Classes of U.S. FM stations:
Classes of U.S. FM stations:
U.S. FM radio stations come in 11 categories:
| | Minimum ERP (kw) | Maximum ERP (kw) | Minimum HAAT (m) | Maximum HAAT (m) |
| A | 0.1 | 6 | none | 100 |
| B1 | 6 | 25 | none | 100 |
| B | 25 | 50 | none | 150 |
| C3 | 6 | 25 | none | 100 |
| C2 | 25 | 50 | none | 150 |
| C1 | 50 | 100 | none | 299 |
| C0 | 100 | 100 | 300 | 449 |
| C | 100 | 100 | 450 | 600 |
| D | none | 0.01 | none | none |
| LP10 | none | 0.01 | none | 50? |
| LP100 | 0.1 | 0.1 | none | 50? |
I'm not certain of the HAAT limits for LP stations.
No new Class D stations are being authorized. Class D stations are limited to 10 watts transmitter output, the ERP may be slightly higher.
Class C0 is a relatively new development, there are very few such stations.
Yes, class B1 is the same as C3, and B the same as C2. Minimum distance separations between stations varies slightly though.
Stations may - and often do - exceed the listed maximum HAATs. When this happens, they must reduce power to compensate. On occasion, this reducation may lead to a power less than the listed minimum.
© D. Smith W9WI 2009
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