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
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: 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
- 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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