sor. The independent elements are discharged by for operation on the public telephone and public data networks, radiated light from the original which is focused on to them. After a which are summarised in Table 60.2. suitable time (1ms) the elements are recharged sequentially. By monitoring the current for this recharge the video signal amplitude is obtained. The signal is then processed to allow for background G3 facsimile equipment and level variations, and to preserve character size, then converted to binary levels for normal transmission, as a black/white image. It World-wide there are approaching 20 million (1991) compatible may be converted to amplitude bits for processing for pseudo half facsimile transceivers capable of interoperation using the Public tone/grey scale transmission. The original is then advanced Switched Telephone Network. Designs and implementations vary 1/3.85mm or 1/7.7mm for the next line to be scanned. If the line but the most popular scanning method is by CCD (charge coupled transmission buffers are full the scanning may then wait until further device) and printing by thermal head on heat sensitive paper. data is required. Figure 60.1 shows a block diagram of a G3 machine. Discrete LSI A second popular method of scanning uses CIS (Contact Image is often used for online signal processing, to ensure a manageable Sensor). This is a single line sensor assembly fitted close to the load for the main CPU which takes care of the user interface, paper at the document scanning point. It requires an array the full dialling functions, mechanism control housekeeping and reporting. width of the paper, but it saves the space taken up by the CCD The CCITT G3 recommendations include a number of options, for optical path. The copy is illuminated by LEDs (Light Emitting example fine resolution, MR coding, V29 modem, ECM. For these Diodes) within the unit and the radiated light from the area being 60/6 Facsimile transmission Signal Compressor/ Modem processor decompressor Sensor Phone Motor, Mechanism l