The variable talkback located on the back of the mic.
Magnum 257 echo power microphone for Magnum 257 and 257HP radios.
The new M257 mic from RF limited also has adjustable echo.
No battries needed.
The Magnum Xtreme 257 echo mic is powered by your radios internal voltage via the mic jack.
No addtional wiring is required.
The M257 mic is for Magnum 257 radios only.