Yeah, that really sucks. Many areas needing served have thick forest/trees
easilly 70ft tall.
A 90ft height, just wouldn't allow enough of the signal to have open air, and
the signal would be going through trees most of the full path.
In 900Mhz, the difference between having the tower side over the tree line and
below the tree line can be the difference between a quarter mile coverage and a
7 mile coverage in our market.
All be it, 700Mhz does have better NLOS propogation characteristics than 900
does.
I would have liked to see that height doubled.
However, admittedly, it will allow much better spectrum re-use in areas that
have a limited number of channels available.
Spectrum reuse is one of the best ways to serve more people.
Tom DeReggi
RapidDSL & Wireless, Inc
IntAirNet- Fixed Wireless Broadband
----- Original Message -----
From: Fred Goldstein
To: WISPA General List
Sent: Thursday, September 23, 2010 4:36 PM
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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