802.11 Wireless Network Site Surveying and Installation

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