Modulation Methods Up To 9600 Bps - Canon FACSIMILE BASIC 2000 Service Manual

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 ITU-T, and related recommen-
dations are called ITU-T recommendation V.21.
Digital signal
(facsimile procedure)
1/300sec.
Amplitude
Analog signal
(FSK modulated wave)
Fig. 5-38 Frequency Shift Keying
G3 FACSIMILE COMMUNICATIONS
0 0 1 1 0 1 1
1650Hz
0 0 1 1 0 1 1
Transmission speed 300 bps
Time
0
1850Hz
Time
0
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