The prototype device at the football game also failed to detect when wireless microphones were switched on, "an occurrence that takes place multiple times during any NFL game," Brunner added.

Google officials disputed Shure's description of the NFL test, saying the tests were successful. The problem at the football game was "more an issue with that specific device," said Richard Whitt, Google's Washington, D.C., telecom and media counsel. One device tested didn't sense wireless microphones because those microphones were using spectrum already occupied by digital TV signals, meaning the device found "false positives," he said.

"The device did not operate in terms of transmitting a signal, because it found that particular channel was occupied," Whitt said. "There would be zero chance of causing any interference to the signals, because in that situation, there certainly would not be a transmission of the signal in the first place."

During a Google press conference Monday, two men representing rural areas called on the FCC to approve the white spaces devices, saying large broadband providers have ignored their residents. Native Americans in Southern California do not have the same access to broadband as neighboring communities, said Matthew Rantanen, director of technology for Tribal Digital Village, based in San Diego.

"There's a serious broadband problem in rural America," added Wally Bowen, executive director of the nonprofit Mountain Area Information Network, based in Asheville, North Carolina.