Rules, Regulations, and Legalities of Antenna Usage and Placement

The Federal Communications Commission (FCC) has been generous with its governance over the world of Wi-Fi communications. Because Wi-Fi operates in the unlicensed area of the broadcast spectrum, anyone can set up a wireless network. However, you should know some important regulations that concern your wireless network.

The Right Antenna for the Right Device

On July 12, 2004, the FCC issued rule 04-165, which has important implications for devices that operate in the 2.4-GHz and 5-GHz bands. As you recall, those are the bands in which 802.11a, 802.11b, and 802.11g reside.

The important part of this rule talks about "Replacement Antennas for Unlicensed Devices." Until this point, the FCC required any antenna used with a wireless device to be tested and certified as part of a system. That is, you could not mix and match equipment and antennas.

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Further, the FCC required unique connectors for each manufacturer and also required the development of new connectors as existing ones became prevalent.

Although you can go to a vendor and purchase antennas to connect with your wireless devices, there's a lawyer ball going on here. It's akin to buying a switchblade kit. The kit can be sold (and it's perfectly legal); however, assembling the kit is illegal.

The new FCC rule does not wave a magic hand across all antennas, providing broad and unrestricted legality. There are still some provisos.

When you use a replacement antenna (and the antenna is different than what was originally provided by the manufacturer) then such an antenna can be used, provided it is of the same family of antennas. That is, if it is a patch, omni, Yagi, and so on. Also, an antenna's gain must be equal to or less than the gain for which the manufacturer has attained approval. For example, if Cisco has certified a 13.5-dBi Yagi, a 13.5-dBi Yagi or lower gain antenna from another antenna vendor can be used.

Power Regulation

The FCC has not given carte blanche to wireless networks simply because they operate in the unlicensed bands of the spectrum. It still regulates how much power an antenna can output and gain.

In the 5.725-GHz to 5.825-GHz band (also known as the Unlicensed National Information Infrastructure 3 [UNII3] band), antennas are limited to a power of 1 watt or 30dBm. Antenna gain for omnidirectional antennas is limited to 6dBi. Antennas with a gain higher than 23dBi must have power reduced 1 dB for every 1dB above 23dBi. The Cisco 1400 Bridge operates in the UNII3 band.

Antennas transmitting in the 2.4-GHz band are also limited to 1 watt with a maximum antenna gain of 6dBi. That said, there are also maximum values that depend on the type of system employednamely, point-to-point versus point-to-multipoint deployments:

• In point-to-point systems that use a directional antenna, for every decibel the transmitter is below 30dBm, the antenna can increase by 3dBi. For example, a 29dB transmitter can have a 9-dBi antenna; a 28-dB transmitter can have a 12-dBi antenna.

• In point-to-multipoint systems, the FCC has limited the maximum effective isotropic radiated power (EIRP) to 36dBm. For every dB that the transmitter is reduced, the antenna increases by 1dB.

Amplification

Simply put, unless an amplifier came as part of your wireless system, the FCC does not want you to use one. You are allowed to use only an amplifier that comes certified with your wireless system. Unless an amplifier was submitted for testing along with the radio and antenna, it cannot be sold in the United States and it cannot be sold separately.

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Bear in mind, if a system incorporates an amplifier, it must still adhere to the aforementioned regulations about power output and gain.