The Federal Communications Commission said the prototype caused television interference in the 700 MHz spectrum as it sought a portion of the spectrum band that a television broadcaster doesn't use, PC World reported Tuesday.

The prototype was developed by Microsoft Corp. (NASDAQ:MSFT) and other companies under the name White Space Coalition in response to an FCC invitation last year to build the portable device sample. Other companies in the coalition include Dell Inc. (NASDAQ:DELL), Earthlink Inc. (NASDAQ:LNK), Hewlett-Packard Co. (NYSE:HPQ), Intel Corp. (NASDAQ:INTC) and Philips Electronics North America Corp.

The FCC previously said it would allow use of wireless devices in TV spectrum as long as they are fixed. But it later said it would consider allowing unlicensed portable devices to use the spectrum.

The FCC found the sample didn't not consistently sense or detect TV broadcast signals and sometimes caused broadcast interference.

The White Spaces Coalition said in a statement it was encouraged "that FCC engineers did not find fault with our operating parameters and remain confident unlicensed television spectrum can be used without interference."