The SM-30 is an unidirectional, electret microphone designed for base station operation with an Icom transceiver

Microphone type: Unidirectional electret condenser mic (preamp built in)
Impedance: 600 ohms
Sensitivity: -28 db +/- 4db
Power requirements: 8VDC (supplied from transceiver)
Cable length: 3' 3"
Weight: 12.3 ounces