TechnicalBasics

Unlike other radio users radio amateurs are interested in how radio works and may eventually want to design and build their own equipment.

At foundation level most of the training is about using the radio but a basic understanding of electrical and magnetic concepts, symbols and units is introduced.

It is important to have a basic understanding of:Conductors and InsulatorsVoltage, Current, Power and Resistance and how they are relatedFrequency and Wavelength and how they are relatedBasic symbols and diagrams

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Introduction

But you don’t need to be a circuit designer.

Conductors and Insulators

Conductors permit the flow of electric currentExamples: Copper, Brass etc

Metallic conductors allow electrons to flow easily

Beware of poor or oxidized surfaces (eg on Aluminium, Steel)

Insulators don’t permit electron flow and exhibit high resistance. Examples: Plastics, wood, rubber, glass, ceramics

Note: water is a conductor (esp. when impure), andwet insulators can therefore conduct across their surfacesThis can be a risk when using outdoor/portable equipment

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Quantities, units and symbols

Quantity Unit SymbolVoltage (V) Volt VCurrent (I) Amp AResistance (R) Ohm ΩPower (P) Watt WFrequency (f) Hertz HzWavelength (λ) Metre m

Note 1: Resistance is the opposition to current flowNote 2: Voltage is sometimes referred to as Potential Difference

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Unit prefixes

Factor Prefix Symbolmillionths micro μor uthousandths milli mthousands kilo kmillions Mega M

4.7kΩ= 4700Ω1500mA = 1.5A0.6MHz = 600kHz500mW = 0.5W

Examples:

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Ohm's Law

Relationship of Voltage (V) to Current (I) and Resistance (R)V=IxR or I=V/R or R=V/I

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V

I R

Power relationships

Relationship of Power (P) to Voltage (V) and Current (I) P=VxI or V=P/I or I=P/V

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P

V I

Direct Current & Alternating Current

Is obtained from Cells or Batteries Direct Current (DC):

and only flows in one direction

Alternating Current (AC):Is easier to generate and transform. The mains supply is low frequency AC (50Hz).

Simple items such as Filament Light Bulbs work with AC and DC, but many electronic components are sensitive to the direction of current

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Radio Frequencies (RF) are high frequency AC.

It flows in alternating directions

Sound is also an alternating signal. Human hearing range is ≈ 100Hz - 15kHz

Frequency and wavelengthIn air the velocity of radio waves is a constant

and is determined by the formula: v = f x λIf the frequency increases, the wavelength decreases (and vice versa)

Don't worry, a 1MHz to 1000MHz conversion chart, and a frequency allocation table will be available for you to use in the exam.

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≈ 3x108m/s

v

λf

v

λwhere: v = velocity, f = frequency and λ = wavelength

Circuit diagram symbolsA few of the component symbols it is useful to recognise

microphone

fuse

cell

battery

resistor

lamp

earth

crystal

Switch (spst)

loudspeaker

aerial (antenna)

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clip art by OCAL

clip art by OCAL

clip art by OCAL

clip art by OCAL

clip art by Florian

Revision questions

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P

V I

I

V

Ohm

v

Power Velocity

λf

's Law

R

Twoof the

missingquantities

areV and P.Whichgoes

where?

What is the other missing quantity?

Triangleswork!