Canon fax basic 2000 서비스 매뉴얼

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G3 FACSIMILE COMMUNICATIONS

5.3

Modulation Methods up to 9600 bps

Here, let’s describe modulation methods having a data transmission speed

up to 9600 bps that is currently used on almost all facsimiles.

5.3.1 Frequency shift keying

Frequency Shift Keying (FSK) is a modulation method that is widely used

on facsimiles to transmit facsimile procedure signals. By FSK, the fre-

quency of the carrier wave is changed to express digital data.

Fig. 5-38 shows an example of FSK. In this example, digital “0’s” is

expressed by a signal of 1850 Hz and digital “1’s” is expressed by a signal

of 1650 Hz. The length of frequency components that shows each numeri-

cal value is 1/300 seconds. In other words, 300 frequency components are

transmitted in one second.

As each component is equivalent to a single bit, the data transmission

speed using FSK becomes 300 bps.

This type of FSK system is recognized by

dations are called ITU-T recommendation V.21.

Fig. 5-38 Frequency Shift Keying

Transmission speed 300 bps

Digital signal

(facsimile procedure)

Time

Amplitude

Analog signal

(FSK modulated wave)

1/300sec.

1850Hz

1650Hz