Turn on the Radio!

A photo of my radio tuned to Power 104,300,000 Hz.

As soon as I sat down in my car today to go for a drive, I tuned my radio to Power 104.3 and heard the sweet sound of Taylor Swift’s “I Knew You Were Trouble” blasting through the speakers. Throughout all of the year’s that I’ve listened to the radio, I’ve always asked myself, “Why am I hearing this broadcast and why do I hear different broadcasts when I change the number on my radio’s tuner?” I always knew that radios worked because of transmission and reception of sound waves in the air, but, to be honest, I barely knew what a sound wave even was. Now, with sufficient knowledge of the physics of sound, I can easily explain to myself (and to all of you readers if you’d like) how you too can hear Taylor Swift blasting through your radio’s speakers.

A photo of me and a Taylor Swift life-size cut out.

When you tune your car’s radio to a radio station, for example, Power 104.3, have you ever asked yourself what those numbers actually mean? I didn’t think so. 104.3 is short for 104.3 MHz (megahertz.) That is, 104,300,000 Hz. Hertz, as we all know, is a frequency, represented by the equation f=1/T, where T is the period, the amount of time a sound wave takes to make a complete oscillation. We don’t necessarily need to know this, but the period of Power 104.3’s sound wave is T=1/104,300,000Hz=9.58×10^-9s, now that is one fast period! It makes sense that an FM radio station’s period would be so fast, it needs to transmit a lot of information really quickly in order to make a high quality broadcast. This explains why AM stations are not as high quality as FM stations, AM frequencies are only in kHZ as opposed to MHz.

Now that we’ve explained the basics of frequencies and periods of sound waves, how does your radio pick up these waves and relay their broadcast to your speakers? This is simple. Let’s use Power 104.3 as our example. Power 104.3’s transmitter’s sine wave has a frequency of 104.3MHz as previously stated. That’s great. We have a really fast sine wave moving through the air. Now what? Your car’s radio has a receiver complete with an antenna, tuner, and an amplifier. The radio receiver’s antenna picks up all of the radio sine waves traveling through the air. The tuner’s job is to then separate the one sine wave you want from all of the other sine waves. In our case, the tuner separated the 104.3MHz sound wave from all of the others. You may be asking, how does the tuner do this? That’s simple too. Tuners work using a principle called resonance. That is, the tuner resonates at one particular frequency and ignores all other frequencies in the air. Finally, the tuner sends the signal that it receives from a particular frequency to the radio’s amplifier, which ultimately amplifies the sine waves to your car’s speakers. Viola!

There you have it everyone, the physics of radios. Look above you! You see those? Those are radio waves. Thousands of them. Care to listen? Tell your tuner to resonate where you want it to!