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Spring 2003 Issue |
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On Amateur Radio
Use of IEEE 802.11b The following white paper on the use of IEEE 802.11b protocol has been published on the ARRL website. It is reprinted here courtesy of the authors.
By Paul L. Rinaldo, W4RI
John J. Champa, K8OCL |
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The 2400–2450 MHz band is not only an amateur allocation but also is used by other services. Primarily, it is an industrial, scientific, and medical (ISM) band with a center frequency of 2450 MHz. Other users of the band must accept any interference from ISM emitters. The amateur service has an allocation in this band that differs somewhat in various countries. In the United States, however, the amateur service has a secondary allocation in the 2400–2402 MHz segment, primary in 2402–2417 MHz, and secondary at 2417–2450 MHz. This band (actually a larger band of 2400–2483.5 MHz) is used by a number of unlicensed low-power devices, such as cordless telephones and radio local area networks (RLANs), which include IEEE 802.11b and Bluetooth. Quite often, the trade press mischaracterizes this band as “unlicensed spectrum,” indicating perhaps that they are not aware of the amateur primary or secondary allocations. One other thing about amateur allocation status is that on petition from ARRL, the FCC has issued a Notice of Proposed Rule Making to upgrade the band 2400–2402 MHz to primary status.
This jumble of allocations and uses can be
viewed as a glass half empty or half full. One view is that the FCC has
loaded this band with so many applications as to make amateur operation
very difficult. There are growing anecdotal stories that amateur systems,
particularly amateur television repeaters operating in this band, are
experiencing harmful interference from IEEE 802.11b devices. There is
growing use of 802.11b in building and campus RLANs. The general
experience is that RLANs inside buildings usually do not radiate much
energy outside because of outer-wall attenuation. Even windows can
attenuate the signal through application of sun-shielding film.
The main interference from 802.11b to amateur
systems seems to be the outside RLAN access points (APs). Most operate
within the FCC Part 15 Rules, which may or may not be a problem to amateur
systems, depending upon proximity, line-of-sight, and other factors. Those
close by, perhaps with directional antennas bore-sighted toward an amateur
station, are likely to be a problem. In addition, there are an increasing
number of APs operating outside the Rules. IEEE 802.11b presents the amateur radio community with an opportunity to use the inexpensive RLAN cards for high-speed multimedia applications, including streaming television. While most prices presently hover around $100, some are available at about half that price. The APs, however, are more expensive by virtue of lower sales volumes, but they are available for several hundred dollars.
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