How Radio Works

Introduction:

•    Technically, radio is a small part of the electromagnetic spectrum , so-called because electromagnetic waves are driven across space at the speed of light by electric and magnetic forces. Gamma rays, x-rays, ultra-violet, visible light and infra-red are also parts of the same spectrum. They all travel at the identical speed but have different properties and uses, depending on their frequency or wavelength .              
• If equipment generating radio frequency energy (a transmitter) is connected to an antenna (or aerial) the energy is radiated in the form of radio waves. Some of the radiated energy can then be collected by another antenna which, when coupled to a radio receiver, enables a link to be made between the transmitter and receiver. Adding information to the radio carrier wave enables messages to be transmitted. These messages may take the form of television program-mes, voice messages, data or other forms of radio communication. Radio is an immensely versatile medium.
• The way in which radio waves propagate or travel through the atmosphere varies with the frequency or wavelength of the radio signal. In general, the lower the frequency the further the distance that radio waves will travel. As the frequency increases, the waves may be obstructed or deflected by hills and buildings. At extremely high frequencies, rainfall and other weather conditions can significantly limit the effective operating range of radio communications. These propagation characteristics mean that different bands of frequencies are suited to particular types of radio use. For example, for national and international broadcasting the long-wave (approximately 148-283 kHz) and medium-wave (approximately 526-1606 kHz) bands are used. At the higher frequencies such as VHF (Very High Frequency - 30 to 300 MHz) and UHF (Ultra High Frequency - 300 to 3000 MHz), where the effective transmission range is shorter, the bands are more suited to local broadcasting or local coverage for mobile radio systems. At higher frequencies it is possible to allocate wider channels (i.e., more bandwidth) and this allows more information to be transmitted per channel than at lower frequencies. For example, at VHF, because of the greater bandwidth available, high quality stereo music can be transmitted, but a typical channel in the long wave bands will support only a low quality music broadcast.

Basic radio block diagram:

The power supply (not shown) is connected to the pre-amplifier and power amplifier blocks.

• Microphone - a transducer which converts sound to voltage.
• Pre-Amplifier - amplifies the small audio signal (voltage) from the microphone.
• Tone and Volume Controls - adjust the nature of the audio signal. 
  The tone control adjusts the balance of high and low frequencies.
  The volume control adjusts the strength of the signal.
• Power Amplifier - increases the strength (power) of the audio signal.
• Loudspeaker - a transducer which converts the audio signal to sound.

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Radio Receiver System

 

The power supply (not shown) is connected to the audio amplifier block.

• Aerial - picks up radio signals from many stations.
• Tuner - selects the signal from just one radio station.
• Detector - extracts the audio signal carried by the radio signal.
• Audio Amplifier - increases the strength (power) of the audio signal. 
  This could be broken down into the blocks like the Audio Amplifier System shown above.
• Loudspeaker - a transducer which converts the audio signal to sound.

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Regulated Power Supply System

 

• Transformer - steps down 230V AC mains to low voltage AC.
• Rectifier - converts AC to DC, but the DC output is varying.
• Smoothing - smooths the DC from varying greatly to a small ripple.
• Regulator - eliminates ripple by setting DC output to a fixed voltage.

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Feedback Control System

 

The power supply (not shown) is connected to the control circuit block.

• Sensor - a transducer which converts the state of the controlled quantity to an electrical signal.
• Selector (control input) - selects the desired state of the output. Usually it is a variable resistor.
• Control Circuit - compares the desired state (control input) with the actual state (sensor) of the controlled quantity and sends an appropriate signal to the output transducer.
• Output Transducer - converts the electrical signal to the controlled quantity.
• Controlled Quantity - usually not an electrical quantity, e.g. motor speed.
• Feedback Path - usually not electrical, the Sensor detects the state of the controlled quantity.

Diagrams:

Videos:

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