Modulation — Putting Your Voice on a Radio Wave - Basic Radio Theory

Modulation — Putting Your Voice on a Radio Wave

What is Modulation?

A plain radio wave (called the carrier) doesn't carry any information by itself — it's just a steady tone. To send voice, data, or Morse code, you need to modify (modulate) the carrier in some way. The three common methods are:

AM — Amplitude Modulation

Your voice changes the strength (amplitude) of the carrier wave. Think of it as making the wave taller and shorter in time with your voice.

Used by AM broadcast radio
Simple but not very efficient — wastes power on the carrier
Not commonly used in amateur radio (SSB is preferred)

FM — Frequency Modulation

Your voice changes the frequency of the carrier — making it slightly higher and lower in time with your voice. The amplitude stays constant.

Used on 2 metre and 70 cm repeaters — the most common mode for Foundation operators
Good audio quality, resistant to noise
Uses more bandwidth than SSB

SSB — Single Sideband

A more efficient version of AM. It removes the carrier and one sideband, transmitting only the essential information. Much more efficient with power and bandwidth.

Used on HF bands for voice contacts
LSB (Lower Sideband) is used below 10 MHz
USB (Upper Sideband) is used at 10 MHz and above

CW — Morse Code

The carrier is simply turned on and off to create dots and dashes. The simplest form of modulation, and the most efficient — CW can get through when voice can't.

For the Foundation exam: Know that FM is used on VHF/UHF repeaters, SSB is used on HF for voice, and CW is Morse code. You don't need to learn Morse code for the Foundation license.