Modern Radio Receiver

A. Radio is the transmission of signals through free space by electromagnetic radiation of a frequency significantly below that of visible light, in the radio frequency range from 30 kHz to 300 GHz. These waves are known as radio waves. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space. Information is carried by systematically changing (modulating) a particular property of the radiated waves, such as their amplitude, frequency, phase or pulse width. When radio waves strike an electrical conductor, the oscillating fields induce an alternating current in the conductor. The information in the waves can be extracted and converted back into its original form.

B. Radio systems used for communication include the following elements: a transmitter, an antenna, a receiver. A wide range of techniques can be applied for implementing each process, their use depending on the communications purpose.

C. A transmitter is one of the key components of the system. The transmitter contains a source of electrical energy producing alternating current of a required frequency and a system for modulating some property of the produced energy to impress a signal on it. This modulation might be as simple as turning the energy on and off, or altering more subtle properties such as amplitude, frequency, phase or combinations of these properties. The transmitter sends the modulated electrical energy to a tuned resonant antenna, which transforms the rapidly changing alternating current into an electromagnetic wave that moves through space.

D. Radio uses two basic modulation techniques: amplitude modulation and frequency modulation. Amplitude modulation of a carrier wave works by varying the strength of the transmitted signal in proportion to the information being sent. For example, changes in the signal strength can be used to specify the sounds reproduced by a speaker or the light intensity of television pixels. Frequency modulation, as its name suggests, varies the frequency of the carrier. The instantaneous carrier frequency is directly proportional to the instantaneous value of the input signal. Digital data can be sent by shifting the carrier’s frequency among a set of discrete values. This technique is known as frequency-shift keying.

E. An antenna (or aerial) is an electric device, which converts electric current into radio waves, and vice versa. It is usually used with both a transmitter and receiver. In transmission, a radio transmitter applies an oscillating radio frequency current to the antenna terminals, and the antenna radiates this energy as electromagnetic waves. In reception, an antenna intercepts some of the electromagnetic wave power to generate a tiny voltage at its terminals that is applied to a receiver for amplifying. A tuned receiving antenna captures some of the electromagnetic wave energy and returns it to the form of oscillating electrical currents. At the receiver, these currents are demodulated, i.e. converted to a usable signal form by a detector. The receiver is “tuned” to respond preferentially to the desired signals and reject undesired ones.

F. A radio receiver picks up its input from an antenna, uses electronic filters to separate a required radio signal from all other signals captured by this antenna. Then, it amplifies the signal to a level suitable for further processing. Finally, the receiver converts the signal through demodulation and decoding into a form usable for the consumer, namely sound, pictures, digital data, measurement values, navigational position, etc.

G. Early radio systems relied entirely on the energy collected by an antenna to produce signals. Radio became more effective after the invention of the vacuum tube and later the transistor that allowed amplifying weak signals. The first uses of radio were maritime intended for sending telegraphic messages using Morse code between ships and land. Nowadays radio takes various forms, including wireless networks and mobile communications, as well as radio broadcasting. Radio plays a significant role in the modern world due to a great number of its applications ranging from walkie-talkie children’s toys to controlling space vehicles.

V. Are the following statements true or false according to the text? If they are false, explain why.

1. The transmission of signals by radio is feasible only through wires.

2. To carry information one of the features of radio waves is systematically changed or modulated.

3. The number of components the radio system contains is different depending on the communication purpose.

4. The transmitter sends signals without any processing.

5. Radio broadcasting is performed by two methods known as amplitude modulation and frequency modulation.

6. An aerial is an electronic device that is used for transmitting signals.

7. The major function of a receiver is to select a wanted radio signal and demodulate it into a usable form.

8. At present radio does not play any significant role since the technology is out dated?

VI. Ask questions to the following answers.

1. The transmission of signals through free space.

2. Through oscillating electromagnetic fields.