Antenna Connectors and Remote Antennas
The FCC regulations impose limitations and restrictions on
antennas and connectors that may be used in a 2.4-GHz or 5-GHz WLAN system.
Although the FCC wrote these regulations, a few other countries have also
adopted them. Because of increased popularity of WLAN in the United States, and
the desire to build units as a single model, many vendors just follow the same
rules for connectors for all the products shipped worldwide.
The Code of Federal Regulations, Part 15.203, states that an
intentional radiator (transmitter) must be designed so the user cannot use an
antenna that was not provided for the transmitter. The rationale behind this is
to prevent the use of improper antennas, which can cause improper action of the
transmitter, and to prevent the use of antennas that exceed the maximum
permitted gain.
To comply, the regulations suggest that the antenna be
permanently attached, or that a unique connector be used. The regulations state
that a standard antenna connector is prohibited. The FCC has unofficially stated
that their interpretation of a unique connector implies that the connector
cannot be readily available to the general public. This antenna and connector
requirement does not apply to certain carrier current devices or to devices
operated under the provisions of Parts 15.211, 15.213, 15.217, 15.219, or
15.221.
One area of confusion regarding the regulations is this
statement: "This requirement does not apply to intentional radiators that must
be professionally installed or to other intentional radiators, which, in
accordance with §15.31(d), must be measured at the installation site."
However, the regulations go on to state, "The installer shall
be responsible for ensuring that the proper antenna is employed so that the
limits in this part are not exceeded."
The statement was intended to provide those who install more
complicated wireless systems, such as long-range broadband fixed wireless
systems or wireless perimeter security systems, with the flexibility they need.
The meaning of professionally installed is a subjective one, and the definition
is not provided in the regulations. Using a definition straight out of a
dictionary, a professional is anyone who receives any compensation for services
or work, and there are no ties to licensing or certification. However, if an
installer claims that he is a professional installer, and exercises this
exemption, he becomes the responsible party. As the responsible party,
noncompliance with FCC regulations makes the installer subject to fines and even
imprisonment.
This exemption afforded professional installers is intended to
allow them the design flexibility to shape antenna coverage patterns that allow
for maximum power density and, of course, do so in a manner that will not
violate any part of the regulations. Professional installers must consider two
factors as part of their customer installations. First, applying maximum power
to a specific antenna or area is far from the accepted normal practice. A
considerable amount of radio interference comes from existing radio systems
already installed and operating. Frequency planning mitigates this to a large
extent, but the experienced professional installer will typically use the
minimum power necessary to provide suitable link margins and performance.
Second, the professional installer tends to use antennas that shape the RF beams
no wider than absolutely necessary to provide suitable link margins. This in
turn helps provide suitable reliability and performance, with minimum
interference offered or received from adjacent radios systems.
In legal terms, this statement requires the installer to test
the system, once installed, to verify it complies with all regulations,
including transmitted emissions that are generated outside of the legal band,
noise generated by the receiver, and overall EIRP ratings. In most cases, these
types of measurements are well beyond the scope of most WLAN installers.
In mid-2004, the FCC made some changes to Part 15.204 regarding
the use of antennas that were not certified by the manufacturer of the
transmitter. Basically it states that any antenna may use the transmitter, as
long as it is of a similar type (omni-directional, patch, Yagi, dish, and so on)
and that it is of equal or lesser gain. It also cites the manufacturer of the
WLAN gear with the responsibility of providing users a list of antennas that
have been certified.
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