Telecommunications: Radio and Television

aerial -> tuner -> decoder -> amplifier ^ power supply ^ -> loudspeaker

picks up radio waves of many different frequencies and converts them into electrical signals

selects one particular frequency from the many received by the aerial

extracts the audio signal from the transmitted radio signal

increases the strength of the electrical signal

converts the electrical signal into sound

supplies extra energy for the amplifier

• changing the amplitude of a high frequency carrier wave according to the audio signal that is to be carried.
• this known as amplitude modulation (AM)

• in frequency modulation it is the frequency of the carrier wave that is changed according to the audio signal
• this produces a higher quality signal since interference has little effect on the frequency of the transmitted radio wave

• aerial -> tuner
• -> audio decoder -> audio amplifier -> loudspeaker
• |
• -> vision decoder -> vision amplifier -> picture tube

picks up television waves of many different frequencies and converts them into electrical signals

selects one particular frequency from the many received by the aerial

selects extracts the audio signal from the transmitted television signal

increases the strength of the electrical audio signal

converts the electrical signal into sound

extracts the vision signal from the transmitted television signal

increases the strength of the electrical vision signal

converts the electrical signal into light

to supply extra energy to the amplifiers

• consists of an electron gun situated inside an evacuted glass tube, which is painted with a special phosphor coating
• the electron gun fires a beam of electrons at the phosphor paint on the screen where the kinetic energy of the electrons is turned into a spot of light

• by moving the electron beam across the screen in a series of lines
• as the beam moves across the screen the brightness of the spot is altered by changing the number of electrons hitting each part of the screen
• a new picture is produced 25 times each seconds and because our eyes retain the image on the retina of the eye, each picture merges into the next
• since each picture is only slightly different from the previous one the picture appears to move

• TV signals
• the carrier wave is modulated to carry two synchronised signals, each signal is then extracted by a seperate decoder

• A colour television has three different coloured phosphor dots at each point on the screen.
• One electron gun fires at each colour and by altering the number of electrons fired at each dot they are lit up with varying brightness.
• This allows all the colours to be produced by colour mixing.

• red
• green
• blue