THE DESIGN AND CONSTRUCTION OF MINI RADIO BROADCAST TRANSMITTER AND AUDIO CONSOLE USING FREQUENCY MODULATION (FM) WITH POWER RATING OF 1 WATT
ABSTRACT
The early radio transmitters were so large and bulky that they took up a lot of space. The circuits are primarily designed with large-sized valves.
With the introduction of semiconductor materials such as transistors, electronic equipment is being miniaturized to the point where small transmitters are becoming useful and compact.
As a result, we chose to design a complete radio broadcasting equipment that is compact and contains semiconductor materials.
The system units are divided into two types: An audio console for musical processing and mixing is essentially a condenser microphone.
The center frequency is provided by the transmitter unit. All of these were designed to be compact and small. This project is intended to help a specific group of people. Using a small and compact radio broadcasting equipment with a power watt of one watt, a community of one kilometer in radius should be covered comfortably, and the audio production should be very clear, as opposed to the common noisy FM microphone project.
CONTENTS TABLE
CHAPTER 1: TRANSMITTER FUNDAMENTALS AND MODULATION TYPES
1.1 The importance of transmitters
1.2 Modifications (analog and digital)
1.3 Modulation of amplitude
1.4 Modulation of frequency
1.5 The FM Method
1.6 Overview of Modulation
1.61 Modulator of basic reactance
1.62 Reactance modulator theory
1.70 Different types of reactance modulators
1.7.1 Modulator of varacto diodes
AMPLIFIER EXPLAINATIONS IN CHAPTER 2
2.10 An explanation of amplifiers
2.20 Classification of amplifiers
2.21 Classification of amplifiers
2.22 Power amplifier of Class B
2.23 Class AB power amplifier
2.24 Amplifier of Class C
Oscillators, 2.30
2.31 Different types of oscillators
CHAPITRE 3.0
LINE OF TRANSMISSION
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
design of a power supply
AUDIO CONSOLE UNIT (CHAPTER 5)
Transducer for 5.1 audio console
5.2 Pre-amp stage of an audio console
5.3 Power amplifier stage for audio console
5.4 Audio console/mixer control
5.5 How does the audio console work?
TRANSMITTER AND ANTENNA DESIGN (CHAPTER 6)
6.1 Oscillator stage design for a transmitter
6.2 Design of a buffer/power amplifier
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
power supply layout
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 Audio console operation
TRANSMITTER AND ANTENNA DESIGN
6.1 Transmitter Oscillator Stage Design
6.2 Buffer/power amplifier design
6.3 Tank circuit design
6.4 Antenna design
6.41 Antenna Types and Applications
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 Soldering Safety Precautions
7.5 Troubleshooting
7.6 Transmitter strip board
7.7 Audio console strip board
RECOMMENDATION
CONCLUSION
REFERENCE:
LIST OF FIGURES AND DIAGRAM
Figure 1.4 Information signal
Fig 1.62 Circuit of a reactance modulator
Fig 1.7
amp
Tank circuit (Fig. 6.3)
Antenna matching network (Figure 6.42).
Fig 7.1 LM 386 (power amp)
7.11 Capacitor diagram
Figure 7.12: A transistor
Quantity bill
Diagram of an audio console’s blocks
Diagram of the transmitter’s blocks
Audio console diagram
Schematic of a transmitter
Casing for the transmitter
Case for an audio console
INTRODUCTION
Our project work consists of designing and building a complete radio broadcasting equipment that is compact and miniaturized. It has a power output of 1 watt and is expected to cover a distance of 400 meters (200 meters radius depending on obstructions).
The transmitted signal is frequency modulated, and its frequency varies in response to amplitude variations in the audio signal. When the amplitude of the input signal increases (i.e. during the positive half cycle), the frequency of the carrier increases as well. When the amplitude of the input signal decreases (negative half-cycle or no signal), the frequency of the carrier decreases as well.
The transmitter’s output frequency can be adjusted from 88 to 108 MHZ. The FM band is used for radio broadcasting. As previously stated, the circuit is divided into four stages. For modulation, three RF stages and one audio preamplifier are used. The first RF stage, an oscillator, is controlled by the LC network L-C, C ensures that the circuit continues to oscillate, and C adjusts the coupling between the oscillator and the next RF stage, an amplifier. This is based on TR2, which operates in clas c and is tuned using L and C. The final RF stage is also an amplifier built around TR3 that operates in class c and has an input tuned by c and l. The output of this final stage, which is
The output signal is then tuned using l-c and sent to the aerial via the tune circuit l-c.
The preamplifier circuit is very simple and is based on TR4. The stage’s input sensitivity is adjustable in order to use the transmitter with different input signals, and it is determined by the VRI setting. Because of this, the transmitter can be modulated directly using a piezoelectric microphone, a small cassette recorder, or other devices. Of course, an audio mixer can be used 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 so much power that efficiency is essential. Amplitude modulation can be generated at any point after the radio frequency source; in fact, a crystal oscillator could be amplitude modulated, but this would interfere with its frequency stability. High-level modulation occurs when the output stage of a transmitter is plate modulated.
A stable RF source and buffer amplifier are followed by an RF power amplifier in an AM transmitter that can be either low level or high level modulated. The audio voltage is processed or filtered so that it occupies the correct bandwidth and is compressed to reduce the maximum to minimum amplitude ratio.
The primary requirement in an IM transmitter
A variable output frequency of an FM system is proportional to the instantaneous amplitude or modulation voltage.
The power and auxiliary stages of an FM transmitter are similar to those of an AM transmitter, with the exception that because FM is a constant amplitude modulation system, all of the power amplifiers can be operated in class c, which is very efficient.
MODULATION (ANALOG AND DIGITAL) 1.2
The systematic transformation of a carrier wave in accordance with the message signal is known as modulation. The success of a communication system in any given mission is heavily dependent on modulation, so the type of modulation is a critical decision in system design. Modulating can be classified into two types.
Modulation techniques include analog and digital modulation. The carrier signal in analog modulation is a sinusoidal waveform, whereas the carrier signal in digital modulation is a discrete or pulse train. Analogue modulation, as a continuous process, is clearly suited to signals that change over time. The carriers modulate the signal at a much higher frequency. Thus, frequency translation characterizes the modulation process. Pulse modulation is a discontinuous or discrete process in the sense that the pulses appear only at specific time intervals. Analogue modulation methods were and continue to be widely used in the past due to the capital investment in existing systems and their basic simplicity. The two most important methods of analogue modulation are amplitude modulation and phase modulation.
1.3 AMPLITUDE MODULATION (AM).
In amplitude modulation, the modulating voltage whose frequency is invariably lower than that of the carrier varies the signal. AM is defined as a modulation system in which the carrier amplitude is proportional to the instantaneous amplitude of the modulating voltage. Let Vc and Vm represent the carrier voltage and modulating voltage, respectively.
Vc = Wct Sin VC
Vm = Sin Wmt Vm
It is worth noting that the phase angle has been ignored in both expressions because it is unaffected by the amplitude modulation process from the definition of AIG amplitude vc. Where the carrier is amplitude modulated, the unmodulated carrier must be proportional to the instantaneous modulating voltage vm sin wmt.
1.4 MODULATION OF FREQUENCY
Frequency modulation is a system in which the carrier’s amplitude is held constant while its frequency varies about its unmodulated frequency in a way and manner determined by the modulating signal’s amplitude. The carrier frequency is increased above its unmodulated value when the information signal is positive. When the modulating signal reaches its maximum value, the increase in carrier frequency varies linearly with the instantaneous value of the information. When the modulating signal is negative, i.e. the instantaneous carrier, the converse holds true.
The modulating or information signal’s frequency is reduced in proportion to its instantaneous value.
The example is shown below.
Signal amplification
V
0 Fig 1.4a
The carrier signal
V
0 Fig 1.4b
V Frequency modulated signal
1.5 MODULATION OF FREQUENCY METHOD
There are two approaches: direct and indirect. The frequency of an oscillator is varied to produce frequency modulation in the direct method. FM of some form will result if the capacitance or inductance of a L C oscillator tank is varied, and true FM will be obtained if the variation is made directly proportional to the voltage supplied by the modulation circuits. The disadvantage of the direct modulator is that it is based on an LC oscillator, which is not stable enough for broadcast use.
True FM will be obtained if the variation is made directly proportional to the voltage supplied by the modulation circuits. The disadvantage of direct modulators is that they are based on an LV oscillator, which is inherently unstable.
Not stable enough for broadcasting. This necessitates modulator stabilization, which increases circuit complexity: this method is known as the INDIRECT METHOD.
1.6 OVERVIEW OF THE MODULATOR
The reactance modulator and vibratory diode are the most common methods of providing voltage variable reactions that can be connected across the tank circuits of an oscillator. These will now be discussed in the following order:
1.61 SIMPLE REACTANCE MODULATOR
If certain simple conditions are met, the impedance Z seen at the figure’s input terminals A-A is almost entirely reactive. The circuit shown is the basic circuit of FET reactance modulator which behaves as a three- terminal reactance that may be connected across the tank circuit of the oscillator to be frequency modulated. It can
A simple component swap can convert it to inductive or capacitive operation. The value of this reactance is proportional to the device’s Tran conductance, which can be made to vary with the gate bias.
1.62 REACTION MODULATOR THEORY
A voltage V is applied to the terminals A-A between which the impedance is to be measured in order to calculate Z, and the resulting current I is calculated.
When the applied voltage is divided by the current, the impedance seen when looking into the terminals is obtained. To be a pure reactance, this impedance must be a pure reactance (it is capacitive here). Two requirements must be met.
ib
Z
Vg
The fundamental reactance
The modulator circuit
The first is that the bias network current ib must
be insignificant in comparison to the drain current. The bias network’s impedance must be large enough to be ignored. The second requirement is that the drain-to-gate impedance (Xc in this case) be greater than the gate-to-source impedance (R), preferably by more than 5:1. The following analysis could then be used.
RV = ibR + Vg
R-jXc
The drain current of a FET is
I = gmRv + gmVg
R-jXc
:. Resistance at A – A
V = V – gmRv R – jXc Z = V = V
R-jXc gmR I R-jXc gmR
= I . (I jXc) (I jXc)
gm R
Z = -j Xc
gmR
Xeq = Xc = I I.
2P Fceq gmR 2P fgmRC
gmRc = Ceq
Xc = 1
Wc = nR
Ceq = gmRc Ceq = gmR
2Õ FnR
ceq = gm
2Õ Fn
1.7.1 REACTANCE MODULATOR TYPES
There are four distinct
The reactance modulator arrangement (including the one previously discussed) will yield useful results. Their information is shown in the table below. The general requirement for all of them is that the drain current be significantly greater than the bias network current. Two of the arrangements produced a capacitive reactance, while the other two produced an inductive reactance.
An RC capacitive transistor reactance modulator, which is quite common in use, is shown below. It operates on the tank circuit of a clap -Gouriet oscillator. With one exception, any reactance modulator may be connected across the tank circuit of any LC oscillator (not crystal) if the correct component values are used. It is not permissible to use an oscillator that requires
It uses two tuned circuits to operate, such as the tuned-base tuned-collector oscillator. The most common oscillators are the hartly and copitts (or clap-Gouriet) oscillators, which should be isolated with a buffer. In the circuit shown, RF chokes are used to isolate various points of the circuit from alternating current while still providing a direct current path.
TABLE 1.7 Elements of Reactance Modulators
Zgd Zgs Condition Reactance Formula A NAME
Capacitive RC
C
R
Xc> > R
gmRC = Ceq
Inductive RC
R
C
R> > Xc
Leq =RC
gm
Iductive RL
L
R
XL > >R
Leq = L
gmR
Capacitive RL
R
L
R> > XL
Ceq = milliliters
R
DIODE MODULATOR 1.8 VARACTOR
Cc
When a varactor diode is turned on, the junction capacitance varies linearly with the applied voltage. The diode is biased in the opposite direction. It can also generate frequency modulation. To provide automatic frequency correction for an FM transmitter, a varactor diode is frequently used in conjunction with a reactance modulator. The circuit below depicts one such modulator. The diode has been back biased to provide the junction capacitance effect, and because this bias is varied by the modulating voltage in series with it, the junction capacitance varies as well, causing the oscillator frequency to change accordingly. Despite the fact that this is the most basic reactance modulator circuit. It does have the disadvantage of using a two-terminal device, which limits its applications. It is, however, also used for automatic frequency control and remote turning.
To make an oscillator
AF Cb (Rf) in
Varactor
diode
Figure 1.8: Variactor diode modulator Vb
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