List of North American Broadcast Station Classes - AM

AM

• A (former I): clear-channel stations, 10 kW to 50 kW day and night (Class I-N stations are only assigned to the non-conterminous United States, and then with a minimum power of 10 kW (and a maximum power of 50 kW) and Class B efficiency (although higher efficiency is acceptable)
• B (former II and III): 250 W to 50 kW (to 10 kW on 1620 kHz to 1710 kHz)
• D (former II-D, II-S, III-S): daytime 250 W to 50 kW, nighttime under 250 W or off-air, field strength up to 140 mV/m at 1 km, no new stations except downgraded B
• C (former IV): 250 W to 1 kW (also grandfathered 100 W)
• TIS/HAR: travelers' information stations up to 10 W transmitter output power, licensed by NTIA (not FCC) in U.S. national parks
• Unlicensed broadcasting (see low-power broadcasting): 100 mW DC input to final amplifier, no license needed, may be measured at edge of campus for school stations

Notes

• In the Western Hemisphere (ITU region 2), medium wave AM broadcasts are on channels spaced 10 kHz apart from 530 kHz to 1700 kHz, with certain classes restricted to subsets of the available frequencies.
• With few exceptions, Class A stations can be found only on the frequencies of 540 kHz, 640 to 780 kHz, 800 to 900 kHz, 940 kHz, 990 to 1140 kHz, 1160 to 1220 kHz, and 1500 to 1580 kHz. The exceptions are cited in relevant international treaties.
• While U.S. and Canadian Class A stations are authorized to operate at a maximum of 50,000 watts day and night (and a minimum of 10,000 watts at night, if grandfathered), certain existing Mexican Class A stations, and certain new Cuban Class A stations are authorized to operate at a higher power. Certain Mexican Class A stations are authorized to operate at less than 50,000 watts nights, if grandfathered, but may operate at up to 100,000 watts days.
• Class B and D stations can be found on any frequencies from 540 kHz to 1700 kHz except where frequencies have been reserved for Class C stations.
• Class C stations can be found in the lower 48 US states on the frequencies of 1230 kHz, 1240 kHz, 1340 kHz, 1400 kHz, 1450 kHz, and 1490 kHz (commonly known as "graveyard" frequencies). Other countries may use other frequencies for their Class C stations.
• Canada also defines Class CC (Carrier Current, restricted to the premises) and LP. (less than 100 watts)
• TIS stations can be found on any frequency from 530 kHz to 1700 kHz in the US, but may only carry non-commercial messages without music.
• Low-power AM stations located on a school campus are allowed to be more powerful, so long as their signal strength does not exceed roughly 14 to 45 µV/m² (depending on frequency) at a distance of 30 meters (98.4 ft) from campus.
• AM classes were previously assigned Roman numerals from I to IV in the US, with subclasses indicated by a letter suffix. Current class A is equivalent to the old class I; class B is the old classes II and III, with class D being the II-D, II-S, and III-S subclasses; and class C is the old class IV.
  • The following conversion table compares the old AM station classes with the new AM station classes: