Senin, 05 April 2010



(tugas ini dibuat untuk melengkapi tugas development of communication technology pada sem 6)

1. Development of radion technology

• James Clerk Maxwell : developed the mathematical theory of electromagnetic waves.
• Heinrich Hertz : devised an apparantus for generating and detecting them.
• Guglielmo Marconi : recognizing the possibility of using these waves for a wireless communication system.
• 1901, Marconi : succeeded in sending the letter S across the Atlantic Ocean using Morse code.
• 1904, Sir John A. Fleming : developed the first vacuum electron tube which was able to detect radio waves electronically.
• 1906, Lee De Forest : invented the audion , three alement tube which was able to detect radio waves and also amplified them.
• 1906, the beginning of radio telephony and the transmission of music and speech. Reginald Fessinden succeed broadcasting a song “ O Holy Night” and reading a passage from the Bible. Became the first radio audio broadcast.
• 1913, Edwin H. Armstrong : patended the circuit for the regenerative receiver that long-range radio reception became practicable.
• 1920 : Station KDKA at Pittsburgh, the first commercial broadcasting station in the United States.
• 1922 : the world’s first regular wireless broadcast for entertainment from the Marconi Research Centre.
• Radio that combine transmitters and receivers are now widely used for communication.

2. Uses of Radio Waves
• To convey information from one place to another through the intervening media (air,space,nonconducting materials,etc) without wires.
• For the transmission of data in coded form
• Long-range radio signals enable astronauts to communicate with the earth from the moon and carry information from space probes as they travel to distant planets.
• Radio compass and radio time signals widely used for navigation of ships.
• To activated rocket and artificial satellite operation systems using radio signals.
• Cellular and cordless telephones are actually radio transceivers.

3. Transmission and Reception of Radio Waves

• For the propagation and interception of radio waves, a transmitter and receiver are employed. A radio wave acts as a carrier of information – bearing signals ; the information may be encoded directly on the wave by periodically interrupting its transmission (as dot and dash telegraphy) or impressed on it by a process called modulation.

Two most common types of modulation are:
o Amplitude modulation (AM)
o Frequency Modulation (FM)

Differences between AM and FM receivers are:
o FM minimizes noise and provides greater fidelity than amplitude modulation, which is the older method of broadcasting.
o In an AM transmission the carrier wave is constant in frequency and varies in amplitude (strength) according to the sounds present at the microphone.
o In FM, the carrier is constant in amplitude and varies in frequency.
o Wideband FM receivers are inherently less sensitive to noise.
o FM is also used in television sound systems.

• In its most common form, radio is used for the transmission of sounds (voice and music) and pictures (television). Television sends the picture as AM and the sounds as AM or FM (4,5 MHz).
Converted into electrical signal
Sounds and image ------- microphone/video camera ------ amplified ------ modulate a carrier wave ----- amplified ------ applied to antenna (converts the electrical signals to electromagnetic waves for radiation into space) ------ change it back to the form of electrical signals, and feed it to a receiver.