Canon fax basic 2000 서비스 매뉴얼

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G3 FACSIMILE COMMUNICATIONS

5. MODULATION METHOD

After the document is scanned, the resulting image data is converted to

compressed digital data by coding described in the previous section. How-

ever, the telephone line that is used when transmitting that digital data is

for transmitting analog signals “voice,” and the digital data cannot be

transmit as it is. To transmit this data actually using the telephone line, the

digital data must be converted to analog data. Conversion from digital sig-

nals to analog signals is performed by the facsimile’s MODEM. Here, let’s

describe the various modulation systems that differ according to the

MODEM in use.

5.1

Modulation and Demodulation

On a facsimile, the digitally coded image data varies the analog carrier

wave. Converting digital signals to analog signals in this way is called

“modulation.” When modulation processing is performed, the digital

information is moved onto the changes in the carrier wave. Changing the

carrier wave in this way is called modulation by digital signals. There are

various modulation method: method that are amplitude-dependent, fre-

quency-dependent and phase-dependent, for example.

Let’s describe modulation using digital signals using a simple example to

aid understanding. Fig. 5-37 shows an example of Amplitude Shift Keying

(ASK) method.

Fig. 5-37 Example of Amplitude Shift Keying Modulation

Digital signal

Time

Amplitude

(H)

(L)

”1”

”0”