8/9/2019 Dev Com Tech Radio

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8/9/2019 Dev Com Tech Radio

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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 itstransmission (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 inamplitude (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 thesounds 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.