science

Height above average terrain

Height above average terrain is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Height above average terrain rather than just read about it. In short: Height above average terrain (HAAT), or (less popularly) effective height above average terrain (EHAAT), is the vertical position of an antenna site above the surrounding landscape. HAAT is used extensively in FM radio and television, as it is more important than effective radiated power (ERP) in determining the range of broadcasts (VHF and UHF in particular, as they are line of sight transmissions).

Key takeaways

Height above average terrain belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Height above average terrain to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Height above average terrain from memory before moving on to harder problems.

Reference excerpt

Height above average terrain (HAAT), or (less popularly) effective height above average terrain (EHAAT), is the vertical position of an antenna site above the surrounding landscape. HAAT is used extensively in FM radio and television, as it is more important than effective radiated power (ERP) in determining the range of broadcasts (VHF and UHF in particular, as they are line of sight transmissions). For international coordination, it is officially measured in meters, even by the Federal Communications Commission in the United States, as Canada and Mexico have extensive border zones where stations can be received 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 (see List of North American broadcast station classes for more information on this). The FCC procedure to calculate HAAT is: from the proposed or actual antenna site, either 12 or 16 radials are drawn, and points at 2, 4, 6, 8, and 10 miles (16 km) radius along each radial were used. The entire radial graph could be rotated to achieve the best effect for the station. The altitude of the antenna site, minus the average altitude of all the specified points, is the HAAT. This can create some unusual cases, particularly in mountainous regions—it is possible to have a negative number for HAAT (the transmitter would not be located underground, but rather in a valley, with hills on both sides taller than the transmitter itself, for example). The FCC has divided the Contiguous 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 prevent co-channel interference.

The FCC regulations for ERP and HAAT are listed under Title 47, Part 73 of the Code of Federal Regulations (CFR).

Zones I and I-A Maximum HAAT: 150 metres (492 ft 2 in) Maximum ERP: 50 kilowatts (47dBW) Minimum co-channel separation: 241 km (150 mi)

Zones II and III Maximum HAAT: 600 metres (1,968 ft 6 in) Maximum ERP: 100 kilowatts (50dBW) Minimum co-channel separation: 290 km (180 mi).

TV In all zones, maximum ERP for analog TV transmitters is as follows:

VHF 2-6: 100 kilowatts (50dBW) (analog); 45 kilowatts (46.5dBW) (digital) VHF 7-13: 316 kilowatts (55dBW) (analog); 160 kilowatts (52dBW) (digital) UHF: 5,000 kilowatts (67dBW) (analog); 1,000 kilowatts (60dBW) (digital)

Maximum HAAT Zone I: 305 metres (1,000 ft 8 in) Zones II and III: 610 metres (2,001 ft 4 in)

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, and West Virginia; in addition to the northern and eastern portions of Virginia; the areas of Michigan and southeastern Wisconsin south of 43° 30' north latitude; the coastal strip of Maine; the areas of New Hampshire and Vermont south of 45° north latitude; and the areas of western New 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 of California south of 40° north latitude, Puerto Rico and the U.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 of Alabama, Georgia, Louisiana, Mississippi, and Texas within approximately 241.4 kilometers (150.0 mi) of the Gulf of Mexico. Zone II is all the rest of the Continental United States, Alaska and Hawaii.

See also Above mean sea level (AMSL) Above ground level (AGL) Canadian Radio-television and Telecommunications Commission (CRTC) List of broadcast station classes Topographic prominence – a similar measurement for mountains

External links 47 CFR Part 73 Index (2005) Archived 2011-07-17 at the Wayback Machine FCC: Mass Media Calculated Contours FCC: HAAT Calculator "Superpower" Grandfathered FM stations Archived 2016-07-06 at the Wayback Machine

Illustrations

Worked examples

Example 1 — a first encounter with Height above average terrain

Start with the simplest possible case. Write down what Height above average terrain claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Height above average terrain before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Height above average terrain ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Height above average terrain

In research: Height above average terrain appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Height above average terrain in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Height above average terrain is common in secondary-school and first-year university syllabi. It links to neighbouring topics Antennas, Broadcasting, Height, so understanding it makes those chapters shorter.
In everyday life: Look for Height above average terrain outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Height above average terrain in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Height above average terrain means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Height above average terrain out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Height above average terrain in simple terms?

Why does Height above average terrain matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Height above average terrain?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Height above average terrain.