basic electronics formulas
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PHYS 401 Physics of Ham Radio26
Basic Electronics
Chapter 2, 3ABasic Electrical Principles andthe Functions of Components
Figures in this course book arereproduced with the permission of the American Radio Relay League.
This booklet was compiled byJohn 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 similar to a 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 inamperes. (convention current sign is to electron velocity)
Resistance (ohms, ) is the ability to oppose an electricalcurrent.
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Circuit DefinitionsA circuit must close to be complete!
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Ohm
s Law Ohm
s 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 YoungGrass By Violets Growing Wild
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Resistor Types - Precision
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Resistors - Film Type
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Resistors VariablePotentiometers used for volume control
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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 (opposite to resistance) Capacitance is determined by 3 factors:
plate surface area plate spacing insulating material (dielectric)
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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 inElectric 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
(like resistors) 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 byelectrons whichflow 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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Meters - Measuring CurrentAmmetermust bepart of the
circuit tomeasurethe current
VOM -multimeterthatmeasures E,I, R
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Meters - Measuring VoltageVoltmeter
measuresacross thecircuit (inparallel tothe voltage
to bemeasured)
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Meters - Measuring ResistanceOhmmeter: measures across the resistor (but
be sure the circuit is not turned on
hot
).Puts in a known voltage and measures thecurrent, so it requires a battery. If the circuitis energized, will give the wrong reading!
Never leave a multimeter set at
ohms
- willrun 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 areconnected.
Block diagrams show
larger components(black boxes) and howthey 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 and
others 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.
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