Understanding the Frequency Allocation of FM Radio: Why 87.5 to 107.9 MHz?

FM radio stations are assigned frequencies within a specific range: 87.5 to 107.9 MHz. This range is a result of regulatory decisions made to optimize broadcast quality, minimize interference, and adhere to international agreements. In this article, we will explore the main reasons behind this specific frequency allocation for FM radio.

Interference Avoidance: Why 87.5 to 107.9 MHz?

The primary reason for selecting this frequency range is to minimize interference between stations. The International Telecommunication Union (ITU) established the 87.5 to 108.0 MHz band as part of the global radio frequency allocation. This creates uniformity across different countries for FM broadcasting. Frequencies are spaced 200 kHz apart to prevent overlap and ensure clearer reception.

Technical Considerations: Why Not Other Frequencies?

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Historical and Regulatory Factors: Why 87.5 to 107.9 MHz?

The frequency bands are allocated by the three global regions: Americas, Europe, and Africa. Many of these allocations are historic, meaning they were established before countries got together to establish global standards. However, when focusing on the FM radio standard in North America, the 87.5 to 107.9 MHz range is a result of regulatory decisions.

The AM vs. FM Bandwidth

When you compare the AM and FM bands, the 87.5 to 107.9 MHz range might seem narrow. However, the AM broadcast band covers a different frequency range: 550 kHz to 1700 kHz, or 550 to 1.7 MHz. In terms of actual frequencies, the AM band is about 20 times larger than the FM band.

The reason for this difference is that the "channels" in the FM band are wider and can thus carry more information. FM signals tend to sound much better and carry more ancillary information than AM signals. Today, a lot of information is crammed into AM channels, though they are naturally constrained by their narrower bandwidth.

Conclusion: The Significance of the 87.5 to 107.9 MHz Range

The 87.5 to 107.9 MHz frequency range for FM radio is crucial for clear broadcasting and minimal interference. Regulatory decisions made by the ITU and local authorities aim to optimize broadcast quality, adhere to global standards, and account for future needs. As technology evolves, this range will continue to serve as a cornerstone for FM broadcasting.

Additional Reading

If you are interested in learning more about radio frequency allocations and broadcasting standards, consult the ITU's guidelines and the FCC's regulations for North America. Staying informed about these regulatory frameworks can help you better understand the technical underpinnings of radio broadcasting.