... Frequency response:300HZ-400HZ6.Maximum transmission distance:3000M1.Thyssen parts,Five party talkback for interphone2.Two means of communication:Duplex ... three types voltage,24V,12V,6V;Be composed of power supply,main engine,car auxiliary engine,car roof andcar platform. ... party talkback,three party talkback,four party talkback or five party talkback.The advantage is wiring simple,free combination, ...