ABSTRACT: The early transmitter for radio broadcasting is so big and bulky that they do occupy numerous spaces. The circuitries are mainly designed with valves, which are big in sizes. With the advent of semiconductor materials such as transistors electronic equipment are now becoming miniaturized such that small transmitters are now becoming handy and compact. In line with this we choose to design a complete radio broadcasting equipment that is compact and existence of semiconductor materials. The system units are of two categories namely: audio console for the processing and mixing of musicals is basically a condenser microphone. The transmitter unit is where the center frequency is provided. All these were designed to be in compact and small manner. This project is aimed at serving a community using a small and compact radio broadcasting equipment with a power watt of 1 watt a community of 1 kilometer in radius should be covered comfortable and the audio production very clear unlike the common noisy FM microphone project.
TABLE OF CONTENT
CHAPTER 1 TRANSMITTER FUNDAMENTALS
AND TYPES OF MODULATION
1.1 Transmitters fundamental
1.2 Modulations (analog and digital)
1.3 Amplitude modulation
1.4 Frequency modulation
1.5 Method of fm
1.6 Modulation overview
1.61 Basic reactance modulator
1.62 Theory of reactance modulator
1.70 Types of reactance modulator
1.7.1 Varacto diode modulator
CHAPTER 2 AMPLIFIER EXPLANATIONS
2.10 Amplifier explanations
2.20 Class of amplifier
2.21 Class of amplifier
2.22 Class B amplifier
2.23 Class AB amplifier
2.24 Class c amplifier
2.30 Oscillators
2.31 Types of oscillators
CHAPTER 3.0
TRANSMISSION LINE
3.10 FUNDAMENTALS
3.30 Types of transmission lines
3.31 Rectangular wave guide
3.32 Circular wave guide
3.33 Ridge Wave guide
3.34 Optical fiber
CHAPTER 4
POWER SUPPLY
4.1 Stages of power supply
4.2 Audio console power supply
4.3 Transmitter power supply design
CHAPTER 5 AUDIO CONSOLE UNIT
5.1 Audio console transducer
5.2 Audio console pre-amp stage
5.3 Audio console power amp stage
5.4 Audio console control/mixer
5.5 The operation of the audio console
CHAPTER 6 TRANSMITTER AND ANTENNA DESIGN
6.1 Oscillator stage design for transmitter
6.2 Buffer/power amplifier design
6.3 Tank circuit design
6.4 Antenna design
6.41 Types of antenna and application
6.42 Antenna matching network
6.43 Antenna design
CHAPTER 7 COMPONENT DESCRIPTION AND CONSTRUCTION
7.10 LM 386-power amplifier
7.11 Capacitor
7.12 Transistor
7.2 Specification
7.3 Construction and soldering
7.4 Precautions taken during soldering
7.5 Troubleshooting
7.6 Transmitter strip board
7.7 Audio console strip board
RECOMMENDATION
CONCLUSION
REFERENCE:
LIST OF FIGURES AND DIAGRAM
Fig 1.4 Information signal
Fig 1.62 Reactance modulator circuit
Fig 1.7 Reactance modulator elements
Fig 1.7 Diagram of transistor reactance modulator
Fig 1.8 Varactor diode modulator
Fig 2.1 Amplifier configuration
Fig 2.21 Class a wave form representation
Fig 2.22 Voltage current characteristic of class b amp
Fig 2.3 Block diagram of an oscillator
Fig 3.2 Balanced line
Fig 3.22 Unbalanced wire – line
Fig 3.3 Method of wave propagation in a waveguide
Fig 3.31 Te10 mode in a rectangular waveguide
Fig 3.32 Circular waveguide
Fig 3.33 Rectangular waveguide/ ridge
Fig 3.4 Optical fiber cable
Fig 4.1 Power supply block diagram
Fig 4.2 Audio console power supply regulator
Fig 4.3 Transmitter power supply
Fig 5.2 Audio console pre-amp
Fig 5.3 Audio console power amp
Fig 5.4 Audio console control/ mixer
Fig 6.1 Oscillator stage
Fig 6.2 Buffer amp/power amp
Fig 6.3 Tank circuit
Fig 6.42 Antenna matching network
Fig 7.1 LM 386 (power amp)
Fig 7.11 Capacitor
Fig 7.12 Transistor
Bill of quantity
Block diagram of audio console
Block diagram of transmitter
Audio console schematic
Transmitter schematic
Transmitter casing
Audio console casing
This our project work is all about design and construction of a complete radio broadcasting equipment that is compact and miniaturized. It is capable of delivering a power output of 1 watt and assumed to cover a distance of 400 meters ie 200 meters radius depending on obstructions.
The transmitted signal is frequency modulated stays constant and its frequency varies according to the amplitude variations of the audio signal. When the input signals amplitude increases (ie during the positive half cycle) the frequency of the carrier increases too, on the other hand when the input signal decreases in amplitude (negative half-cycle or no signal) the carrier frequency decreases accordingly.
The output frequency of the transmitter is adjustable from 88 to 108 MHZ, which is the FM band that is used for radio broadcasting. The circuit as we have already mentioned consist of four stages. Three RF stages and one audio preamplifier for the modulation. The first RF stage is an oscillator is controlled by LC network L-C, C is there to ensure that the circuit continues oscillating and C adjusts the coupling between the oscillator and the next RF stage which is an amplifier. This is built around TR2 which operates in clas c and is tuned by means of L and C. the last RF stage is also an amplifier built around TR3 which operates in class c the input of which is tuned by means of c and l. From the output of this last stage which is tuned by means of l-c is taken then the output signal which through the tune circuit l-c goes to the aerial.
The circuit of the preamplifier is very simple and is built around TR4. The input sensitivity of the stage is adjustable in order to make it possible to use the transmitter wit different input signals and depends upon the setting of VRI. As it is the transmitter can be modulated directly with a piezoelectric microphone, a small cassette recorder etc. it is of course possible to use an audio mixer in the input for more professional results which we did
CHAPTER ONE
TRANSMITTER FUNDAMENTAL AND TYPES OF MODULATION
1.1 TRANSMITTER FUNDAMENTALS
The AM transmitter generates such high power that it’s prime requirement is efficiency. Amplitude modulation can be generated at any point after the radio frequency source as a matter of fact, even a crystal oscillator could be amplitude modulated except that this would be an unnecessary interference with its frequency stability. If the output stage in a transmitter is plate modulated the system is called high-level modulation.
An AM transmitter which may be either low level or high level modulated have a stable RF source and buffer amplifier followed by RF power amplifier. The audio voltage is processed or filtered so as to occupy the correct bandwidth and compressed somewhat of reduce the ration of maximum to minimum amplitude.
In IM transmitter, the prime requirement of an FM system is a variable output frequency, with the variation proportional to the instantaneous amplitude or the modulation voltage.
The power and auxiliary stages of FM transmitter are similar to those in AM transmitter except that FM has an advantage, since it is a constant amplitude modulation system all the power amplifier can be operated in class c and that is very efficient.
1.2 MODULATION (ANALOG AND DIGITAL
Modulation is the systematic transformation of a carrier wave in accordance with the message signal. To a large extent the success of a communication system in any given mission depends on the modulation so much so that the type of modulation is a pivotal decision to system design. There are two basic types of modulating techniques the analog and digital modulation. Analogue modulation uses sinusoidal waveform as the carrier signal while digital modulation uses a discrete or pulse train as the carrier signal. Analogue modulation being a continuous process is obviously suited to signal that are continually varying with time. The carriers are at a frequency much higher modulating signal. The modulation process is thus characterized by frequency translation. Pulse modulation is discontinuous or discrete process in the sense that the pulses are present only at a certain interval of time. In the past, analogue modulation methods have been very largely exploited and still are because of the capital investment in existing systems and theirs basic simplify. The two most important methods of analogue modulation are amplitude modulation.
1.3 AMPLITUDE MODULATION (AM).
In amplitude modulation the amplitude of a carrier the modulating voltage whose frequency is invariably lower than that of the carrier varies signal. AM is defined as a system of modulation in which the amplitude of the carrier is made proportional to the instantaneous amplitude of the modulating voltage. Let the carrier voltage and the modulating voltage Vc and Vm respectively be represented by
Vc = VC Sin Wct
Vm = Vm Sin Wmt
Note that phase angle has been ignored in both expressions since it is unchanged by the amplitude modulation process from the definition of AIG amplitude vc. Of the unmodulated carrier will have to be made proportion to the instantaneous modulating voltage vm sin wmt where the carrier is amplitude modulated.
1.4 FREQUENCY MODULATION
Frequency modulation is a system in which the amplitude of the carrier is made constant whereas its frequency is varied about its unmodulated frequency in a way and manner determined by the amplitude of the modulating signal. When the information signal is positive the carrier frequency is increased above its unmodulated value. The increase in carrier frequency varies linearly with the instantaneous value of the information reaching a maximum when the modulating signal reaches its peak value. The converse applies when the modulating signals is negative ie the instantaneous carrier.
Frequency being decreased in proportion to the instantaneous value the modulating or information signal.
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