The Physics – and Mystery – of Radio

When I was a kid, I had a pair of Star Wars walkie talkies that I got for Christmas one year. They were especially cool because, instead of just being single handheld units like “normal” walkie talkies, they came with headsets that you could wear, meant to look like the headsets worn by Luke and Han during the TIE fighter attack scene in A New Hope. I can remember being 9 or 10, playing by myself outside with one of these walkie talkies when suddenly, I could hear something coming through the earpiece. They were voices…

A Real “Radio Drama”

Where were these fuzzy, faint voices coming from? No one was using my other walkie talkie; it was turned off in my room. What had I stumbled upon? Sometimes I would hear the voices and then other times, just static. So as the young budding scientist I was, I started experimenting with the antenna of the walkie talkie, holding it up as high as I could, changing its orientation, and even holding it up against large metal objects like stop sign posts. For weeks and months after, I made it my mission to investigate this strange and somewhat disturbing phenomenon that was coming to me through a child’s toy.

What appeared to be so mysterious to me at the time turned out to be somewhat less mysterious than I originally thought: I had been picking up CB radio transmissions from truckers and such on my badly-tuned walkie talkie – a conclusion that seems painfully obvious to me now as someone with a Ph.D. in physics, but as a kid, it might as well have been magic. I had discovered the magic of electromagnetic waves, or more specifically, radio waves. But even today with my background in physics, for me, radio communication still has this tinge of mystery to it. From time to time I still fiddle around with the old radio scanner that my grandpa once gave me. (Shoutout to the local hams on 462.625 MHz!) It’s kind of bizarre that I can turn on my scanner and then, seemingly out of nowhere, out come these peculiar voices. With no [easy] way of determining from where these voices originate, they might as well be coming from another dimension.

The Physics Behind Your Radio

“So, Dr. Jake,” you ask. “How exactly do these ‘electromagnetic waves’ work? And how do we use radio waves to communicate information?” Well, the basic idea comes down to “wiggling” electric charges. Imagine a radio station with a transmitter antenna at point A, and a few miles away you are driving down the road at point B with a receiver antenna mounted to the top of your car. Basically, when we wiggle a bunch of electrons at point A (by sending massive currents up and down the radio station’s transmitter antenna), it causes electrons at point B (i.e., the electrons inside your car’s radio antenna) to wiggle the same way. Your car radio senses these wiggles in your antenna and then translates them into the music on your favorite radio station.

The way we “encode” information into these transmissions is by manipulating the frequency and amplitude of our radio waves. The rate at which the current is fluctuating up and down in the radio station’s transmitter antenna determines the frequency of the wave. The amount of current used in this process determines the amplitude (or strength) of the wave. The next step involves holding one value constant and then changing (or modulating) the other value. By holding the frequency of a wave constant but modulating its amplitude, we get AM radio (“AM” stands for “amplitude modulation”). By holding the amplitude of a wave constant but modulating its frequency, we get FM radio (“FM” stands for “frequency modulation”). (Note: As is the case with any wave, there has to be something, or some value, going up and down. In the case of a wave on the ocean, it’s the literal surface of the water that’s moving up and down. In the case of an electromagnetic wave, it’s the intensity of the wave’s electric and magnetic fields that are fluctuating up and down, periodically, over time and space. So when we talk about the strength of an electromagnetic wave, we’re referring to its maximum electric and magnetic field values.)

To learn more about how radios and electromagnetic waves work, check out this great video from Techquickie. Also take a look at this awesome online physics simulation developed by the University of Colorado Boulder, which really brings the subject of this blog post to life. I actually used this website quite a bit as a teaching assistant in grad school and it’s chock-full of great STEM simulations that serve as wonderful teaching tools in the classroom or at home. While you’re at it, check out our website to  check out the micro:bit. These microcontrollers are specifically designed with STEM education in mind and can even communicate with each other via – you guessed it – radio waves! Until next time.

 – Dr. Jake Roark