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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