Thông tin thiết kế mạch P12

TELECOMMUNICATION TRANSMISSION MEDIA In this chapter the characteristics of the media in which the transmission of signals takes place will be discussed. It so happens that we humans basically communicate through speech=hearing and by sight. Human hearing is from 20 Hz to 20 kHz and we can see only the portion of radiation spectrum from about 4:3 Â 1014 Hz (infrared; l ¼ 7 Â 10À7 m) to approximately 7:5 Â 1014 Hz (ultraviolet; l ¼ 4 Â 10À7 m). These communication channels occupy only small portions of the detectable frequency spectrum which has no lower boundary but has an upper...