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PHYS 401 Physics of Ham Radio
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Basic Electronics
Chapter 2
Basic Electrical Principles and
the Functions of Components
Figures in this course book arereproduced with the permission of
the American Radio Relay League.
This booklet was compiled by
John P. Cross AB5OX
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Basic Electrical Principles Conductors - keep loose grip on their electrons and allow
electrons to move freely. Metals are usually goodconductors.
Insulators - keep close hold of their electrons and do notallow free movement of electrons. Glass, wood, plastic,mica, fiberglass and air are good insulators.
Electromotive Force (EMF) is the force that moveselectrons through conductors. Its unit of measure is theVolt. Think of it as pressure.
Voltage Source - has two terminals (+ and -). Someexamples are car batteries (12 volts DC), D cell batteries
(1.5 volts DC) and a wall socket (120 volts AC). Current - is the flow of electrons. It is measured in
amperes.
Resistance (ohms, ) is the ability to oppose an electricalcurrent.
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Circuit Definitions
A circuit must close to be complete!
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Ohms Law Ohms Law relates Current (I), Voltage (E) and Resistance
(R)
The relationship can be written three ways:
E = I x R I = E / R
R = E/I
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Resistors
Mnemonic: Black Bears Run On Young
Grass By Violets Growing Wild
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Resistor Types - Precision
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Resistors - Film Type
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Resistors - Variable
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Calculating Resistance
Series:
R=R1+R2+R3+R4(the voltage adds up)
Parallel:
1/R=1/R1+1/R2+1/R3(the current adds up)
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Capacitors Capacitors store energy in an electric field
Basic unit of capacitance is the farad (f)
Series: 1/C=1/C1+1/C2+1/C3
Parallel: C=C1+C2+C3
Capacitance is determined by 3 factors:
plate surface area plate spacing
insulating material (dielectric)
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PHYS 401 Physics of Ham Radio
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Variables Determining
Capacitance
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Parallel Capacitors Increase Plate
Area; increase charge so C
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Capacitors Store Energy in
Electric Field
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Variable Capacitors
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Inductors Inductors store energy in a magnetic field
(like a little electromagnet)
Basic unit of inductance is the henry (h) Parallel: 1/L=1/L1+1/L2+1/L3
Series: L=L1+L2+L3
Inductance is determined by 4 factors: number of turns
permeability of the core
cross sectional area of the core
spacing of the turns
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Variables Determining
Inductance
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Inductors Store Energy in
Magnetic Field
Current flow-->
Electron flow-->
Note: current
flows from + to -,
but is carried by
electrons which
flow from - to +
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Types of Inductors
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Power Power is the rate of energy consumption.
The basic unit of power is the watt (W)
Power can be calculated as follows:
P = I x E
Since E = I x R, you can also say:
P = I2 x R Since I = E / R, you can also say:
P = E2 / R
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PHYS 401 Physics of Ham Radio
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Meters - Measuring CurrentAmmeter
must be
part of the
circuit tomeasure
the current
VOM -multimeter
that
measures
E, I, R
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Meters - Measuring Voltage
Voltmeter
measuresacross the
circuit (in
parallel to
the voltageto be
measured)
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Meters - Measuring Resistance
Ohmmeter: measures across the resistor (but
be sure the circuit is not turned on hot).Puts in a known voltage and measures the
current, so it requires a battery. If the
circuit is energized, will give the wrong reading!
Never leave a multimeter set at ohms - will
run down its battery!
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Meters - Changing Range
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Schematic Symbol Examples
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Schematic and Block Diagrams Schematic diagrams
include all the
individual componentsand how they are
connected.
Block diagrams show
larger components(black boxes) and how
they are connected
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Amplifiers Tubes and transistors
amplify signals applied tobase or control grid.
Transistors haveadvantages:
size
power consumption
cooling
robustness Tubes have advantages:
high power
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Test Equipment Voltmeter - an instrument that is used to measure voltage.
It is used in parallel with a circuit to be measured.
a series resistor extends the range of the meter.
Ammeter - an instrument used to measure amperage in a circuit.
It is hooked up in series with the circuit to be tested.
A shunt resistor (in parallel w/meter) extends the range of the meter.
Multimeter - combines the functions above with resistance andothers to make a versatile piece of test equipment.
Wattmeter - a device that measures power coming from a
transmitter through the antenna feed line. A directionalwattmeter measures forward and reflected power. Wattmetersgenerally are useful in certain frequency ranges
Signal Generator - a device that produces a stable, adjustable lowlevel signal (AF or RF). It can be used to tune circuits.