Radio is a popular electronic device that is used to listen to music, speeches, and weather bulletins, etc. Radio communication involves a radio transmitter and a radio receiver. Radio broadcasting works by translating sounds into electromagnetic waves called radio waves. The radio is one of the outstanding developments of the 20th century with modern radio sending and receiving equipment. A radio station sends the radio waves through the air. A radio picks up the waves and changes them into sound in a radio station. A microphone picks up speech music and other sounds of a radio program. The microphone creates an electric current or signal that corresponds to the pattern of the sound waves. The signal is sent to a transmitter there it’s combined with another electric current called a carrier signal. The combined signal is sent to an antenna which broadcasts it as radio waves of an assigned frequency. The radio waves carry the sound information as either FM signals or AM signals. FM signals can reach ground-based receivers only as far as the horizon. AM signals can reach receivers beyond the horizon because may bounce off a layer of the atmosphere but AM signals are more susceptible to static than FM signals. The radio antenna picks up all broadcast signals that reach it the listener adjusts the radios tuner to make the receivers sensitive to the frequency of a particular station. When radio waves reach a radios antenna they produce an electric current within it. This current contains the sound information that was carried in the radio waves.
History of Radio:
Radio you know that old dusty thing that sits up at the front of your car or in the corner of your house most of us are too occupied with television or iPods or video games to really listen to it. But the impact it has had on our world is immense. It all started in 1873 when James Clerk Maxwell showed mathematically that electromagnetic waves could travel through air before long in 1888 Heinrich Hertz demonstrated Maxwell’s theory by demonstrating that someone could produce and detect electromagnetic radiation then in 1892 Nikola Tesla used Maxwell’s mathematic findings to demonstrate the sending and receiving a radio frequency energy. He proposed that this method could be used for sending and receiving information. But it was Guglielmo Marconi who built the first wireless transmitter in 1896 which was capable of sending signals up to one and a half miles. He then proceeded to develop the world’s first transatlantic radio communication service between Clifton Ireland and Newfoundland. In 1901 the next evolution in radio technology was the invention of the spark-gap transmitter. This device allowed for the production of the first commercially available radio sets. But the spark gap radios were plagued with problems mainly electrical interference. These were greatly improved with the invention and production of crystal radio sets the crystal sets were the first widely produced and widely used radio sets in America. These crystal sets were widely used in most American homes by the 1920s it was the American families connection to the rest of the country. This was fantastic but there was still a problem that needs to be fixed up to this time all radio was being broadcast using AM waves. AM stands for amplitude modulation but the problem was that AM radio is medium range and is prone to be blocked by urban structures. But in 1933 Edwin H Armstrong invented FM radio FM stands for frequency modulation. This type of broadcasting method uses a wavelength that is less prone to static and blockage. It also has a longer range with the invention of FM radio only needed one more evolution to become what you know today that last advancement was the transistor radio the transistor radio had particular advantages over the old crystal sense the transistor sets were much cheaper than the crystal ones use less power at a smaller size and had a very long life span.
It is possible to establish communication instantaneously from any place at any time the radio brings into the home the schoolroom the hospital and the office music by leading artists drama by outstanding actors speeches by men in public life and news of world events together with weather and market reports commercial and military aviation depend on radio. The radio operator communicates with other planes and with ground bases.
Working of the Radio:
First of all the sound waves produced by the announcer are picked up by the microphone which is one element in the transmitter circuit. This circuit requires a source of electrical energy shown here as a primary cell. The moving particles represent electrons as they flow in a direct current all sound sources set the molecules of air into vibration in such a manner as to produce waves which travel through the air. In the radio studio these waves strike the diaphragm of a microphone as the molecules in the sound wave moved back and forth they set the diaphragm into vibration. In the carbon microphone each time the sound waves push the diaphragm in it presses upon a mass of carbon granules and reduces their resistance to the flow of electricity. Thus more electrons can flow in the circuit each time the diaphragm moves out the carbon granules separate the resistance to the current is increased. Now fewer electrons can flow in the circuit thus in the microphone. The movement of the diaphragm regulates the flow of electrons in the transmitting circuit and changes the steady direct current into a pulsating direct current although most sounds are complex. We are illustrating this voice current is a pure tone at the top. We now trace out a curve to represent the pulsating direct current all these processes are sloped down. In these animated drawings in order to show clearly how the electrons move in the circuit in this schematic transformer the primary coil which is a part of the transmitter circuit is it the lift and the secondary coil is at the right as the current increases in the primary coil it builds up a magnetic field which sweeps across the loops of the secondary and starts a flow of electrons. When current in the primary decreases the magnetic field collapses and the lines of force cut back through the secondary coil. Now electrons in the secondary flow in the opposite direction when the magnetic field builds up the secondary current flows in one direction. When the magnetic field collapses the secondary current flows in the opposite direction a current which flows in one direction and then reverses to flow in the other direction is called an alternating current at the top. We now trace out occurred to represent the alternating current in the secondary when the curve crosses the zero line. It shows that the current is changing direction the monitor in the control room controls the quality of the sound as it goes on the air the monitor balances the sound from the various sources to achieve the desired blend. The voice current or the audio frequency current as it comes from the transformer is amplified by vacuum tubes such as these let us retrace the main events in the audio frequency circuits the microphone brings about a pulsating direct current. The transformer changes this to an alternating current vacuum tubes amplify this alternating current which then goes to the modulator tube. The broadcasting station uses a high frequency current called the carrier wave to transmit the message a generator supplies a direct current to the oscillator tube. The oscillator tube changes this direct current to a higher frequency alternating current of several hundred thousand cycles per second. The box below this oscillator tube contains a quartz crystal which keeps the carrier wave at a constant frequency. This radio frequency current also goes to the modulator tube. This is the modulator tube in which the radio frequency current is modulated by the audio frequency current. In the modulator tube the audio frequency current shown at the lower left modifies the radio frequency current shown above according to the strengths and the frequency of the voice current this is called modulation note. However that the modulated wave is still a radio frequency current the modulated radio wave now goes to the power tube this is the primary power source of the transmission station. Where current comes in at a high voltage these transformers convert the incoming current to a high voltage necessary to secure dependable long-range sending these vacuum tube rectifiers convert this alternating current into a direct current power tubes operating on this high voltage are used to amplify the modulated waves received from the modulator to several power tubes are used when great sending power is desired. The current from the power tubes goes to this antenna coupling unit which is essentially a transformer the current is carried by two insulated copper tubes one within the other to the antenna to review the events the modulated radio frequency current coming from the modulator goes to the power tubes the power tubes amplify this current which then goes to the antenna.
This antenna consists of two steel towers and a central wire supported by a cross cable between them radio waves are set out in all directions. Thus from the power tube the modulated radio waves go to the antenna the radio messages leave the antenna as electromagnetic wave and travel out into space with the speed of light for special events. This portable device broadcasts by shortwave to a local station for rebroadcast or it may be even used as a receiver. Let us recapitulate the events in radio broadcasting sound waves strike the diaphragm of the microphone a pulsating direct current is set up in the transmitter circuit this is changed by the transformer to an alternating current which is amplified and sent to the modulator tube a generator delivers a direct current which the oscillator tube changes to a high frequency current which is fed into the modulator tube where it is modified by the audio frequency current coming from the microphone. The modulated current is boosted by the power tube which is coupled to the antenna here. The radio frequency sets up electromagnetic waves which travel out into space with a speed of 186,000 miles a second. When these waves strike the antennae of a receiving set this entire process is reversed. We hear sound originating at that very moment hundreds or even thousands of miles away.
Sound waves are produced by vibrations music speech or weather bulletin consists of sound waves. The information transmitted is called intelligence. Sound waves are converted into electrical signals called audio frequency waves or AF waves. Microphones convert the vibrations into AF. There is a thin firm called diaphragm in microphones. The diaphragm vibrates by sound waves which are transferred to a crystal. The crystal is generally made from quartz that is a crystalline form of silicon dioxide. These crystals produce electrical signals when subjected to stress the variations in AF are according to the variations in sound waves. AF signals are strengthened by electronic devices this is known as amplification. The amplified AF signals cannot travel long distances. Electromagnetic waves of wave length one meter to one kilometer act as transport vehicles for the AF signals.
Electromagnetic waves carrying the AF signals are called carrier waves or radio frequency waves or RF waves. RF waves are produced using oscillator coils in the transmitter h-hour Hertz has contributed in production of radio waves of required frequency. Each transmitter has its own vehicle that is its own RF waves.
A radio station is recognized by this frequency. The process of superimposing AF signals on RF wave is called modulation. The modulated waves are further amplified and transmitted by transmitting towers or antennae. The RF wavelengths in the range of 10 meter 200 meter get reflected by the ionosphere of the earth.
Advantages of the Radio communication:
The major advantage of radio communication is that the transmitted modulated waves cover large distances FM stations or TV stations use high frequency waves which pass through ionosphere and are not bounced. Relay stations or satellites are needed for long-distance communication of such stations.
Frequency of the station can be calculated if the wavelength is given.
Velocity is equal to wavelength multiplied by frequency.
V= λ × f
Frequency is equal to velocity divided by wavelength velocity.
V= 3 × 108m/s
Suppose the wavelength of a station is 300 meter does frequency of the station is 300 million divided by 300. Hence the frequency of the radio station is 10 raised to 6 Hertz or 10 raised to 3 kilo Hertz.
f = 106Hz
There are many receiving sets the radio should be tuned to the station to listen. There is a built-in antenna the antenna receives the modulated waves detector separates RF from AF signals this process is called demodulation the AF signals are amplified and fed to the speaker to reproduce the original sound. A speaker works in a reverse manner of the microphone the coil starts vibrating when AF signals are passed through it the vibrations are transferred to a diaphragm to produce sound waves.
Uses of Radio:
Radio principles are also used in blind flying on a radio beam the Coast Guard in the Navy in their constant vigilance are guided at all times by two-way radio communication with other ships and with their bases of operation army tank operations are directed by radio the tank commander is in radio communication with the tank crews under his command as well as with the field headquarters likewise every unit of the army uses portable radios to receive orders from instant information to their command posts let us follow through the steps and the processes in transmitting or sending radio messages.