In the US, the 2.4 GHz Wi-Fi radio spectrum is also allocated to amateur radio users. FCC Part 15 rules govern non-licenced operators (i.e. most Wi-Fi equipment users). Amateur operators retain what the FCC terms "primary status" on the band under a distinct set of rules (Part 97). Under Part 97, licensed amateur operators may construct their own equipment, use very high-gain antennas, and boost output power to 100 watts on frequencies covered by Wi-Fi channels 2-6. However, Part 97 rules mandate using only the minimum power necessary for communications, forbid obscuring the data, and require station identification every 10 minutes. Therefore, expensive automatic power-limiting circuitry is required to meet regulations, and the transmission of any encrypted data (for example https) is questionable.
In practice, microwave power amplifiers are expensive and decrease receive-sensitivity of link radios. On the other hand, the short wavelength at 2.4 GHz allows for simple construction of very high gain directional antennas. Although Part 15 rules forbid any modification of commercially constructed systems, amateur radio operators may modify commercial systems for optimized construction of long links, for example. Using only 200 mW link radios and two 24 dB gain antennas, an effective radiated power of many hundreds of watts in a very narrow beam may be used to construct reliable links of over 100 km with little radio frequency interference to other users.
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