Electromagnetic Waves, Voice Transmission, and Communication Technologies

Electromagnetic Waves

6. Wave: electromagnetic vibration propagating through space.

• Length (m): Distance from the beginning until it repeats.
• Width (m): Maximum height.
• Frequency (Hertz): Wave quantities per second.

Voice Transmission

7. Voice (microphone) → cable → electrical signal transmitter → antenna (emits waves) → wave → electrical signal → antenna captures → voice.

Am: Amplitude Modulated.
FM: Frequency modulation.

Digital Terrestrial Television (DTT)

8. Television is accessible to all with DTT, offering optional paid content.

• Eliminates image defects and snow effect.
• Improves picture quality and sound.
• Allows subtitle and language selection.
• Offers interactive and multimedia services.
• Enables real-time traffic, statistics, surveys, and trade.

Modern Communication Technologies

9. VoIP: Enables low-cost telephone conversations between network points.

WiFi: Uses 2.4 GHz radio communication for data transfer (11-54 Mbps), with extensions for higher speeds.

Bluetooth: Enables short-range data exchange between mobile and fixed devices.

Historical Context and Evolution

1. Morse Code, Radio, Television, Telephone, Thermionic valve.

2. Microphones:

• Piezoelectric crystal membrane (electrical sound signals).
• Piezoelectric crystal copper wire (electrical signals to sound).
• Headphones membrane.

4. Antennas: Communication between mobile and fixed devices.

Transmission Equipment: Issues phone waves.

Team Management: Coordinating with other devices.

Memory Effect: Batteries should be fully discharged to avoid shortening their lifespan.

5. a) Television History:

• Invented by John L. Baird.
• First image transmitted on October 2, 1925.
• Color television appeared in 1957.
• First broadcasts in Spain (Madrid) in 1956.
• Catalonia broadcasts in Catalan began on September 11, 1983.
• Private television (A3, Tele 5) in 1987.
• Canal 33 in 1988.
• Local television and Canal + (1994-1997).

5. b) Signal Types:

Analog: Image → ?
Arriba: Images and sound
Teletext: ?
Digital Image: Code → Binary (Example: 01011101)