FCC Amends Part 15 Rules to Allow Higher-Power Devices at 24 GHz

NEWINGTON, CT, Dec 18, 2001--Despite objections from the ARRL, the FCC has announced plans to amend its Part 15 rules to allow fixed point-to-point transmitters in the 24.05 to 24.25 GHz band to operate at field strengths of up to 2500 mV per meter. Among other safeguards against interference, the FCC will require devices operating at these higher field strengths--10 times the level currently permitted--to use highly directional antennas. Amateur Radio is primary at 24.0 to 24.05 GHz and secondary on the rest of the band. The AO-40 satellite includes beacon, digital and analog transmitters in the vicinity of 24.048 GHz

"This band has accommodated unlicensed transmissions, government radar and amateur facilities with no major conflicts," the FCC said. "By allowing a greater variety of systems to occupy the band, we will provide the opportunity for innovative products and services to be made available to the American public as quickly as demand dictates. The FCC said those "innovative products and services" include managing network traffic on a high-speed wireless Internet service or connecting a multi-building intra-office network.

The FCC first proposed permitting the Part 15 devices at the elevated field strengths in 1998, in response to a Petition for Rule Making from Sierra Digital Communications Inc. Sierra had requested that its proposal be authorized to include a portion of the 24.0 to 24.05 MHz segment, but ARRL had argued that such a move would adversely affect amateur operations there, and the FCC agreed. The FCC finally acted in the three-year-old proceeding, ET Docket 98-156, on December 11 in a Report and Order that closely mimics its earlier Notice of Proposed Rule Making.

Noting that Part 15 devices operate in a non-interference basis to licensed services and must accept interference from licensed services, the FCC said it was requiring directional antennas with gains of at least 33 dBi to minimize interference potential. The FCC also imposed more stringent frequency stability and spurious emissions requirements than initially proposed to help reduce interference potential.

The FCC said it disagreed with ARRL that permitting Part 15 devices at the higher field strengths would increase the risk of interference to amateur operations in the 24.05 to 24.25 GHz segment. "The use of a directional antenna will change the shape of the radiated radio frequency field but not the amount of geographic area contained in that field," the FCC said. The Commission said that Part 15 field disturbance sensors have operated in the band at 2500 mV/m field strengths "for years with no adverse affects to other users in the band, including amateur operations."

The ARRL pointed out that the FCC had earlier denied a request to allow low-power fixed systems in the 24.04-24.25 GHz band, but the FCC said that Sierra's application would involve much lower power levels than the earlier proposal, not to mention the use of highly directional antennas. The FCC also turned down an ARRL request that manufacturers maintain detailed records of unlicensed transmitter installations that employ the expanded Part 15 operating parameters and supply it to ARRL for coordination purposes.

The FCC took issue with ARRL's assertion that the FCC should acknowledge that Part 15 devices are only allowed under the Communications Act when they pose no interference potential to licensed services. Calling the ARRL interpretation "overly conservative," the FCC said Part 15 rules appropriately provide for unlicensed devices to share spectrum with licensed services and provide adequate protection to licensed services if interference does occur.

The entire 24.0-24.25 GHz band is allocated for use by Industrial, Scientific and Medical (ISM) equipment. In addition to Amateur Radio, the 24.05-24.25 segment is allocated on a secondary basis for radiolocation in the Private Land Mobile Radio Services and for Earth-exploration satellites. The band is adjacent to frequencies authorized for satellite Earth exploration and for radio astronomy and the Digital Electronic Message Service (DEMS).

The FCC Order in ET Docket 98-156 is available on the ARRL Web Site.

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