Chapter 3: Signal Theory and Modulation #

Now that you’ve learned about propagation and antenna systems, it’s time to focus on the signals themselves. How do we encode information onto radio waves? What makes different transmission modes unique? And how do these signals behave as they travel from transmitter to receiver?

As a General class operator, you have privileges on many bands using a variety of modulation methods. Understanding how these different modes work will help you choose the right technique for your communication needs, whether you’re chatting casually across town, participating in a worldwide contest, or providing emergency communications during a disaster.

In this chapter, we’ll explore both analog and digital modulation techniques. We’ll examine how single sideband (SSB) works, why it’s more efficient than AM, and how frequency modulation (FM) provides clarity in some situations. We’ll also dive into the exciting world of digital modes—from classic radioteletype (RTTY) to modern protocols like FT8 that can pull signals out of the noise.

We’ll also look at the technical aspects of signal bandwidth, frequency mixing, and how to avoid interference. These concepts aren’t just theoretical—they directly impact your on-air operations every time you turn on your radio.

Whether you’re upgrading your station for your new General class privileges or making the most of equipment you already have, understanding signal theory and modulation will help you communicate more effectively across all the frequencies now available to you. Let’s get started!