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A prototype wireless device intended to share radio spectrum with television channels was malfunctioning when staff at the U.S. Federal Communications Commission tested it, Microsoft Corp. said Monday.

The FCC on July 31 said a wireless prototype submitted by Microsoft and other members of the White Spaces Coalition interfered with cable television channels and therefore would not be licensed for use. The White Spaces Coalition, including Google Inc., Dell Inc., Intel Corp. and other tech vendors, wants the FCC to approve wireless devices that operate in the so-called spectrum white spaces between TV channels.

Microsoft, in a letter to the FCC Monday, said the scanner in of one two prototypes submitted was damaged and "operated at a severely degraded level." The scanner in the wireless device is supposed to sniff for broadcasts in spectrum before transmitting in the band and switch to another band if the first one is occupied. The FCC found that the prototype did not consistently detect TV broadcast signals and could cause interference.

Microsoft had tested the prototype and found that it operated within FCC specifications, wrote Ed Thomas, a consultant for the White Spaces Coalition and a former chief of the FCC's Office of Engineering and Technology. "The damaged scanner accounted for the entire discrepancy between the Microsoft and the FCC bench test data," Thomas said in a letter from the coalition's law firm, Harris, Wiltshire & Grannis LLP.

Microsoft, in a statement, said it hopes the FCC will move forward with the approval of white spaces devices. The company is "confident" that unused channels in the TV spectrum band "can successfully be used" and not cause interference to incumbent licensees, it said.

The FCC found that a second prototype device submitted by Philips Electronics North America Corp. could detect both digital television and wireless microphone signals in the laboratory, Microsoft noted.

Television broadcasters have questioned whether dozens of new wireless devices operating in prime TV spectrum will interfere with signals. The National Association of Broadcasters and the Association for Maximum Service Television in comments filed with the FCC in March saying wireless microphone makers and public safety officials have "identified serious interference concerns" with unlicensed devices operating between TV channels 2 and 51.

The two groups said unlicensed advocates "provide little or no technical data to support their positions," while broadcasters have provided measured test data. "All of the measurement data submitted in the records support the [broadcasters'] technical positions," the groups wrote in their FCC filing.