But how fast can 200 or 300MHz go?
On Thu, Sep 23, 2010 at 7:41 PM, Brian Webster
<[email protected] <mailto:[email protected]>>
wrote:
But what if you are able to use spectrum around 200 or 300 MHz?
That certainly goes through trees.
Brian
*From:* [email protected]
<mailto:[email protected]>
[mailto:[email protected]
<mailto:[email protected]>] *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:[email protected]>
*To:* WISPA General List <mailto:[email protected]>
*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
<http://ionary.com>
ionary Consulting http://www.ionary.com/
+1 617 795 2701
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