76 Chapter 3: Regulating the Use of 802.11 WLANs
qualified transmitter. This is to prevent improper or illegal installation with unapproved
transmitters. In plain English, unless the amplifier manufacturer submits the amplifier for
testing with a given transmitter, the amplifier cannot legally be sold in the U.S. for use with
that particular transmitter. If the amplifier has been certified, it must be labeled with an FCC
identification number citing its certification testing.
If you are using a system that includes a legal amplifier, remember that the rules concerning
power still apply. If the amplifier is 1/2 watt (27 dBm), this means in a multipoint system
the maximum antenna gain is only 9 dBi, and in a point-to-point system it is only 15 dBi.
(27 dBm is 3 dB below 30 dBm, so the gain of a multipoint antenna can be increased from
6 dBi, by 3 dB, for a total of 9 dBi. For a point-to-point system, it can be increased by a
total of 9 dBi, for a maximum of 15 dBi.)
In the ETSI regulations, there is a maximum EIRP limit of 20 dBm. Because most amp-
lifiers start off well above this level, they are usually not permitted.
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 regu-
lations, 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 (trans-
mitter) 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 pro-
hibited. 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

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