Electricity and electronics
The electrical engineering behind every radio: circuits, components, measurement and building.
Electrical basics
The quantities and laws every circuit obeys.
Voltage, current and resistanceThe three quantities every circuit is about.Ohm's lawThe relationship that links them, and how to use it.Power and energyWatts, joules and kilowatt-hours; P = E × I.AC, DC and waveformsSine, square and triangle; peak, peak-to-peak and RMS.Series and parallel circuitsHow resistors combine and where current and voltage divide.Kirchhoff's lawsCurrent in equals current out; voltages around a loop sum to zero.Units and metric prefixesFrom pico to giga, and converting without mistakes.Conductors and insulatorsWhy materials differ in how they carry current.
Reactance and AC theory
What capacitors and inductors do once the signal alternates.
CapacitanceStoring energy in an electric field.InductanceStoring energy in a magnetic field.Reactance and impedanceHow capacitors and inductors resist AC, and combine with resistance.Phasors and complex numbersThe maths that makes AC circuits tractable.Time constantsHow quickly RC and RL circuits charge and decay.Resonance and QTuned circuits, bandwidth and selectivity.TransformersTurns ratio, voltage, current and impedance transformation.Skin effect and RF resistanceWhy current crowds to the surface at high frequency.
Components
The parts, what they do, and how to choose them.
ResistorsTypes, ratings, tolerance and the colour code.CapacitorsCeramic, electrolytic, film and variable: choosing the right one.Inductors, toroids and ferritesCores, permeability, and why ferrite beads matter.Crystals and resonatorsPiezoelectric frequency references and filters.Switches, relays and fusesControlling and protecting circuits.BatteriesChemistries, capacity, internal resistance and charging.Wire, cable and gaugeAWG, current ratings, and where each wire type belongs.
Semiconductors
Diodes, transistors and the devices built from them.
Semiconductor basicsDoping, P-N junctions and how they conduct.DiodesRectifier, zener, Schottky, varactor, PIN and LED.Bipolar transistorsA small base current controlling a big collector current.FETs and MOSFETsVoltage-controlled devices for switching and RF.Integrated circuitsAnalog, digital and RF chips.Operational amplifiersThe building block of gain, filters and comparators.OptoelectronicsLEDs, photodiodes, solar cells and optoisolators.Vacuum tubesTriodes to beam tetrodes, and why they still power amplifiers.
Analog circuits
The functional blocks radios are assembled from.
Amplifiers and classes of operationGain, linearity and efficiency: classes A to C.OscillatorsAmplifier plus feedback: LC, crystal and VFO.FiltersLow-pass, high-pass, band-pass and notch; passive and active.Mixers and frequency conversionMaking sum and difference frequencies.Detectors and demodulatorsRecovering the audio from AM, FM and SSB.PLLs and frequency synthesizersLocking a variable oscillator to a stable reference.Power supplies and regulatorsTransformer, rectifier, filter, regulator; linear versus switching.Impedance matching networksL, Pi and T networks and how they transform impedance.Attenuators and padsReducing signal level without upsetting the impedance.
Digital electronics and DSP
Logic, conversion and signal processing.
Logic gatesAND, OR, NOT, NAND, NOR and XOR.Flip-flops, counters and shift registersMemory and sequencing in digital circuits.ADCs and DACsConverting between analog voltages and numbers.Digital signal processingFiltering and demodulating with maths instead of components.MicrocontrollersArduino, Pico and friends in the ham shack.
Measurement and test
Seeing what a circuit or antenna is really doing.
MultimetersMeasuring volts, amps and ohms safely.OscilloscopesSeeing voltage against time.Spectrum analyzersSeeing signal strength against frequency.SWR and power metersChecking forward and reflected power.Antenna analyzers and VNAsMeasuring impedance, SWR and resonance across a band.Dummy loadsTesting a transmitter without radiating.Frequency counters and signal generatorsMeasuring and creating test signals.
Building and workshop skills
Turning a schematic into a working circuit.