Table of Contents
Introduction
Electronics and radio are everywhere: phones, aircraft, cars, medical devices, and the ham radio repeaters I manage. To learn electronics, we start with components, then schematics, then circuits, and finally systems like radios and simulators.
Electronic Components
Resistors
Resistors limit current and divide voltages. The value is measured in ohms (Ω).
Formula: Ohm’s Law → V = I × R
Symbol: ---/\/\/\/---
Example: 1 kΩ (1000 ohms)
Applications:
- LED current limiting
- Voltage dividers
- Biasing transistors
// Voltage Divider
Vout = Vin × (R2 / (R1 + R2))
Capacitors
Capacitors store and release energy. They block DC but pass AC signals.
Formula: Q = C × V
Symbol: ---||---
Example: 100 µF electrolytic
Applications:
- Filtering in power supplies
- Coupling/decoupling AC signals
- Timing circuits (with resistors)
// RC Time Constant
τ = R × C
(time to reach 63% of final voltage)
Inductors
Inductors store energy in a magnetic field. They resist changes in current.
Formula: V = L × (dI/dt)
Symbol: ---coil---
Example: 10 µH choke
Applications:
- RF filters
- Switching power supplies
- Chokes to block interference
Diodes
Diodes allow current to flow in one direction. Voltage drop is typically ~0.7V for silicon.
Symbol: ---|>|---
Example: 1N4148 small-signal diode
Applications:
- Rectifiers (AC → DC)
- Protection (flyback diodes on relays)
- Signal detection in RF
Transistors
Transistors act as amplifiers or switches. Two main families: BJTs and MOSFETs.
Formula (BJT): Ic = β × Ib
Formula (MOSFET): Id ≈ k × (Vgs - Vth)²
NPN BJT Symbol:
C
|
|\
| >--- E
|/
B
Applications:
- Audio/RF amplification
- Logic gates
- Switching power loads
Integrated Circuits (ICs)
ICs are entire circuits in one package: op-amps, logic gates, microcontrollers.
Symbol: [ U1 ]
Example: 555 Timer IC, LM358 Op-Amp
Applications:
- Op-amps (signal conditioning)
- Microcontrollers (Arduino, ESP32)
- Radio transceivers (SDR chips)
Reading Schematics
A schematic is a map of a circuit. Learn the symbols, trace current flow, and spot subsystems.
Example LED Circuit:
+5V ---[ R1 330Ω ]---|>|--- GND
LED
Practice: take a circuit board, find the schematic, and trace from input to output.
Basic Circuits
RC Low-Pass Filter
Input ---R---+--- Output
|
C
GND
Filters out high-frequency noise. Used in audio, RF, and power supply design.
Transistor Amplifier
Input --C1--B Q1 C--- Output
E |
GND
Common-emitter amplifier boosts signals, crucial in radios.
Radio & RF Concepts
- Modulation: AM/FM for analog; QPSK, C4FM for digital.
- Impedance: Keep 50Ω match to avoid reflections.
- Repeaters: Extend coverage by retransmitting signals.
Antennas
Antennas are the bridge between electronics and RF waves.
- Dipole: Half-wave, classic ham antenna.
- Yagi: Directional, used in TV and ham beams.
- Vertical: Omni, good for repeaters.
- Phased Arrays: Steer beams electronically.
Troubleshooting
- Check power first.
- Check signal path with scope/meter.
- Compare to schematic expectations.
- Swap suspected parts with known-good.
Test Equipment
- Multimeter: Voltage, current, resistance.
- Oscilloscope: Waveforms in time domain.
- Spectrum Analyzer: Frequency analysis.
- VNA: Impedance and antenna matching.
- Service Monitor: All-in-one RF testing.
Project Examples
- Built and maintained linked ham repeaters.
- Developed DispatchLink for AI-driven scanner audio.
- Created Python SDR pipelines for OP25 trunking.
- Troubleshot avionics and simulators at component level.