Brian
*From:* wireless-boun...@wispa.org [
mailto:wireless-boun...@wispa.org] *On Behalf Of *Tom DeReggi
*Sent:* Thursday, September 23, 2010 7:32 PM
*To:* WISPA General List
*Subject:* Re: [WISPA] Transmit Antenna Height
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 <mailto:fgoldst...@ionary.com>
To: WISPA General List <mailto:wireless@wispa.org>
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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