Words and word combinations:

Continuous – непрерывный

a steady stream of water – постоянный поток воды

a garden hose – садовый шланг

is measured – измеряется

cycles per second – циклы в секунду

high-frequency sound waves – высокочастотные звуковые волны

low-frequency waves – низкочастотные волны

loudness – громкость

the short bursts of water – брызги воды

garden sprinkler – садовый разбрызгиватель

transmission medium – средства передачи

electrical pulses – электрические пульсы

digital data – цифровые данные

converting digital signals into analog – превращение цифровых сигналов в аналоговые

converting the analog signals back into digital – превращение аналоговых сигналов в цифровые

sending computer – отправляющий компьютер

receiving computer – принимающий компьютер

must be connected to a modem – должны быть соединены с модемом

both modems – оба модема

When we speak, we transmit continuous sound waves (fig.1), or analog signals, that form what we call ‘voice’. Analog signals could be compared to a steady stream of water coming out of a garden hose. These signals repeat a certain number of times over a certain time period- their frequency, which is measured in cycles per second, or hertz. Sometimes our voice sound high (composed of high-frequency sound waves) and sometimes our voices sound low (composed of low-frequency waves). Analog signals can also differ in amplitude, or loudness; a soft voice is at low amplitude. Telephone lines are currently an analog communications medium.

C ontinuous, or analog signal

Digital signals, in contrast, can be compared to the short bursts of water that shoot out of a timed garden sprinkler. These signals are discontinuous (discrete) pulses over a transmission medium (fig.2). Computers communicate with each other in streams of binary digits (bits) transmitted in patterns of digital signals- a series of on and off electrical pulses. For data to travel from one computer to another across the phone lines, the sending computer’s digital data must be converted into analog across the phone lines, the sending computer’s digital data must be converted into analog form and then recovered into digital form at the receiving end - modulation and demodulation.

Discontinuous, or digital signals

Modulation refers to the process of converting digital signals into analog form so that data can be sent over the phone lines. Demodulation is the process of converting the analog signals back into digital form so that the receiving computer can process them. The hardware that performs modulation and demodulation is called a modem (modulate/demodulate). The sending computer must be connected to a modem that modulates the transmitted data, while the receiving computer must be connected to a modem to demodulate the data. Both modems are also connected to the telephone lines.

Exercises:

1. Give Russian equivalents of the following phrases:

Continuous sound waves; could be compared; water coming out of a garden hose; can also differ, these signals are discontinuous; transmitted in patterns of digital signals; a series of ‘on’ and ‘off ‘electrical pulses; the process of converting digital signals.