The 38T cancels noise best when held very close to the mouth, and it discriminates against all sounds more than ½-inch away. A position at one side of the mouth is best to minimize popping, hissing and breathing sounds when speaking.
Microphone Gain Adjustment
The gain is adjustable through an opening in the side of the microphone housing using a small, flat-blade screwdriver. Clockwise rotation of the control increases gain. Adjustment by a qualified avionics technician is recommended, as excessive gain can cause transmitter overload distortion.
FAA TSO Approval
The 38T microphone is certified for aviation use under FAA TSO C58.