Practical_Antenna_Handbook_0071639586

700 P a r t V I I I : M e c h a n i c a l C o n s t r u c t i o n a n d I n s t a l l a t i o n T e c h n i q u e s
Federal
In the United States, federal intervention takes two forms:
• Regulations to minimize hazards to aviation from man-Âmade structures that
rise far above the average terrain
• PRB-Â1, issued by the Federal Communications Commission (FCC) in 1985, preempting
certain aspects of local regulation of amateur radio structures
Within the United States the Federal Aviation Agency (FAA) maintains a database
of towers and antennas in excess of 200 ft above average terrain and/or close to public
airports. It will be necessary for you to notify both the FCC and the FAA prior to constructing
a tower or other man-Âmade antenna support structure that rises 200 ft or
more above the ground around it. Depending on the specifics of your site, your application
may be acceptable, but it will certainly require FAA-Âapproved lighting in all
instances.
Additionally, for potential tower installations in the vicinity of existing airports, the
FAA has a published formula that sets a maximum height for towers and any antennas
on them as a function of distance to the nearest runway. Actually, there are three individual
formulas to be concerned with:
• For airports with one or more runways longer than 3200 ft, the top of your antenna
or man-Âmade support cannot exceed 1 ft for every 100 ft between the
antenna and the nearest part of any runway at that airport. If you wish to put
up a 70-Âft tower, for instance, you must be at least 7000 ft (or approximately 1.3
mi) from the nearest part of the runway closest to your tower(s).
• For airports with no runways longer than 3200 ft, the top of your antenna or
man-Âmade support cannot exceed 1 ft for every 50 ft between your antenna and
the nearest part of any runway at that airport. This effectively doubles your allowable
antenna height at a given distance from an airport.
• For heliports, the corresponding limit is 1 ft of antenna height for every 25 ft
from your antenna and any portion of the helipad that is used for flight operations.
If the elevation above mean sea level (MSL) of the nearby airport is substantially different
from that at the base of your proposed tower(s), the calculation may be more
complicated than these bullet points indicate. When in doubt, submit an application to
the FAA and get a formal ruling for your files.
PRB-Â1
A quarter-Âcentury ago, the FCC issued a document now familiarly called “PRB-Â1”.
PRB-Â1 conveys “limited federal preemption” of local municipal restrictions on amateur
towers and antennas. It is potentially useful to you, depending on the specific objections
being raised by neighbors or local officials, but it is not a substitute for a clearly
worded permissive ordinance and/or a building permit. Occasionally you may encounter
a state or locality that has made blanket adjustments in its zoning ordinance in
response to PRB-Â1, but it’s primarily a tool for your attorney, should you reach that
point in negotiations with your county or town.