The Basics of Radio Electronics
Radio — the electronic technology if not the audio programming — has never been more popular than it is right now. In the 1930s and '40s, there was only one use for radio: broadcast audio signals. Today, audio broadcast over radio is as commonplace as ever, but the list of other types of information being broadcast by radio technology has skyrocketed.
Most people think of radio as wireless broadcast of sound, most often music and speech. But the term radio is actually much broader than that; the broadcast of sound is actually just one application of the extremely useful electrical phenomenon that is called radio.
Broadcast television is nothing more than the combination of audio and video broadcast over radio. Cellphones use radio to extend the world’s telephone networks. Then there was wireless networking and cellular data plans, which transmit Internet data over radio. And there are many other popular uses for radio technology, including radar, GPS navigation systems, and wireless Bluetooth devices.
Radio takes advantage of one of the most interesting of all electrical phenomena: electromagnetic radiation (often abbreviated EMR), which is a type of energy that travels in waves at the speed of light. EMR travels freely through the air and even in the vacuum of space.
EMR waves can oscillate at any imaginable frequency. The rate of the oscillation is measured in cycles per second, also known as hertz (abbreviated Hz). Instead, it honors the great German physicist Heinrich Hertz, who was the first person to build a device that could create and detect radio waves.
Radio is simply a specific range of frequencies of EMR waves. The low end of this range is just a few cycles per second, and the upper end is about 300 billion cycles per second (also known as gigahertz, abbreviated GHz.) That’s a pretty big range, but EMR waves with much higher frequencies exist as well, and are in fact commonplace.
EMR waves with frequencies higher than radio waves go by various names, including infrared, ultraviolet, X-rays, gamma rays, and — most importantly — visible light.
That’s right; what we call light is exactly the same thing as what we call radio, but at higher frequencies. The frequency of visible light is measured in billions of hertz, also called terahertz and abbreviated THz. The low end of visible light (red) is around 405THz and the upper end (violet) is around 790 THz.
So here’s an interesting thought to ponder: Radio stations broadcast on a specific frequency. For example in San Francisco, there's a popular radio station called KNBR, which has been broadcasting on the frequency 680 kHz since 1922. There are plenty of other radio stations in the area, but only KNBR broadcasts at 680 kHz.
The term channel is often used to refer to a radio station broadcasting at a particular frequency.
Purple is the color we perceive when we see light whose frequency is right around 680 THz. There are many other colors, but only the color purple is at 680 THz.
In a way, color is the same thing as channel. If EMR waves are vibrating at 680 kHz, they are KNBR radio. If those same EMR waves are vibrating a million times faster, at 680 THz, they are the color purple.
An important concept that’s related to frequency is the idea of wavelength. The term wavelength refers to the distance between the crests of each cycle of EMR at a particular frequency. Because EMR waves travel at the speed of light, you can calculate the wavelength of a given frequency by dividing the distance that light travels in a single second by the number of cycles per second.
The higher the frequency, the shorter the wavelength. The wavelength of most AM broadcast radio stations is a few hundred feet. The wavelength of visible light is a very small fraction of an inch.