DESIGN AND FABRICATION OF DIP METER
This work is on dip meter. Dip meter is a measuring instrument to measure resonant frequency of radio frequency circuits. It is an oscillator whose amplitude changes when near a resonant circuit which is tuned to the frequency the oscillator generates. This is the main part of the instrument ( many different configurations are used in practice) is a very basic Colpits RF Oscillator using a VHF/UHF transistor. The meter uses a calibrated, tunable FET oscillator. It has a frequency range of 1,6 to 35,2 MHz in four ranges using a set of plug-in coils. When the oscillator coil, L1, is placed near an external resonant circuit, some of its RF energy is coupled into the external circuit. A gain in energy of the external circuit must mean a loss of energy in the circuit, resulting in a change of current through FET, which is measured by the meter, M1.
TABLE OF CONTENTS
TITLE PAGE
APPROVAL PAGE
DEDICATION
ACKNOWELDGEMENT
ABSTRACT
TABLE OF CONTENT
CHAPTER ONE
- INTRODUCTION
- BACKGROUND OF THE PROJECT
- AIM OF THE PROJECT
- ADVANTAGES OF THE PROJECT
- LIMITATION OF THE PROJECT
- PROBLEMS OF THE PROJECT
- APPLICATION OF THE PROJECT
- DEFINITION OF TERMS
CHAPTER TWO
2.0 LITERATURE REVIEW
2.1 HISTORICAL BACKGROUND OF THE STUDY
2.2 OVERVIEW OF VARIABLE-FREQUENCY OSCILLATOR
2.3 TYPES VARIABLE FREQUENCY OSCILLATOR
2.4 REVIEW OF VARIABLE CAPACITOR
2.5 MECHANICALLY CONTROLLED CAPACITANCE
2.6 REVIEW OF AN AMMETER
2.7 TYPES OF AMMETER
CHAPTER THREE
3.1 INTRODUCTION
3.3 SYSTEM OPERATION
3.4 CIRCUIT DIAGRAM OF SYSTEM
3.5 SYSTEM CIRCUIT DESCRIPTION
3.6 DESCRIPTION OF MAJOR COMPONENTS USED
CHAPTER FOUR
RESULT ANALYSIS
4.0 CONSTRUCTION PROCEDURE AND TESTING
4.1 CASING AND PACKAGING
4.2 ASSEMBLING OF SECTIONS
4.3 PACKAGING
4.4 MOUNTING PROCEDURE
4.5 TESTING
4.6 RESULT OF SYSTEM
4.7 COST ANALYSIS
CHAPTER FIVE
5.1 CONCLUSION
5.2 RECOMMENDATION
5.3 REFERENCES
CHAPTER ONE
1.0 INTRODUCTION
Dip meter is a measuring instrument to measure resonant frequency of radio frequency circuits. It measures the amount of absorption of a high frequency inductively coupled magnetic field by nearby objects. It is an oscillator whose amplitude changes when near a resonant circuit which is tuned to the frequency the oscillator generates. At the heart of the instrument is a tunable LC circuit with a coil that serves as a loose inductive coupling to the measured LC resonant circuit. Resonance is indicated by a dip in the meter indicator on the device, usually based on a microammeter.
A dip meter is nothing more than an oscillator with the frequency-determining coil exposed, so that it may be coupled to other electrical circuits. A frequency control is included so the oscillator’s approximate frequency is known and can be adjusted.
A meter indicates the level of oscillation. Most dip meters come with a set of plug-in coils for wide frequency coverage in several ranges. Older vacuum tube units, in which the meter monitored the grid current of the tube to indicate the level of oscillation, were called grid dip meters. With the availability of high frequency transistors, dip meters went high-tech and battery operation became practical.
The typical dip meter is contained in a small case, with provisions for external plug-in coils. A dial to control the oscillator frequency will be conveniently located on the unit. The meter is located for easy reading while the frequency is being adjusted. Most dippers will also have a control to adjust the level of oscillator activity. This control allows the operator to keep the meter indication at a convenient level over a wide frequency range. If it is a solid-state unit, a battery is included in the case, while vacuum tube units will have an ac power supply that may be self-contained or separate.
Sometimes there is a switch to kill the oscillator to facilitate its use as an absorption wave meter. On others it is possible to turn the activity control down far enough to stop the oscillator.
On the front panel there may be an audio output to listen to the modulation of a carrier.
1.1 AIM OF THE PROJECT
The main aim of this work is to built a device used to determine the resonant frequency of a circuit. They can be used to determine the inductance of a coil, the capacity of a capacitor, the resonant frequency of an antenna.
1.2 ADVANTAGES OF THE PROJECT
- Simplicity: therefore the GDO circuit is simple and costs are relatively low.
- Versatility: The dip meter is a versatile instrument that can be used in a variety of ways to provide several measurements.
- Low cost: The dip meter / grid dip oscillator has a very much lower cost than other RF instruments and therefore is within the financial reach of many radio amateurs and enthusiasts.
- Does not require a direct connection: The dip meter only requires its coil to be placed close to the coil or tuned circuit that is being tested. No direct connection is needed. This makes it very convenient to use.
1.3 LIMITATION OF THE PROJECT
- Inaccuracy: Simplicity - therefore the dip meter / GDO is very inaccurate.
- Free running oscillator: The grid dip oscillator or dip meter uses a free running oscillator and therefore this is subject to all the tolerances of this type of circuit. It is not able to offer the digital accuracy of many of today's items of radio equipment.
- Coupling: Coupling the tuned circuit of the oscillator within the GDO to an external circuit means that the oscillator circuit is 'pulled' by the external circuit and this leads to even more inaccuracy.
1.4 PROBLEMS OF THE PROJECT
Some of the grid dip meter issues include:
- Dip does not reduce as coils moved apart: In some instances it may be that as the coils are moved apart the dip on the grid dip meter does not reduce. This can occur for a number of reasons. The main one is that it is a dip that occurs within the dip meter itself. If this is the case, then it is necessary to find the real dip elsewhere. Alternatively if the dip is expected in the region of the false dip, then another coil with an overlapping range may be used.
- No dip is found: If no dip is found and there is sufficient coupling between the grid dip meter and the circuit under test then the resonance point must be outside the range of the coil being used on the meter. In this case another coil / range should be used. It is also necessary to check that there is sufficient coupling between the two circuits.
Normally measurements can be made quite easily and no issues are found. However when they do occur, they are normally overcome relatively easily.
1.5 APPLICATION OF THE PROJECT
Dip meter have been widely used by amateur radio operators for measuring the properties of resonant circuits, filters, and antennas.
1.6 DEFINITION OF TERMS
VFO – variable frequency oscillator
GDO - grid dip meter
LCC – inductor capacitor circuit
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