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Technical Basics

Technical Basics. Introduction. Unlike other radio users radio amateurs are interested in how radio works and may eventually want to design and build their own equipment. But you don’t need to be a circuit designer.

jana-barlow
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Technical Basics

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  1. Technical Basics

  2. Introduction Unlike other radio users radio amateurs are interested in how radio works andmay eventually want to design and build their own equipment. But you don’t need to be a circuit designer. 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 <<<===>>>

  3. 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), andwet insulators can therefore conduct across their surfaces This can be a risk when using outdoor/portable equipment <<<===>>>

  4. 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 <<<===>>>

  5. Unit prefixes FactorPrefixSymbol millionths micro μor u thousandths milli m thousands kilo k millions Mega M Examples: 4.7kΩ= 4700Ω 1500mA = 1.5A 0.6MHz = 600kHz 500mW = 0.5W <<<===>>>

  6. Ohm's Law V I R Relationship of Voltage (V) to Current (I) and Resistance (R) V=IxR or I=V/R or R=V/I <<<===>>>

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

  8. Direct Current & Alternating Current Direct Current (DC): Is obtained from Cells or Batteries and only flows in one direction Alternating Current (AC): Is easier to generate and transform. It flows in alternating directions The mains supply is low frequency AC (50Hz). Human hearing range is ≈ 100Hz - 15kHz Sound is also an alternating signal. Radio Frequencies (RF) are high frequency AC. Simple items such as Filament Light Bulbs work with AC and DC, but many electronic components are sensitive to the direction of current <<<===>>>

  9. Frequency and wavelength In air the velocity of radio waves is a constant ≈ 3x108m/s If the frequency increases, the wavelength decreases (and vice versa) and is determined by the formula: v = f x λ v v f λ λ where: v = velocity, f = frequency and λ = wavelength Don't worry, a 1MHz to 1000MHz conversion chart, and a frequency allocation table will be available for you to use in the exam. <<<===>>>

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

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

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