Technical Aspects
2ABasic Electrical Quantities
2A1: Voltage, Current, and Resistance
The three fundamental quantities in electronics are:
Voltage (V)
The "push" that moves electrons. Measured in Volts. Think of it as electrical pressure.
Current (I)
The flow of electrons. Measured in Amps. Think of it as the amount of electricity flowing.
Resistance (R)
Opposition to current flow. Measured in Ohms (Ω). Think of it as a narrowing in a pipe.
Ohm's Law
V = I × R
Voltage = Current × Resistance
2A2: Power Equations
Electrical power is the rate at which energy is used, measured in Watts (W).
P = V × I
Power = Voltage × Current
P = I² × R
Power = Current² × Resistance
P = V² / R
Power = Voltage² / Resistance
2A3: Resistors in Series and Parallel
Series
Rtotal = R₁ + R₂ + R₃ + ...
Resistances simply add up. Total resistance is always greater than the largest individual resistor.
Parallel
1/Rtotal = 1/R₁ + 1/R₂ + 1/R₃ + ...
Total resistance is always less than the smallest individual resistor.
2BEnergy in Resistors
2B1: Energy Transfer
When current flows through a resistor, electrical energy is converted into heat. This is called heat dissipation.
- The higher the resistance and current, the more heat is generated
- This is why components get warm during operation
- Power ratings of components must not be exceeded
2CCapacitors and Inductors
2C1: Capacitors
A capacitor stores energy in an electric field between two conductive plates separated by an insulator (dielectric).
- Measured in Farads (F) — usually microfarads (µF) or picofarads (pF)
- Blocks DC but passes AC
- Used for filtering, coupling, and timing circuits
2C2: Inductors
An inductor stores energy in a magnetic field created by current flowing through a coil of wire.
- Measured in Henrys (H) — usually millihenrys (mH) or microhenrys (µH)
- Passes DC but opposes changes in current
- Used in filters, oscillators, and power supplies
2C4: Reactance
Reactance is the opposition to alternating current offered by capacitors and inductors. Unlike resistance, reactance changes with frequency.
- Capacitive reactance decreases as frequency increases
- Inductive reactance increases as frequency increases
2DAC and DC
2D1: Direct Current (DC) vs Alternating Current (AC)
DC
Flows in one constant direction. Produced by batteries and DC power supplies.
AC
Periodically reverses direction. Mains electricity is AC. Radio signals are AC.
2D2: Frequency
Frequency is the number of complete cycles per second, measured in Hertz (Hz).
- 1 Hz = one cycle per second
- Kilohertz (kHz) = 1,000 Hz
- Megahertz (MHz) = 1,000,000 Hz
- Gigahertz (GHz) = 1,000,000,000 Hz
2D3: Period
Period (T) = 1 / Frequency (f)
The time for one complete cycle, measured in seconds.
2D4: RMS Values
RMS (Root Mean Square) is a way of expressing AC voltage or current as an equivalent DC value. It represents the effective value of an AC signal.
For a sinusoidal waveform: Vrms = Vpeak × 0.707
2D7: Resonance
Resonance occurs when a circuit's inductive and capacitive reactances are equal, causing the circuit to respond strongly at a particular frequency.
Series Resonance
- Impedance is at minimum
- Current is at maximum
- Used in radio tuning circuits
Parallel Resonance
- Impedance is at maximum
- Current is at minimum
- Used in filter and oscillator circuits
2EFilters
2E1: Types of Filters
Low-Pass
Passes frequencies below a cutoff point. Blocks higher frequencies.
High-Pass
Passes frequencies above a cutoff point. Blocks lower frequencies.
Band-Pass
Passes a range of frequencies. Blocks everything outside that range.
2E2: Filter Applications
- Low-pass filters — remove high-frequency noise, smooth audio signals
- High-pass filters — remove low-frequency hum (e.g., mains hum)
- Band-pass filters — select a specific range of frequencies (e.g., in a radio receiver)
2E7: Decibels (dB)
Decibels express the ratio between two values (power, voltage, or current) on a logarithmic scale.
| dB Change | Power Ratio | Meaning |
|---|---|---|
| +3 dB | ×2 | Double the power |
| -3 dB | ×0.5 | Half the power |
| +10 dB | ×10 | 10× the power |
| -10 dB | ×0.1 | Tenth of the power |
| +6 dB | ×4 | 4× the power |
2FDigital Signals
2F1: Analogue vs Digital
Analogue
- Continuous signal
- Can take any value within a range
- Example: voice on AM/FM radio
Digital
- Discrete signal (on/off)
- Represented as binary (0s and 1s)
- Example: PSK31, FT8, data modes
2F2: Binary and Sampling
- Binary uses two states: 0 and 1 (bits)
- A byte is 8 bits
- Sampling converts an analogue signal to digital by measuring it at regular intervals
- Higher sampling rates capture more detail
2GMicroprocessors
2G1: Basic Concepts
A microprocessor is a small computer on a single integrated circuit. It executes instructions stored in memory.
- Microprocessors are used in modern radio equipment for control and digital modes
- They follow a fetch-decode-execute cycle
- Software Defined Radios (SDRs) rely heavily on digital signal processing
2HCircuit Symbols
2H1-2H5: Standard Circuit Symbols
You should be able to recognise the standard symbols used in circuit diagrams:
| Symbol | Component | Description |
|---|---|---|
| —| |— | Capacitor | Two parallel lines (sometimes one curved) |
| —MMM— | Inductor | Series of bumps or loops |
| —/\/\/— | Resistor | Zigzag line |
| —▶|— | Diode | Triangle with bar (arrow points in direction of conventional current) |
| —GBT— | Transistor | Various types (NPN, PNP, FET) |
| —⊕— | Ground/Earth | Three horizontal lines of decreasing width |