Chelmsford Amateur Radio Society Intermediate Course (3) Technical Basics - 1 Components

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Chelmsford Amateur Radio Society Intermediate
Course(3) Technical Basics - 1Components
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Electronic Components

• Nature Amateur Radio applies Electronics to
  Wireless Communication
• Items Common Electronic Components Include
• Resistors, inc Colour code
• Capacitors, Inductors, Resonant Circuits
• Diodes LEDs
• Transistors
• Switches, Fuses, Connectors
• The Intermediate Licence expects you to be able
  to recognise components, their circuit symbols,
  and to build and test simple circuits

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Insulators, Conductors Semiconductors

• Conductors permit the flow of electric current
• Examples Copper, Brass etc - (ie mainly metals)
• Metallic Conductors permit electrons to flow
  easily, but beware of poor/oxidised connections
  (eg on Aluminium, Steel)
• Insulators dont permit electron flow and exhibit
  high resistance.
• Examples Plastics, wood, rubber, glass, ceramics
• Water may conduct (esp. when impure) and that wet
  insulators therefore may conduct on their surface
  - a risk for outdoor work
• Semiconductors (Silicon, Germanium etc) barely
  conduct unless small dopants are added to create
  P or N-type materials

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Electrical Units

• Quantity Unit Symbol
• Voltage, V Volt V aka Potential Difference
• Current, I Amp A
• Resistance, R Ohm ?
• Capacitance Farad F
• Inductance Henry H
• Power, P Watt W
• Frequency, f Hertz Hz
• Wavelength, ? Metre m

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Unit Prefixes

• Factor SN Prefix Symbol
• trillionths 10-12 pico p
• billionths 10-9 nano n
• millionths 10-6 micro ? or u
• thousandths 10-3 milli m
• thousands 103 kilo k
• millions 106 Mega M
• billions 109 Giga G
• Examples 25kV 25000V 1500mA 1.5A
• 0.1uH 100nH 2.45GHz 2450MHz
• 10pF 0.01nF 0.5W 500mW

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Power
Recall from Foundation

• Relates Power, P Voltage, V Current, I
• PVxI VP/I IP/V

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Ohms Law
NB Take care when quantities in formulas use
unit prefixes

• Relates Voltage, V Current, I Resistance, R
• VIxR IV/R RV/I

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Cells Batteries

• Batteries provide a source of DC power
• Note symbols for Single Cells or Battery Packs
• Cells store electrical energy by chemical means
• Primary Cells can only be used once.
• Secondary cells can be recharged. This reverses
  the chemical reaction eg in Lead Acid, NiCd, LiMH
• Beware of Leakage, Shorts esp on Lead-Acid
• Dispose of carefully

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Resistors

• Fixed Resistors traditionally identified by
  Colour Code for Value Tolerance
• Note that the modern BSI Symbol is preferred to
  the zigzag

• Note all the symbols opposite for the various
  forms
• Check Wattage Rating

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Resistor Colour Code

• First two Bands give Value Digits
• Third Band is the Multiplier for Factor of Ten
• Fourth Band is Tolerance
• Example-

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Resistors in Series/Parallel

• Resistors in Series-
• Rtotal R1 R2 R3 . . .

• Resistors in Parallel-
• 1/Rtotal 1/R11/R21/R3 . . .
• For Identical Resistors this simplifies to...
• For Two Resistors Rtotal R/2
• For Three Resistors Rtotal R/3

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Inductors Transformers

• Inductors are Coils of Wire which may have air or
  ferrite/iron cores
• Energy is stored in the magnetic field
• Inductance is proportional to number of turns,
  diameter, core etc
• Inductance is in Henries eg mH, nH, pH
• Inductors pass DC but increasingly block AC at
  higher frequencies
• Pairs of coils can be used to create Transformers
  for PSUs, RF circuits etc

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Capacitors

• Capacitors are insulated plates, which can store
  electric charge and energy in the electric field
• Larger plate areas, the nature of materials
  between the plates or smaller plate separation
  will give higher capacitance
• Capacitance is in Farads eg uF, nF, pF
• Capacitors block DC but increasingly pass AC at
  higher frequencies
• Beware Voltage rating and polarity of
  Tantalum/Electrolytic versions
• Note all the symbols opposite

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Diodes

• Diodes are PN Junctions of semiconductor
  materials which only pass current one way
• Diodes are a key item in PSUs where they rectify
  AC into DC
• Note Forward Current and Reverse Voltage ratings,
  and a small forward bias Voltage Drop
• LEDs - Light Emitting Diodes
• Variable Capacitance Diodes exploits PN
  Junction Capacitance when reverse biased
• Zener Diodes - have a precise Reverse Voltage

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Transistors

• Bipolar Transistors are NPN or PNP junctions of
  semiconductor material
• Middle section is the Base. A small bias
  current can control a larger flow between
  Collector and Emitter
• In FET devices current flow between Drain and
  Source is controlled Electrostatically by the
  Gate voltage
• Depending on the circuit, Transistors can Amplify
  or Switch - or Oscillate
• Integrated Circuits have arrays of many
  Transistors on a single chip

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Transistor Gain

• Current flow in the Collector (IC) to the Emitter
  can be controlled by a smaller bias current in
  the Base, IB
• If levels are set correctly, small variations in
  base current are amplified at the output
• Current Gain or Beta is the ratio of IC/IB
• ß IC / IB
• or, IC ß x IB
• For example, a base current of 5mA in a device
  with Beta50 controls an IC of 0.25A

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Miscellaneous

• Also need to recognise symbols for Switches,
  Grounds, Crystals etc, etc

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Practicals

• Recognise Resistors by Colour Code
• Measure Resistors in Series
• Measure Resistors in Parallel
• Learn to Recognise other Components
• Soldering - correctly without damage
• Build and test board with resistors and transistor