Lesson Notes By Weeks and Term v4 - SHS 3
ELECTRONIC COMPONENTS AND CIRCUITS
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ELECTRONIC COMPONENTS AND CIRCUITS
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Subject: Applied Technology
Class: SHS 3
Term: 2nd Term
Week: 20
Grade code: 2.5.2.LI.11
Strand code: 4
Sub-strand code: 2
Content standard code: 2.5.2.CS.1
Indicator code: 2.5.2.LI.11
Theme: ELECTRICAL AND ELECTRONIC TECHNOLOGY
Subtheme: ELECTRONIC COMPONENTS AND CIRCUITS
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Welcome, learners! Every day, we listen to our favourite radio stations like Joy FM, Peace FM, Citi FM, or GBC Radio. We hear music, news, and exciting discussions. But have you ever wondered how the voice of the presenter in the studio in Accra travels through the air and reaches your radio set in Kumasi, Tamale, or even your village? The magic behind this is radio transmission. The device that sends out these signals is called a transmitter. Today, we will explore the two most common types of transmitters used in radio broadcasting: AM (Amplitude Modulation) Transmitters and FM (Frequency Modulation) Transmitters.
A. The Basics: What is Modulation and Why is it Necessary?
Before we discuss transmitters, we must understand modulation. Audio Signal: The sound from a microphone (like a presenter's voice or music) is a low-frequency, low-energy electrical signal. If we try to transmit this signal directly with an antenna, it will not travel far—maybe only a few meters. It's like trying to throw a single piece of paper across a football field; it won't go far. Carrier Wave: To solve this, we generate a high-frequency, high-energy wave called a carrier wave. This wave has no information on its own, but it can travel very long distances. Think of this as a heavy stone you can throw far. Modulation: Modulation is the process of "superimposing" or "adding" the low-frequency audio signal onto the high-frequency carrier wave. We are essentially wrapping our paper (information) around the stone (carrier) so it can be thrown a long distance. Transmitter: A transmitter is an electronic device that performs this modulation, amplifies the resulting signal to a very high power, and then sends it out into the air through an antenna as an electromagnetic wave.
There are two main ways to "add" the information to the carrier wave: by changing its amplitude (AM) or by changing its frequency (FM). B. The AM (Amplitude Modulation) Transmitter
In Amplitude Modulation, the amplitude (strength or height) of the high-frequency carrier wave is varied in accordance with the audio signal. The frequency of the carrier wave remains constant. Imagine a wave with a constant height. When the audio signal is strong (loud sound), the height of the carrier wave increases. When the audio signal is weak (soft sound), the height of the carrier wave decreases.