Design And Construction Of Amplitude Modulation Receiver

INTRODUCTION
1.1 BACKGROUND OF THE STUDY
Modulation is the process by which voice, music and other “intelligence” is added to the radio waves produced by a transmitter. The different methods of modulating a radio signal are called modes. An unmodulated radio signal is known as “A Carrier” [1]. When you hear “dead air” between songs or announcements on radio station you are “hearing” the carrier. While a carrier contains no intelligence, you can tell it is being transmitted because of the way it quiets the background noise on your radio [2].
A device that performs modulation is known as a modulator and a device that performs the inverse operation of a modulator is known as a demodulator (sometimes detector or demodulator). A device that can do both operations is a modem. [1], [3] In amplitude modulation, the strength (amplitude) of the carrier from a transmitter in varied according to how a modulating signal varies. [4].
When you speak into the microphone of an AM transmitter (broadcasting on a frequency between a frequency range of 530 to 1700 KHz), the microphone converts your voice into a varying voltage which is been received.[2].
Amplitude modulation results in three separate frequencies being transmitted:
• The original carrier frequency
• A lower sideband (LSB) below the carrier frequency
• And an Upper sideband (USB) above the carrier frequency. [4]
The side bands are “mirror images” of each other and contain the same intelligence. [5]. When an AM signal is received, these frequencies are combined to produce the sounds you hear via an AM receiver.
The AM Broadcast service in Nigeria and many other countries is implemented on 10 kHz channel steps with center frequencies 540 kHz through to 1700 kHz, and carrier power levels from 250 watts to 50 kilowatts (2). The AM receiver used in this work is a AM receiver that can pick up any AM radio station. An AM receiver detects amplitude
variations in the radio waves at a particular frequency, converts a received amplitude- modulated wave back to the original source information, which is the process of demodulation, It then amplifies changes in the signal voltage to drive a loudspeaker or earphones (1), in other words AM receiver is capable of receiving, amplifying and demodulating an AM radio wave (1).The aim of this work is to design and develop a simple, affordable AM receiver.

1.2 OBJECTIVE OF THE STUDY
The objectives of this study are:
• To understand the theoretical foundations of Analog Communications as well as Amplitude Modulation (AM)
• To design an AM receiver using locally available materials
• To observe the real-time music transmission for AM modulated signal

1.3 SCOPE OF THE STUDY
The scope of this study is on the AM receiver. The AM Radio project was built with only 2 transistors. The variable capacitor (VC1) in parallel with the coil (L1) acts as a tuneable resonant circuit. This “tank” circuit can be adjusted at the desired AM frequency.

1.4 SIGNIFICANCE OF THE STUDY
This study will enable students in an introductory electronics class to build, observe, and understand a simple and reliable receiver. The design is simple enough to be consistently functional in an introductory laboratory environment and performed well on student bread boards. This approach is repeatable, affordable, and provides the students with an effective hands-on demonstration of a electronics design.

1.5 METHODOLOGY
To achieve the aim and objectives of this work, the following are the steps involved:
i. Study of the previous work on the project so as to improve it efficiency.
ii. Draw a block diagram.
iii. Test for continuity of components and devices,
iv. Design and calculation for the work was carried out.
v. Studying of various component used in circuit.
vi. Construct the whole circuit.
vii. Finally, the whole device was cased and final test was carried out.

1.6 LIMITATION OF STUDY
As we all know that no human effort to achieve a set of goals goes without difficulties, certain constraints were encountered in the course of carrying out this project and they are as follows:-
i. Difficulty in information collection: I found it too difficult in laying hands of useful information regarding this work and this course me to visit different libraries and internet for solution.
ii. Financial Constraint: Insufficient fund tends to impede the efficiency of the researcher in sourcing for the relevant materials, literature or information and in the process of data collection (internet).
iii. Time Constraint: The researcher will simultaneously engage in this study with other academic work. This consequently will cut down on the time devoted for the research work.

1.7 PROJECT ORGANISATION
The work is organized as follows: chapter one discuses the introductory part of the work, chapter two presents the literature review of the study, chapter three describes the methods applied, chapter four discusses the results of the work, chapter five summarizes the research outcomes and the recommendations.