Methods of Transmission Part I: Modulation—Sending Information Via Radio
Sending information using radio waves has impacted almost every aspect of our daily lives. Radio waves connect our cellphones to the network for phone calls and Internet use. When we listen to AM or FM radio stations—or off-air television—radio waves do the heavy lifting. Internet over Wi-Fi? Yep, that’s radio too.
Early Applications of Radio Waves
What are these wild, magical things called radio waves, and how can they be tamed to carry the information we depend on for so many things? What do all these funny terms mean: AM, FM, SSB, to mention just a few? In this series, we’ll demystify, as much as we can, how all this works and what all these terms mean. But first, a little history.
Radio got its start over 100 years ago, and none of the early applications centered around carrying the human voice. Nikola Tesla used radio waves to transmit electrical power wirelessly. While his invention was successful, it never worked out as a practical solution. He also used radio waves for remote control of model ships, novel but not exactly earth-shaking. Marconi came along and realized that radio could be used to send telegraph messages. The transmitters were crude but did the job, more or less. Later, pioneers developed the ability to send voice and music over radio waves, and the broadcasting industry was born. Nowadays, radio carries voice, data, video, and a host of other information. We have come a long way in a relatively short time!
Understanding Electromagnetic Waves
So, what are these things called radio waves? Well, technically, they are “electromagnetic waves,” so let’s unpack that. Electromagnetic implies that these are waves that, instead of sound in air or waves in water, are electromagnetic in nature. What does that mean? Radio waves have a dual nature: They have both an electrical component (electro) and a magnetic component (magnetic).
It turns out that electricity and magnetism are related. Spin a coil of wire in a magnetic field, and you get electricity, which is the basis of generators. So, imagine, if you will, a varying magnetic field with a corresponding electrical field. When you put a wire in that field (they call those wires “antennas”), you get a small electrical signal. It turns out the reverse is true: If you run an alternating current through a wire, it can act like an antenna and radiate an electromagnetic wave. This simple explanation doesn’t cover all there is to know about radio waves, but you get the basic idea. The physics of radio waves is complex, so we’ll leave more detailed explanations to the college professors.
Sending Information on Radio Waves
So, how do we send information on radio waves? The answer is both simple and complex. On the most basic level, the answer is simple: we change the characteristics of the radio wave. For example, the early radiotelegraph systems worked by turning the radio transmitter on and off. A telegraph key was connected to the transmitter, and the radio operator used Morse code to send information in the form of dots and dashes, short and long bursts of radio waves, a technique still used by some Ham radio operators today.
Crude but effective, this form of modulation is known as on-off keying, or OOK for short. This method is still used in a variety of low-cost wireless products, such as many garage door opener remotes.
There are many ways to vary–or modulate–a radio signal. From transmitting telegraph messages to carrying voice, data, video, and a host of other information, radio waves have played a vital role in shaping the modern world. While their physics and modulation techniques may be complex, the basic idea of changing the characteristics of the radio wave to send information is simple.
In our next installment, we’ll start with the earliest of methods still in use today: amplitude modulation, or AM.