MIRA Basic Amateur Radio Course

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MIRA Basic Amateur Radio Course

• Chapter 4 INDUCTORS AND CAPACITORS
• HC0400.ppt

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Review of Ch 3 Ohm's Law
Power Last time we showed you how current
behaves with various resistances and
voltages. We explained that there is more to
know than that which we have time to cover in
this course We looked at Ohm's Law with math
formulae We explained the term 'Power' in
electronics We asked you to practice what you
learned by answering a series of questions. Let's
look at them now....
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4.0 Introduction

• We use many resistors, capacitors and inductors
  as 'passive' circuit components
• Resistors place correct voltages at various
  points
• Capacitors pass AC signals well block DC
• Inductors ( coils ) pass DC block AC

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4.1 Inductors

• Generally, Coils
• Current through generates magnetic field
• Field depends upon - Number of turns
  - Coil size -
  Permeability of coil

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4.2 Inductance

• Temporarily stores energy as magnetic field
• Opposes any change of the field due to back EMF
• Unit is the Henry ( uH )
• Abbreviation is L
• Blocks AC but passes DC

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4.3 Inductance in Circuits

• Coil around air ( aircore ) or some permeable
  core
• Adjustable inductors
• Inductance varies with - Number
  of turns - Permeability of
  the core
• Measured in mH, uH, nH

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4.4 Inductance in Series

• Connecting inductance in series acts as a longer
  inductor so they add
• Lt L1 L2
• 2
  3 5 uH
• Formula works for any number of series inductors

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4.4 Inductance in Parallel

• Connecting inductance in parallel acts as a
  shorter inductor, so
• 1 1 1
  1 ---
  --- --- --- .
• Lt L1 L2 L
• Similar to resistors in parallel formula
• Formula ok for any number of parallel inductors

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4.5 Transformers Special Application of
Inductance
Used to change values of voltage and current
impedance Ep turns primary ----
---------------- Es turns secondary
(or) Ep Tp ----
---- Es Ts For example ....
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Calculate the number of turns on the secondary
windng of a transformer if the secondary voltage
is to be 20 vac while the primary is 120 vac
where primary turns 200 Step 1 Select a
formula Ep Tp Tp Es
---- ---- or Ts ---------- Es
Ts Ep (rationale) 2
6 6 9 --- --- or 27
------- 9 27 2
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Calculate the number of turns on the secondary
winding of a transformer if the secondary voltage
is to be 20 vac while the primary is 120 vac
where primary turns 200 Step 2 Substitute
values Tp Es 200 20
Ts -------- or Ts ---------- Ep
120 Step 3 Calculate
answer Ts
33.33333 Turns Step 4 Select the closest to
right answer on quiz form
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4.6 Capacitors and Capacitance

• Capacitors are 'temporary' storage reservoirs for
  electrons
• Made of 2 metallic plates separated by a
  'dielectric'
• Many different styles and materials used

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4.7 Factors affecting Capacitance

• Capacitance depends upon
• - Area of plates
• - Distance between plates
• - Dielectric
• Capacitance is measured in uF or pF

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4.8 Formulae for Capacitors in Series and
Parallel ( Note similarity to
resistor formulae )
Parallel
Capacitance Ct C1 C2 C3 ....
1 1
1 1 Series Capacitance --- ---
--- --- ...
Ct C1 C2 C3
1
Ct --------------------------
1 1 1
--- --- ---
... C1 C2
C3
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4.9 Working Voltage

• The voltage a capacitor can tolerate depends upon
  spacing of the plates and the dielectric used
  between the plates.

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4.10 Reactance - AC Meets Inductance or
Capacitance

• - Opposition to flow of AC, No effect on DC (
  AC Resistance! )
• - No energy dissipated, energy is stored and
  returned to circuit
• - Symbols
• - - - Capacitive Reactance symbol is ... Xc
• - - - Inductive Reactance symbol is ... Xl

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4.11 Inductive Reactance Xl

• Formula is Xl 2 pi f L
• Where Xl Inductive reactance in ohms
• pi 3.14
• f frequency in hertz
• L Inductance in H
• This formula shows that
• - - Reactance increases with Frequency
• - - Reactance increases with Inductance
  

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4.12 Capacitive Reactance Xc

• 1
• Xc
  -----------------
• 2 pi f
  C
• Where Xc Inductive reactance in ohms
• pi 3.14
• f frequency in hertz
• C Capacitance in Farads
• This formula shows that
• - - Reactance decreases with Frequency
• - - Reactance decreases with Capacitance

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4.13 Impedance

• Combination of Reactance and Resistance
• - Stated in Ohms, Symbol is Z
• 
  --------------
• - Formula is Z
  / R2 X2
• 
  \-/
• - Important in Impedance Matching
• affecting efficiency of power
  transfer
• Zs N2 sec
• ----
  ---------
• Zp N2 pri

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4.14 Resonance

• Xl Xc which cancel one another ( at one
  frequency only)
• - Series Resonance - minimum Impedance
• - Parallel Resonance - maximum Impedance . . . .
  

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4.15 Tuned Circuits

• - Resonant circuits transfer power efficiently at
  one frequency.
• - Important because hams are trying to select a
  particular frequency from the millions available
• - Q - A measure of the efficiency of a resonant
  circuit.

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1.3 Internet Resources Useful Links

• Overview Radio Amateurs of Canada Homepage
• Overview American Radio Relay League
• Online Course ARES Ontario Basic Online Course
• Hamstudy.com - fee based online course
• Scott's guide to Electronics - an excellent
  online reference
• A 'kitchen table' Experimental approach to
  Electronics
• Java Appletes Simulated Electronic Circuits
• Australian -Electronics Tutorials
• Industry Canada Exam Generator
• Use your favourite search engine to find
  additional sites ( 'tutorial' 'electronics' etc )

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Chapter 4 INDUCTORS AND CAPACITORS 4.1
Inductors 4.2 Inductance 4.3 Inductance in
Circuits 4.4 Inductance in Series and Parellel
4.5 Transformers - Specia Application of
Inductance 4.6 Capacitors and Capacitance 4.7
Factors affecting Capacitance 4.8 Capacitors in
Series and parallel 4.9 Working Voltage 4.10
Reactance - AC Meets Inductance or Capacitance
4.11 Inductive Reactance Xl 4.12 Capacitive
Reactance Xc 4.13 Impedance 4.14 Resonance
4.15 Tuned Circuits