| 释义 |
ground start modems using double sideband modulation (DSB). Group I machines conforming to international standards use Frequency Modulation (FM), transmitting at two frequencies, with 1500 Hz pegged as the white frequency and 2300 Hz as the black frequency.The North American standards peg 1500 Hz as white and either 2300 Hz or 2400 Hz as black. As Group I machines used no compression mechanism, transmission was slow at about 4–6 minutes per page, even at the relatively poor resolution of about 100 scan lines per inch (lpi). Group I machines used an obsolete electrochemical printing process and are, themselves, considered obsolete. See also compression, DSB, facsimile, FM, and resolution. |