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Operating an unlicensed radio carries with it the obvious risk of interference from other unlicensed operators in close geographic proximity to your sites. Of course, there's no absolute assurance that interference will not take place on licensed frequencies, but in those cases, you at least have legal recourse. Vendors vary somewhat in how they take advantage of available bandwidth and deal with interference. BreezeCom's BreezeLink, for example, is based on a frequency-hopping spread-spectrum (FHSS) design that uses the entire 2.4-GHz spectrum. The other vendors use direct-sequence signaling. P-Com uses 95 MHz in the 5.8-GHz band, Adtran uses the entire 2.4-GHz band, while GWM and Wave Wireless both provide multiple channels at 5.8 GHz. Most of the vendors recommend the use of high-gain directional antennas with their systems. A 5.8-GHz four-foot parabolic antenna provides 35 dB of gain and has a beam width of three degrees. With such a narrow beam, the probability of interference is quite low, and even if it does occur, there are strategies for correcting the problem, including using alternate channels in some cases or reversing the polarization of antennas.

None of the vendors manufactures its own antenna. Some, including P-Com, offer packages that include radios, cables and antennas--everything you need to install a link. Other vendors offer antenna and cabling packages or provide recommendations for products from third parties. The cost of antennas ranges from about $500 for a two-foot antenna with 28.5 dB of gain and a six-degree beam width to $2,500 for an eight-foot antenna with 41 dB of gain and a one-and-a-half-degree beam width.