Currents & Concepts
Many beginners think of electricity as one thing: voltage pushes current through a wire. That’s true for DC, but not the full picture for ham radio.
DC powers your radio.
AC is how your signal moves through circuits, oscillates in antennas, and travels through the air.
Understanding the differences between AC and DC is essential for grasping radio waves, tuning, and signal behavior.
What Is DC (Direct Current)?
Definition:
Direct Current (DC) is a one-directional flow of electric charge — constant in magnitude and direction.
Characteristics:
Voltage is steady over time
Current flows in one direction
Produced by batteries, DC power supplies, solar panels
Graph:
A flat, horizontal line when graphed against time
Applications:
Powering radios, microcontrollers, and digital circuits
Biasing transistors in amplifiers
Used internally in most electronics
What Is AC (Alternating Current)?
Definition:
Alternating Current (AC) is electricity where voltage and current periodically reverse direction — usually in a sine wave.
Characteristics:
Cycles between positive and negative voltage
Frequency is measured in Hertz (Hz) — 1 cycle per second
In RF, frequencies range from kHz to GHz
Household AC: 60 Hz in the US, 230V RMS at 50 Hz in most of the world
Graph:
A sine wave (smooth oscillation), though other shapes (square, triangle, etc.) exist in digital/RF systems
comparison table:
|
Feature |
DC |
AC
|
|---|---|---|
| Flow Direction | One direction |
Alternates (positive ↔ negative)
|
| Voltage Level | Constant |
Changes with time
|
| Source Example | Battery |
Wall outlet, RF oscillator
|
| Uses in Ham Radio | Powering gear |
Signal transmission, filtering, tuning
|
| Graph Shape | Flat line |
Sine wave (or other periodic shape)
|
Why AC Is the Language of Radio
Radio Signals = AC at High Frequencies
Radios transmit and receive AC signals — just at much higher frequencies than household power:
7 MHz for 40 meters
146 MHz for 2 meters
2.4 GHz for WiFi
These signals oscillate rapidly, carrying audio, data, and video.
A microphone converts your voice into an AC waveform
Your transmitter modulates that wave (AM, FM, SSB, etc.)
The antenna radiates it as alternating electromagnetic fields
Converting Between AC and DC
DC from AC: Rectifiers & Power Supplies
Wall outlets provide AC
Radios need DC
A power supply converts AC to DC using diodes, filters, and regulators
AC from DC: Oscillators & Inverters
In a transmitter, DC is converted into high-frequency AC signals
Oscillators produce steady sine waves
Modulation circuits imprint voice or data
Thought Experiment
Imagine a water pump pushing water through a pipe:
DC is like a pump pushing water in one direction — smooth, continuous flow.
AC is like a pump that reverses direction 60 times per second — the water sloshes back and forth.
If you connected a speaker to DC, it would “pop” once and then sit still. But with AC, it vibrates back and forth, producing sound — the same way radio waves vibrate the electromagnetic field to carry information.
Real-World Ham Radio Connections
|
Concept or Component |
Involves AC, DC, or Both? |
Why It Matters
|
|---|---|---|
| Transceiver power input | DC |
Radios expect stable 12–13.8V DC
|
| Antenna system | AC |
Radio waves are high-frequency AC signals
|
| Audio signals | AC |
Audio = low-frequency alternating current
|
| Filters & tuners | AC |
Only meaningful when current is changing
|
| Biasing transistors | DC |
Sets operating conditions for amplification
|
| Modulators/oscillators | DC → AC |
Generates RF signals from DC power
|
Summary
DC: steady, directional current — used to power electronics
AC: oscillating current — used to carry and process signals
Ham radio lives at the intersection — using DC to generate and control high-frequency AC
Optional Add-ons
Would you like:
A dual graph showing AC vs DC voltage over time?
An animation of AC current through an antenna?
A circuit simulation of a power supply converting AC to DC?