Microsoft dropped off at the FCC a prototype white space device Dec. 11, designed to detect used frequencies in the DTV spectrum.

Microsoft had submitted a device that the FCC this summer found unreliable in detecting the signals. The software giant later claimed its device was defective.

Earlier this month, one of Microsoft’s partners in the White Space Coalition, Philips, submitted a pair of devices to the FCC for testing, and coalition partner Google showed the FCC data from its own tests.

The high-tech companies says the unused DTV channels known as white spaces are a fertile ground for new technologies including consumer mobile devices such as home networking and Web browsers, as well as for rural wireless broadband. Broadcasters, cable companies and wireless microphone makers fear that unlicensed mobile white space devices could interfere with broadcast DTV, cable operation, and wireless mic function.