At 9/30/2010 10:37 PM, Jack Unger wrote:
Fred,
I'm sorry to seem dense but I don't understand your explanation
below. I'd appreciate it if you would re-explain. The FCC said:
"transmit antenna used with fixed devices may not be more than 30
meters above the ground. In addition, fixed devices may not be
located at sites where the height above average terrain (HAAT) at
ground level is more than 76 meters".
I'm trying to reconcile that with your statements. Could you please
re-explain more clearly or by using better actual numbers (both HAAT
at ground level and antenna height above ground)?
Thanks in advance,
jack
Sure. In the Order itself, the FCC explained the origin of the 76
meter HAAT limit. They explained that they didn't want any antennas
more than 106 meters AAT. That's the maximum antenna HAAT I referred
to. Since antennas are allowed to be 30 meters above ground, they
subtracted 30 from 106 and got 75. See paragraph 66 of the Order:
"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 Order cited an IEEE 802 Petitition
http://fjallfoss.fcc.gov/ecfs/document/view?id=6520201311 which
called for HAAT to be a factor. But they didn't call for a ban on
operation above 75 meters; rather, they wanted co-channel separation
to increase with height:
less than 3 meters | 6 km 0.1 km
3 Less than 10 meters* 6.9 km 0.256 km
10 Less than 30 meters 10.8 km 0.285 km
30 Less than 50 meters 13.6 km 0.309 km
50 Less than 75 meters 16.1 km 0.330 km
75 Less than 150 meters 22.6 km 0.372 km
150 Less than 300 meters 32 km 0.405 km
300 Less than 600 meters 45.7 km 0.419 km
600 meters or higher 68 km 0.426 km
That's rational. On the other hand I'd prefer allowing fixed devices
at any ground elevation, to allow everyone to subscribe, so I'd
suggest instead that they maximum ERP be decreased in order to limit
interference to the same level. So maybe 6 dB from 76 to 150 meters
and 10 dB to 300 meters, though that's a guess; I haven't run the
calculations. And I'd allow directional antennas, professionally
installed, to have ERP measured in the direction of the protected
contour, with no reduction in ERP if it's clear to the distance the
above chart.
I'm thinking about a petition to that effect. I have real subscriber
sites in mind.
On 9/23/2010 4:48 PM, Fred Goldstein wrote:
The rules allow antenna heights up to 30 meters, around 100
feet. One problem with the maximum HAAT limit is that it applies
to the ground height, based on having a 30 meter high antenna. In
other words, the ruling assumed a maximum antenna HAAT, and then
set the ground HAAT to be 30m below that. If somebody's house
is >10m below the limit, then a 10m antenna should be legal. (The
minimum antenna height went away, since sensing is no longer
required. That frankly seems to be the only major improvement in the rules.)
Brian
From:
<mailto:[email protected]>[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: <mailto:[email protected]>Fred Goldstein
To: <mailto:[email protected]>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/>http://www.ionary.com/
+1 617 795 2701
----------
--------------------------------------------------------------------------------
WISPA Wants You! Join today!
http://signup.wispa.org/
--------------------------------------------------------------------------------
WISPA Wireless List: <mailto:[email protected]>[email protected]
Subscribe/Unsubscribe:
http://lists.wispa.org/mailman/listinfo/wireless
Archives: http://lists.wispa.org/pipermail/wireless/
--------------------------------------------------------------------------------
WISPA Wants You! Join today!
http://signup.wispa.org/
--------------------------------------------------------------------------------
WISPA Wireless List: <mailto:[email protected]>[email protected]
Subscribe/Unsubscribe:
http://lists.wispa.org/mailman/listinfo/wireless
Archives: http://lists.wispa.org/pipermail/wireless/
--
Fred Goldstein k1io fgoldstein "at" ionary.com
ionary Consulting http://www.ionary.com/
+1 617 795 2701
--------------------------------------------------------------------------------
WISPA Wants You! Join today!
<http://signup.wispa.org/>http://signup.wispa.org/
--------------------------------------------------------------------------------
WISPA Wireless List: <mailto:[email protected]>[email protected]
Subscribe/Unsubscribe:
<http://lists.wispa.org/mailman/listinfo/wireless>http://lists.wispa.org/mailman/listinfo/wireless
Archives:
<http://lists.wispa.org/pipermail/wireless/>http://lists.wispa.org/pipermail/wireless/
--
Jack Unger - President, Ask-Wi.Com, Inc.
Author - "Deploying License-Free Wireless Wide-Area Networks"
Serving the Broadband Wireless, Networking and Telecom Communities since 1993
<http://www.ask-wi.com>www.ask-wi.com 818-227-4220
<mailto:[email protected]>[email protected]
--------------------------------------------------------------------------------
WISPA Wants You! Join today!
http://signup.wispa.org/
--------------------------------------------------------------------------------
WISPA Wireless List: [email protected]
Subscribe/Unsubscribe:
http://lists.wispa.org/mailman/listinfo/wireless
Archives: http://lists.wispa.org/pipermail/wireless/
--
Fred Goldstein k1io fgoldstein "at" ionary.com
ionary Consulting http://www.ionary.com/
+1 617 795 2701
--------------------------------------------------------------------------------
WISPA Wants You! Join today!
http://signup.wispa.org/
--------------------------------------------------------------------------------
WISPA Wireless List: [email protected]
Subscribe/Unsubscribe:
http://lists.wispa.org/mailman/listinfo/wireless
Archives: http://lists.wispa.org/pipermail/wireless/
