- Height above average terrain
Height above average terrain (HAAT) (or less popularly, EHAAT, Effective Height Above Average Terrain) is used extensively in FM
radio andtelevision , as it is actually much more important thaneffective radiated power (ERP) in determining the range of broadcasts (VHF and UHF in particular, as they are line of sight transmissions). Forinternational coordination, it is officially measured in meters, even by theFederal Communications Commission in theUnited States , asCanada andMexico (both of which use metric) have extensive border zones where international stations can be heard on either side of the international boundaries. Stations that want to increase above a certain HAAT must reduce their power accordingly, based on the maximum distance their station class is allowed to cover (seelist of broadcast station classes for more information on this).Before metrification at the FCC, the procedure to figure HAAT was relatively simple: from the proposed or actual antenna site, either 12 or 16 radials were drawn, and points at 2, 4, 6, 8, and convert|10|mi|km radius along each radial were used. The entire radial graph could be rotated to achieve the best effect for the station. The average altitude of all the specified points, minus the altitude of the antenna site, was the HAAT. This can create some unusual cases, particularly in
mountain ous regions—it is possible to have a negative number for HAAT (the transmitter would not be located underground, but rather in avalley , with hills on both sides taller than the transmitter itself, for example).The FCC has divided the
Continental United States into three zones for the determination of spacing between FM and TV stations using the same frequencies. FM and TV stations are assigned maximum ERP and HAAT values, depending on their assigned zones, to preventCo-channel interference .The FCC regulations for ERP and HAAT are listed under Title 47, Part 73 of the
Code of Federal Regulations (CFR).FM
Zones I and I-A
*Maximum HAAT: 150 meters (492 ft)
*Maximum ERP: 50 kW
*Minimum co-channel separation: 241 km (150 miles)Zones II and III
*Maximum HAAT: 600 meters (1968 ft)
*Maximum ERP: 100 kW
*Minimum co-channel separation: 290 km (180 miles).TV
In all zones, maximum ERP for analog TV transmitters is as follows:
*VHF 2-6: 100 kW
*VHF 7-13: 316 kW
*UHF: 5,000 kWMaximum HAAT
*Zone I: 305 meters (1000 ft)
*Zones II and III: 610 meters (2000 ft)Minimum co-channel separation
Zone layouts
Zone I (the most densely populated zone) consists of the entire land masses of the following states:
Connecticut ,Delaware ,Illinois ,Indiana ,Maryland ,Massachusetts ,New Jersey ,Ohio ,Pennsylvania ,Rhode Island , andWest Virginia ; in addition to the southern and eastern portions ofVirginia ; the areas ofMichigan and southeasternWisconsin south of 43° 30' north latitude; the coastal strip ofMaine ; the areas ofNew Hampshire andVermont south of 45° north latitude; and the areas of westernNew York south of 43° 30' north latitude and eastern New York south of 45° north latitude. In addition, Zone I-A (FM only) consists of all ofCalifornia south of 40° north latitude,Puerto Rico and theU.S. Virgin Islands . (If the dividing line between Zones I and II runs through a city, that city is considered to be in Zone I.)Zones I and I-A have the most "grandfathered" overpowered stations, which are allowed the same extended coverage areas that they had before the zones were established. One of the most powerful of these stations is WBCT in
Grand Rapids, Michigan , which operates at 320,000 watts and 238 meters (781 ft) HAAT.Zone III (the zone with the flattest terrain) consists of all of
Florida and the areas ofAlabama , Georgia,Louisiana ,Mississippi , andTexas within approximately 241.4 kilometers (150 miles) of theGulf of Mexico .Zone II is all the rest of the Continental United States,
Alaska andHawaii .ee also
*
Above mean sea level (AMSL)
*Above ground level (AGL)
*Canadian Radio-television and Telecommunications Commission (CRTC)
*List of broadcast station classes
*United States Federal Communications Commission (FCC)External links
* [http://www.access.gpo.gov/nara/cfr/waisidx_05/47cfr73_05.html 47 CFR Part 73 Index (2005)]
* [http://ftp.fcc.gov/oet/info/maps/mmb/ FCC: Mass Media Calculated Contours]
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