GCSE

System Diagram

Tuner

A Digital TV Tuner

Devices that pick up radio transmissions need a tuner. This can be a stand-alone device or more often it is built into a larger system Examples of tuners can be found in ...

• Radios
• TV Sets
• Satellite Receivers
• Mobile Phones
• SatNav receivers

What the tuner does ...

• It amplifies the weak radio signals.
• It selects the wanted station and filters out all the others.
• It demodulates the radio signal giving audio, video or data signals.

Amplifier

Audio Amplifier

Quite a lot of power is needed to drive loudspeakers. A small radio might have a 0.25 Watt amplifier. Some TV surround sound systems have powers up to 100 Watts. The function of the amplifier is to increase the small input signal up to a level sufficient to drive the loudspeakers.

Audio Frequencies

Amplifiers need to work well for the whole range of Audio Frequencies.

• 20 to 20000 Hz is needed for top quality audio, typical in entertainment systems.
• 20 to 15000 Hz is the range transmitted by FM radio stations. This still sounds good.
• 50 to 4000 Hz is typical for AM radio. This sounds a lot less nice.
• 300 to 3000 Hz is the minimum needed for clear voice communication. Telephone calls use this frequency range.

Microphone

Electret Microphone

• This is an input transducer.
• It converts energy in the form of pressure waves in air into electrical energy.
• The voltage produced by the microphone is proportional to the air pressure.

Loudspeaker

Woofer, Midrange and Tweeter Loudspeakers

• This is an output transducer.
• It converts electrical energy into movements of a paper cone which produces pressure waves in the air.
• The air pressure produced by the loudspeaker is proportional to the voltage of the electrical signal.

MP3 or similar Players

Low Cost MP3 Player

• Music is stored digitally.
• This means it is stored in the memory chips as binary zeros and ones.
• To play pack the music, the digital data must be converted into an analogue signal.
• A digital to analogue converter (DAC) does this.
• The analogue music signal is amplified and fed to the loudspeakers.

CD and DVD Players

Audio CD Player

• Compact disks, digital versatile disks and blu-ray disks all contain digital data.
• A DAC or digital to analogue converter produces analogue audio and video signals.
• The audio is amplified and sent to loudspeakers or headphones.
• The video signal is sent to the display screen.

CD and DVD Recorders

DVD Recorder

• To record audio and video, the analogue signals must be converted into digital.
• An analogue to digital converter (ADC) does this conversion.
• The digital data (zeros and ones) is recorded onto the CD or DVD.

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