistorized microphones for vehicular communications

With the emphasis on intelligibility and reliability, the use of carbon microphones in vehicular communications is rapidly diminishing. Instead, magnetic and dynamic microphones with built-in transistor preamplifiers have been gaining considerable favor. For existing equipment, the amplifier draws its power from the carbon microphone circuit so that, in most cases, equipment changes are not required. Among the interesting possibilities in new equipment is a talk-back provision, whereby the microphone also acts as a speaker. Circuit considerations, environmental stability, and performance will be treated.