Modem |
Acronym for "modulator demodulator". Electronic device used for data transmission. As far as computers are concerned this device is using phone lines or TV cables.
The principle is as follows: Let's say we want to send the series 01001110. (corresponding to the letter N in our example at the page ).The modem generates a wave which is flowing at a set frequency through the phone lines. It's called a carrier wave. We represent it with the following drawing:
Next we modulate this wave i.e. we change its shape with respect to the bits we want to send like this:
| 0 | 1 | 0 | 0 | 1 | 1 | 1 | 0 |
The receiving modem at the other end of the line can easily decode it (it's the "demodulator part") and transfer the value of the bits to the processor.
In the case of phone communications the principle is the same except the carrier wave is modulated by the voice. If you got ADSL the frequency that's being used is much higher than the one used to transfer voice signals thus the 2 transmissions can occur simultaneously without interference between them. Apart from the high speed of the ADSL this is a great advantage of it.
| Copyright 2003-2004 Jacques Lederer |