by frequency The following chart lists frequencies on the broadcast company band, and which classes broadcast on these frequencies; Class A and Class B, 10,000 watt and higher (full-time) stations in North America which broadcast on clear-channel station frequencies are also shown. By international agreement, Class A stations must be 10,000 watts and above, with a 50,000 watt maximum for the US and Canada, but no maximum for other governments in the region. Mexico, for example, typically runs 150,000 to 500,000 watts, but some stations are grandfathered at 10,000 to 20,000 watts at night; by treaty, these sub-50,000 watt Mexican stations may operate with a maximum of 100,000 watts during the daytime. Because the AM broadcast band developed before technology suitable for directional antennas, there are numerous exceptions, such as the US use of 800 (kHz) and 900 non-directionally in Alaska, limited to 5 kW at night; and 1050 and 1220, directionally, in the continental US, and without time limits; each of these being assigned to specific cities (and each of these being Mexican Class I-A clear channels). In return for these limits on US stations, Mexico accepted limits on 830 and 1030 in Mexico City, non-directionally, restricted to 5 kW at night (both of these being US Class I-A clear channels). FM Station class description Notes: Canada protects all radio stations out to a signal strength of 0.5mV/m (54dBu), whereas only commercial B stations in the US are. Commercial B1 in the US is 0.7mV/m (57dBu), and all other stations are 1.0mV/m (60dBu). 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 US, 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 regions that have different