The new airwaves are particularly attractive because television signals are low-frequency waves, meaning they can travel farther, go more easily through walls, trees and other obstructions, and provide more reliable connections.

As with any developing technology, uncertainties remain. Urban areas, which have the most demand for the new airwaves, have less of them available because more local television stations are using available bands. Also, by making the airwaves available free, the F.C.C. is bypassing the possibility of using them to generate revenue, either through auctions or user fees.

The F.C.C. is virtually certain to approve the new rules at its Sept. 23 meeting, because it already has approved a similar set of rules, in November 2008. Those rules have never been in effect, however, because both supporters and opponents of the concept objected to some of the details.

Supporters challenged the F.C.C.’s decision to require new devices to include a feature that conducts an electronic search for airwaves that are not occupied, as well as to rely on a database of unused airwaves in choosing a frequency on which to transmit its signal. That belt-and-suspenders approach would have made devices more expensive because of the complicated engineering required.

The use of the white spaces was more generally opposed by a coalition of industries that included broadcasters, who feared that the new signals would interfere with their transmissions, and theater owners, sports arenas and churches, which make extensive use of wireless microphones that they, too, feared would be subject to interference.

Exactly how the F.C.C. has addressed those objections will not be known until the new rules are released at the Sept. 23 meeting. But people in the telecommunications industry who keep close tabs on the agency say they expect that the searching requirement will be abandoned, and that wireless microphones will be given certain transmission priorities.

Wireless networks that use the white-space signals are already being tested in several locations. Microsoft uses the signals in a wireless network that stretches over its corporate campus in Redmond, Wash.