Set your car radio to 98.1. I hear noise, then music. It’s simple enough. But why not 98.2? or 98.0? The answer can be found in a century of bureaucratic decisions that seem completely arbitrary today.
In the United States, the Federal Communications Commission (FCC) allocates the FM frequency band between 88 and 108 MHz. This area is not based on any profound physical facts about sound waves. This is mostly history and a whim. Once the frequency bands were established, the FCC needed a way to install the stations without interfering with each other. They chose 200kHz slices. Each station has its own 200 kHz spectrum block.
Here’s the weird part. These slices all start with odd number boundaries. So 88.1, 88.3, 88.5. You won’t see 88.2 or 88.4 in the US. This is the rule. These are strong, arbitrary rules that regulators set a clear distinction between.
Europe took a different approach. Their FM station spacing is 100 kHz. Thanks to the tinny gap, it can be used with even or odd numbers. 88.0, 88.1, 88.2. All valid. The US stuck with its odd-numbered, wider gaps. The result was a radio dial with a uniquely American feel.
This separation prevents interference. When the stations overlap, the audio becomes a bunch of overlapping sounds and music. The 200 kHz gap gives the signal a bit of breathing space. This is not magic. This is a engineering constrained by history.
The FM radio plays music and audio. This is an analog signal. That’s probably why it sounds so warm. Depending on the receiver, it may be tinny. This technique is based on changing the carrier frequency. It is not the amplitude. Amplitude modulation (AM) is sensitive to static. This is not the case with FM. This is the main advantage.
But why does this matter now? We live in a digital world. Streaming services are common. You no longer need a physical antenna to listen to music. But the infrastructure remains. Millions of FM transmitters continue to send signals into the air. Spectrum is a limited resource. prescribed for a specific purpose. Mobile phones have their own frequency bands. Baby monitors have theirs. CB radios have theirs. They won’t talk because the FCC says they can’t.
The law of odd numbers is a thing of the past. This little piece of radio history is preserved because the change is expensive and complicated. Simply moving each station by 0.1 MHz does not avoid major logistical problems.
So the next time you listen to 101.5, remember the FCC. Remember the arbitrary choice. Note that 101.6 does not exist here. Probably in Europe. But that’s not the case here.
Frequently asked questions
What is FM radio used for?
Send music or audio signals. This is a technique that reduces static by changing the frequency of carrier waves.
Why do FM stations end in odd numbers?
The FCC reserves 200 kHz slices starting at odd-numbered boundaries. This prevents interference. In Europe, 100-kilohertz
