Question

What is MODEM? Draw it's block diagram and explain it's working.

Answer 1

MODEM: The modem in the FAX machine at the receiving end converts the analogue signal back into digital pulses. The printer of the FAX machine prints these digital pulses in the form of dots to build up a facsimile copy of the original document.
Working: In order to send FAX copy of some documents, the sender dials in the phone number of the FAX machine at the receiver's end. The FAX machine at the sender's end is then in transmitting mode and that at receiver's and in receiving mode. When a FAX machine is in receiving mode, only its printer is active so as to accept the incoming signal through the modem inside ot.
The original written document is now put in the machine. The optical scanner scans the whole document in form of tiny parallel strips. When an intense beam of light from a source falls on the scanned document, the amount of light that becomes back is detected by sensors. These sensors are called charge coupled device which converts the light packets into electrical signals. Where ink is present, little light is reflected creating an electrical pulse of low voltage. A pulse of high voltage results, when light is reflected from white paper. A modem inside the machine converts these digital pulses into analogue signals which is then transmitted to the receiving FAX machine through the telephone line.