Communications | Physics for GCSE/IGCSE - Year 11 PDF Download

Communications with Satellites

• Geostationary and polar orbiting (low orbit) satellites are both utilized for communication purposes.

Geostationary Satellites

• Geostationary satellites orbit above the Earth’s equator. The orbit completes in 24 hours.
• These satellites are positioned at a height of 36,000 km above the Earth's surface, significantly higher than polar satellites.
• This orbit is ideal for radio and telecommunication broadcasting worldwide due to its high altitude.

Polar Orbits

• Characterized by orbits around Earth's north and south poles.
• Located much lower than geostationary satellites, approximately 200 km above sea level.
  • Utilized for weather monitoring, military purposes, and Earth surface imaging.
  • Offer shorter signal delays compared to geostationary orbits, ensuring clearer signals and images due to their lower altitude.
  • However, limited for single orbit use due to the need for multiple satellites for continuous coverage.

Systems of Communications

• Long wave electromagnetic radiation is vital for various communication systems, such as 
  • Mobile phones, wireless internet, and satellite television (using microwaves).
  • Bluetooth, terrestrial television signals, and local radio stations operate on radio waves.
  • Optical fibers use visible or infrared waves for communication.

Radio Waves

• Radio waves are instrumental in Bluetooth connections, terrestrial television broadcasts, and local radio transmissions.
• They can transmit signals effectively over short distances.

Visible and Infrared Waves

• Visible and infrared waves are harnessed in optical fibers for high-speed data transmission.

Differences in Wavelengths

• Radio station signals are transmitted at longer wavelengths compared to terrestrial television signals.
• In hilly regions, radio signals may be received while terrestrial TV signals might not, due to radio waves' better diffraction around obstacles.

Why Radio Signals Diffraction Around Hills

• Radio signals are more prone to diffraction around hills compared to TV signals.

Understanding Diffraction

• Diffraction occurs because radio signals typically have wavelengths around a kilometer.
• This wavelength similarity to the size of hills enables diffraction, allowing radio signals to reach beyond the line of sight of the transmitter.
• In contrast, TV signals, with different wavelengths, are not diffracted in the same way.

Implications of Similar Wavelengths

• Due to this wavelength similarity, radio signals can reach locations that are not directly in the line of sight of the transmitter.
• TV signals, with different wavelength characteristics, do not exhibit the same diffraction phenomenon.

Bluetooth Communication

• Bluetooth technology utilizes radio waves to transfer data wirelessly between electronic devices like phones and speakers.
• Compared to radio or television signals, Bluetooth signals have shorter wavelengths, enabling high-speed data transmission.
• Bluetooth is effective over short distances, typically within a household, as the signals can pass through walls but get weakened in the process.

Signal Strength and Reach

• Due to their shorter wavelengths, Bluetooth signals are optimal for short-range communication.
• This feature allows them to penetrate obstacles like walls, though with a decrease in signal strength.

Microwaves

• Microwaves play a crucial role in transmitting signals across vast distances.
• These signals are utilized for communication with satellites and are integral in various technologies such as mobile phones, wireless internet, global satellite television, and Earth monitoring systems like weather forecasting.
• Similar to radio waves, microwave signals benefit from unobstructed paths to prevent diffraction, ensuring clearer communication.

Application in Satellite Communication

• Microwaves are specifically employed to establish links between ground stations and satellites.

Mobile Communication Networks

• Ground-based mobile communication networks rely on microwave transmitter masts to relay signals efficiently.
• Proper spacing of these masts is crucial to avoid signal diffraction due to obstacles like hills or the Earth's curvature.

Key Concepts About Microwaves

• When microwaves are transmitted from a dish, the wavelength should be small compared to the dish diameter to reduce diffraction. Moreover, the dish must be constructed from metal to effectively reflect microwaves.
• Mobile phones and wireless internet utilize microwaves because they are not refracted, reflected, or absorbed by the atmosphere or ionosphere. This property enables satellites to relay signals globally, ensuring 24/7 communication. Additionally, microwaves can penetrate most walls and require only a short aerial for transmission and reception.

Role of Metal in Microwave Transmission

• Metal dishes are crucial for transmitting microwaves efficiently. They reflect microwaves effectively, aiding in the reduction of diffraction and ensuring clear signal transmission.

Advantages of Microwaves in Communication

• Satellites relay signals globally, facilitating continuous communication worldwide.
• Microwaves can penetrate most barriers like walls, making them suitable for various communication applications.

Optical Fibres

• Optical fibres, whether utilizing visible light or infrared, play a crucial role in cable television and high-speed broadband services.
• These fibres leverage the transparency of glass to visible light and certain infrared wavelengths, which are ideal for high data transmission rates owing to their high frequencies.

Transparency and Data Transmission

• Glass's transparency to visible light and specific infrared wavelengths allows for efficient data transmission.
• Visible light and short-wavelength infrared possess the capability to transmit data at high rates due to their frequencies.

Functionalities

• Visible light and certain infrared wavelengths enable optical fibres to transmit cable television and high-speed broadband signals effectively.