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Technical Basics

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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 Insulators Voltage, Current, Power and Resistance and how they are related Frequency and Wavelength and how they are related Basic symbols and diagrams >> Introduction But you don’t need to be a circuit designer.

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Conductors and Insulators Conductors permit the flow of electric current Examples: 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), and wet insulators can therefore conduct across their surfaces This can be a risk when using outdoor/portable equipment >>

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Quantities, units and symbols QuantityUnitSymbol Voltage (V)VoltV Current (I)AmpA Resistance (R)OhmΩ Power (P)WattW Frequency (f)HertzHz Wavelength (λ)Metrem Note 1: Resistance is the opposition to current flow Note 2: Voltage is sometimes referred to as Potential Difference >>

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Unit prefixes FactorPrefixSymbol millionthsmicro μ or u thousandths millim thousandskilok millionsMegaM 4.7kΩ = 4700Ω 1500mA = 1.5A 0.6MHz = 600kHz 500mW = 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 >> V I R

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

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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 >> Radio Frequencies (RF) are high frequency AC. It flows in alternating directions Sound is also an alternating signal. Human hearing range is ≈ 100Hz - 15kHz

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Frequency and wavelength In air the velocity of radio waves is a constant and is determined by the formula: v = f x λ If 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. >> ≈ 3x10 8 m/s v λf v λ where: v = velocity, f = frequency and λ = wavelength

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Circuit diagram symbols A few of the component symbols it is useful to recognise microphone fuse cell battery resistor lamp earth crystal Switch (spst) loudspeaker aerial (antenna) >> clip art by OCAL clip art by Florian

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Revision questions >> P V I I V Ohm v Power Velocity λ f 's Law R Two of the missing quantities are V and P. Which goes where? What is the other missing quantity? Triangles work!

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