2.3. Connection with at

There is no mistake in the name of this device. The first reason to write it like this is that the name of it was made of two words – modulation and demodulation. The second reason is that people, who know computer and programming very well, often write computer [and not only] words like this if they’re made of more than one word [for example, ‘OutTextXY’].

2.3.1. Digital signal to analog

First principle of the work of modem has the name ‘modulation’. It sounds like this because all analog signals have their modulation – the sum of waves with low and high frequencies. The word ‘modulation’ also means ‘converting digital signal to analog’.

So, the first principle how to use is modulation. In the simplest point of view, modem takes the carrier tone [a kind of main sound – modem uses carrier tone to generate low or high frequency sounds] and modulates it – makes sounds from the bits. Look at the schemes 1 and 2 to see how the digital signal can be transformed to analog.

2.3.2. Analog signal to digital

Second principle of modem’s work has name ‘demodulation’. As you decide, this is an opposite of the first. The word ‘demodulation’ means ‘converting analog signal to digital’.

In the simplest point of view, modem takes the sound, compares it with the carrier tone to separate high and low sounds and demodulates it – makes sounds from the bits using carrier tone as an etalon.

Look at the schemes 2 and 1 to see an example of transforming the analog signal to digital.

2.3.3. Using of modulation and demodulation

As you have head, the processes of modulation and demodulation are used in modems. Modems are the main representatives of the devices that use modulation and demodulation. Only one modem can do many things.

It can be used in Dial-Up Networking to have the possibility of exploring the WorldWideWeb – Internet.

Another use of modems is to connect two computers with the ability to e-talk in real-time mode and to send and get files. It is very good because in our country nobody wants to spend his own money using the Internet and if somebody has a file, he can send it to anybody without spending money.

And the last example is IP-Telephony. It’s a phoning using the Internet. It is used if you need to call to another city or country without paying much money. You just pay for the Internet access and talk via some special servers.

Exercise 5

Answer the following questions:

1. What are Digital Technologies?

2. Why do we use DT?

3. What do you know about Digital signal?

4. What is the data in DT based on?

5. Is bit a digital signal or a digital information?

6. How many bits are there in a unit?

7. How can data be stored in computers?

8. What are clusters?

9. What are the principles of modem’s work?

10. Another use of modems is connected between two computers with the ability to e-talk, isn’t it?