If you are on a high mountain and there are also a lot of other high locations around you your HAAT number could still be low. If however you are on a high mountain and the rest of the area all the way around your site is much lower, your HAAT figure will go up. Sites built on side hill locations with the hill rising above in part of the radius will greatly reduce the HAAT number.
http://www.fcc.gov/mb/audio/bickel/haat_calculator.html "How is the HAAT determined? A HAAT value is determined by taking 50 evenly spaced elevation points (above mean sea level [AMSL]) along at least 8 evenly spaced radials from the transmitter site (starting at 0 degrees [True North]). The 50 evenly spaced points are sampled in the segment between 3 to 16 km (formerly 2 to 10 miles) along each radial. The elevation points along each radial are averaged, then the radial averages are averaged to provide the final HAAT value. Terrain variations within 3 km (2 miles) of the transmitter site usually do not have a great impact on station coverage." Brian From: wireless-boun...@wispa.org [mailto:wireless-boun...@wispa.org] On Behalf Of Fred Goldstein Sent: Thursday, September 23, 2010 4:36 PM To: WISPA General List Subject: Re: [WISPA] Transmit Antenna Height This item alone may be the show-stopper, the poison pill that makes it useless to WISPs in much of the country. In places where the routine variation in elevation is more than 75 meters, there will be houses (subscribers) that are more than 76 meters AAT. I notice this in the areas I'm studying, both in the east and in the upper midwest. In a place like Kansas, nobody is >75m AAT. But in the woody Berkshires of Western Massachusetts, the UHF space is needed to get through the trees, and a significant share of houses are >75m AAT. Also, if you want to cover a decent radius, the access point needs to be up the hill too. 75 meters isn't a mountaintop; it's just a little rise. It makes no sense to absolutely ban fixed use at a site that is 100m AAT if the nearest protected-service contour is, say, 50 miles away. A more sensible rule would be to follow broadcast practice, and lower the ERP based on height, so that the distance to a given signal strength contour is held constant as the height rises. Hence a Class A FM station is allowed up to 15 miles, and if it is more than 300 feet AAT, then it is allowed less than the 3000 watts ERP that apply at lower heights. Maybe the lawyers want to have more petitions to argue over. At 9/23/2010 04:07 PM, Rich Harnish wrote: 65. Decision. We decline to increase the maximum permitted transmit antenna height above ground for fixed TV bands devices. As the Commission stated in the Second Report and Order, the 30 meters above ground limit was established as a balance between the benefits of increasing TV bands device transmission range and the need to minimize the impact on licensed services.129 Consistent with the Commission's stated approach in the Second Report and Order of taking a conservative approach in protecting authorized services, we find the prudent course of action is to maintain the previously adopted height limit. If, in the future, experience with TV bands devices indicates that these devices could operate at higher transmit heights without causing interference, the Commission could revisit the height limit. 66. While we expect that specifying a limit on antenna height above ground rather than above average terrain is satisfactory for controlling interference to authorized services in the majority of cases, we also recognize petitioners' concerns about the increased potential for interference in instances where a fixed TV bands device antenna is located on a local geographic high point such as a hill or mountain.130 In such cases, the distance at which a TV bands device signal could propagate would be significantly increased, thus increasing the potential for interference to authorized operations in the TV bands. We therefore conclude that it is necessary to modify our rules to limit the antenna HAAT of a fixed device as well as its antenna height above ground. In considering a limit for antenna HAAT, we need to balance the concerns for long range propagation from high points against the typical variability of ground height that occurs in areas where there are significant local high points - we do not want to preclude fixed devices from a large number of sites in areas where there are rolling hills or a large number of relatively high points that do not generally provide open, line-of-sight paths for propagation over long distances. We find that limiting the fixed device antenna HAAT to 106 meters (350 feet), as calculated by the TV bands database, provides an appropriate balance of these concerns. We will therefore restrict fixed TV bands devices from operating at locations where the HAAT of the ground is greater than 76 meters; this will allow use of an antenna at a height of up to 30 meters above ground level to provide an antenna HAAT of 106 meters. Accordingly, we are specifying that a fixed TV bands device antenna may not be located at a site where the ground HAAT is greater than 75 meters (246 feet). The ground HAAT is to be calculated by the TV bands database using computational software employing the methodology in Section 73.684(d) of the rules to ensure that fixed devices comply with this requirement. 130 The antenna height above ground is the distance from the antenna center of radiation to the actual ground directly below the antenna. To calculate the antenna height above average terrain (HAAT), the average elevation of the surrounding terrain above mean sea level must be determined along at least 8 evenly spaced radials at distances from 3 to 16 km from the transmitter site. The HAAT is the difference between the antenna height above mean sea level (the antenna height above ground plus the site elevation) and the average elevation of the surrounding terrain. 67. In reexamining this issue, we also note that the rules currently do not indicate that fixed device antenna heights must be provided to the database for use in determining available channels. It was clearly the Commission's intent that fixed devices include their height when querying the database because the available channels for fixed devices cannot be determined without this information.131 We are therefore modifying Sections 15.711(b)(3) and 15.713(f)(3) to indicate that fixed devices must submit their antenna height above ground to the database. 68. We continue to decline to establish height limits for personal/portable devices. As the Commission stated in the Second Report and Order, there is no practical way to enforce such limits, and such limits are not necessary due to the different technical and operational characteristics of personal/portable devices. -- Fred Goldstein k1io fgoldstein "at" ionary.com ionary Consulting http://www.ionary.com/ +1 617 795 2701
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