1.KTH17B mine explosion proof telephone 2.have emergency calling function 3.frequency 300-3400HZ,65db Specifications1.KTH17B mine explosion proof telephone 2.have emergency calling function 3.frequency 300-3400HZ,65db 4.MA , EXSI CERT.1. The safe type of KTH17Btype mine nature automation telephone set is that the standard produces according to Q/HX001-2007 it’s outer covering is selected and used ...