Currents & Concepts
These components are the heart of modern electronics and radio circuits:
Diodes steer current and protect circuits.
Transistors act as switches or amplifiers.
Amplifiers make weak signals strong enough to be heard or transmitted.
Without these, your transceiver would be just a bunch of inert parts.
Diodes – The One-Way Valves of Electricity
What They Do:
A diode allows current to flow in only one direction, like a one-way valve in plumbing.
Symbol:
—►|—
(anode → cathode)
Behavior:
|
Condition |
Behavior
|
|---|---|
| Forward-biased |
Conducts current
|
| Reverse-biased |
Blocks current
|
Applications in Ham Radio:
Rectification: Converting AC into DC in power supplies.
Reverse-polarity protection: Prevents damage if power is connected backward.
Signal detection: Extracts audio from AM signals in simple receivers.
Switching & clamping: Used in RF switching and voltage spike suppression.
Special Diode Types:
|
Type |
Use Case
|
|---|---|
| Zener |
Voltage regulation
|
| Schottky |
Fast switching, low voltage drop (great for RF)current
|
| LED |
Light indication (voltage drop used too)
|
| Varicap |
Voltage-controlled capacitance — used in tuning circuits
|
Transistors – Tiny Switches and Signal Amplifiers
Types:
|
Type |
Description
|
|---|---|
| BJT |
Bipolar Junction Transistor – current-controlled
|
| FET |
Field Effect Transistor – voltage-controlled
|
BJT Terminals:
Base (control)
Collector (input)
Emitter (output)
Small current at the base controls large current between collector and emitter.
Modes of Operation:
|
Mode |
Description
|
|---|---|
| Cutoff |
Off (no current flows)
|
| Saturation |
Fully on (like a closed switch)
|
| Active region |
Amplification occurs
|
Applications in Ham Radio:
Oscillators: Generate RF carrier waves.
Amplifiers: Increase signal strength (audio or RF).
Mixers: Combine signals to change frequencies.
Switching: For relays, protection, or signal routing.
Amplifiers – Making Small Signals Big
What They Do:
An amplifier uses transistors (or tubes) to take a small input signal and produce a larger output signal that retains the original waveform’s shape.
Think:
A whisper turned into a shout
A weak radio signal boosted for transmission or audibility
Amplifier Types:
|
Type |
Description & Use
|
|---|---|
| Audio amplifier |
Boosts microphone signals or received audio
|
| RF amplifier |
Boosts RF signal before transmission or reception
|
| Power amplifier |
Final stage before transmission – high power output
|
| Linear amplifier |
Preserves waveform (used in SSB, AM)
|
| Class C amp |
Highly efficient, distorts signal (used in CW/FM)
|
Modes of Operation:
|
Class |
Linear?
|
Efficient? |
Common Use
|
|---|---|---|---|
| A |
Yes
|
Low |
Audio, clean RF
|
| AB |
Mostly
|
Medium |
RF amplifiers
|
| B |
No
|
Medium |
Push-pull amps
|
| C |
No
|
High |
Morse, FM only
|
For SSB and AM: linearity is crucial (Class A or AB).
For CW or FM: distortion doesn't matter (Class C = fine).
Thought Experiment
Imagine a water system:
A diode is a one-way valve.
A transistor is a controlled faucet — open it slightly or fully.
An amplifier is a powered pump — boosting pressure (voltage) or flow (current) without changing the water itself (signal shape).
Real-World Ham Radio Examples
|
Component |
Use Case
|
|---|---|
| Diode in power supply |
Rectifies AC into DC for your radio
|
| Transistor oscillator |
Creates carrier wave for transmission
|
| Microphone amplifier |
Boosts your voice before modulation
|
| Final RF amplifier |
Pushes signal from milliwatts to 100+ watts
|
| Protection diodes |
Save gear from reverse polarity or voltage spikes
|
summary
|
Component |
Function
|
Ham Radio Role
|
|---|---|---|
| Diode |
One-way current flow, rectification
|
Power conversion, signal detection, protection
|
| Transistor |
Controlled switch or amplifier
|
Oscillation, switching, amplification
|
| Amplifier |
Increases signal strength
|
Audio boost, RF transmission, final stage amps
|
Optional Visuals
Would you like:
A diagram of a transistor amplifier circuit?
A step-by-step animation of signal flow through a class AB RF amp?
A comparison chart of amplifier classes with waveform illustrations?