This is the . Domestic classes are listed as subitems under international ones. Effective Radiated Power (ERP) and Height Above Average Terrain (HAAT) are listed unless otherwise noted.
The United States , Canada , and Mexico . All Broadcast Station s within 320 Kilometer s (about 200 Mile s) of the U.S.-Canada or U.S.-Mexico Border must get approval by both the domestic and foreign agency. These are the CRTC in Canada, the FCC in the U.S., and the SCT in Mexico.
- (former '''I'''): Clear Channel s, 10 kW to 50 kW day and night
- (former '''II''' and '''III'''): 250 W to 50 kW (to 10 kW on 1620 to 1710 kHz)
- --- (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/m2 at 1 km, no new stations except Downgraded B
- (former '''IV'''): 250 W to 1 kW (also Grandfathered 100 W)
- /'''HAR''': Travelers' Information Stations up to 10 W transmitter output power
- (see Low-power Broadcasting ): 50 mW, no license needed (US only?), may be measured at edge of campus for school stations
- In the Western Hemisphere ( ITU Region 2 ), Mediumwave AM broadcasts are on channels spaced 10 kHz apart from 530 kHz to 1710 kHz, with certain classes restricted to subsets of the available frequencies.
- Class A stations can be found only on the frequencies of 540 kHz, 640 to 780 kHz, 800 to 900 kHz, 940 kHz, 1000 to 1140 kHz, 1160 to 1220 kHz, and 1500 to 1580 kHz.
- 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. Other countries may use other frequencies for their Class C stations.
- 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.
See also: North American Radio Broadcasting Agreement (NARBA)
- : 100 kW, 300 m to 600 m, 91.8 km
- : 100 kW, 300 m to 450 m, 83.4 km
- : up to 100 kW, under 300 m, 72.3 km
- : up to 50 kW, up to 150 m, 52.2 km
- : up to 25 kW, up to 100 m, 39.1 km
- : up to 50 kW, up to 150 m, 65.1 km
- : up to 25 kW, up to 100 m, 44.7 km
- : 100 W to 6 kW, up to 100 m, 28.3 km
- --- (Mexico): up to 3 kW, the former limit for A
- : up to 250 W ERP, except U.S. non- Translator s to 10 W TPO
- --- (U.S., also '''LP100'''): 50 W to 100 W ERP, up to 30 m, 5.6 km
- --- (U.S., also '''LP10'''): 1W to 10 W ERP, up to 30 m
- Unlicensed: 250 µV/m2 at 3 m in U.S., 100µV/m2 at 30 m in Canada
Notes:
- Canada protects all Radio Station s out to a Signal Strength of 0.5 MV/m2 , whereas only commercial B stations in the U.S. are. Commercial B1 in the U.S. is 0.7mV/m2, and all other stations are 1.0 mV/m2. Noncommercial-band stations (88.1 to 91.9) are not afforded this protection, and are treated as C3 and C2 even when they are B1 or B. C3 and C2 may also be reported internationally as B1 and B, respectively.
- Class C0 is for former C stations, demoted at request of another station which needs the downgrade to accommodate its own facilities.
- In practice, many stations are above the maximum HAAT for a particular class, and correspondingly must downgrade their power to remain below the reference distance. Conversely, they may ''not'' increase power if they are ''below'' maximum HAAT.
- All class D (including L1 and L2 LPFM and translator) stations are secondary in the U.S., and can be bumped or forced off-air completely, even if they are not just a repeater and are the only station a licensee has.
- The United States is divided into separate regions that have different restrictions for FM stations. Zone I (much of the U.S. Northeast and Midwest ) and I-A (most of California , plus Puerto Rico ) is limited to classes B and B1, while Zone II (everything else) has only the C classes. All areas have the same classes for A and D.
- Power and height restrictions were put in place in 1962 . A number of previously-existing stations were Grandfathered in, such as KRUZ in Santa Barbara, California and WMC-FM in Memphis, Tennessee .
Zone I in the U.S. includes all of Connecticut , the District Of Columbia , Delaware , Illinois , Indiana , Massachusetts , Maryland , New Jersey , Ohio , Pennsylvania , Rhode Island , and West Virginia . It also includes the areas south of Latitude 43.5°N in Michigan , New Hampshire , New York , and Vermont ; as well as coastal Maine , southeastern Wisconsin , and northern and eastern Virginia .
Zone I-A includes California south of 40°N, as well as Puerto Rico and the U.S. Virgin Islands .
- full-service stations (suffix: -TV or -DT, -DS for temporary Digital permits):
- ---VHF low (2-6): 100 kW video, 10 kW audio; 20 kW digital
- ---VHF high (7-13): 325 kW video, 32.5 kW audio; 65.0 kW digital
- ---UHF all (14-69): 5 MW video, 500 kW audio; 1MW digital
- class stations (U.S.) (suffix: -CA or -DC):
- ---VHF all (2-13): 3 kW video, 300 W audio; 3 kW digital
- ---UHF all (14-69): 150 kW video, 15 kW audio; 30 kW digital
- LPTV (secondary) (suffix: -LP, -TX, for translators, or -DL / -LD, for low-power digital stations):
- ---VHF all (2-13): 3 kW video, 300 W audio; 3 kW digital
- ---UHF all (14-69): 150 kW video, 15 kW audio; 30 kW digital
- Experimental
- Unlicensed: not allowed except for Medical Telemetry , and certain Wireless Microphone s
- ---
Broadcast Translator s, Booster s, and other LPTV Station s are secondary, unless they have upgraded to class A. Class A is still considered LPTV with respect to stations in Canada and Mexico.
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