Approximately 7 percent of broadcast stations making the switch from analog to digital signals next year will experience a loss of service coverage, known as the "digital cliff," according to a Tuesday report from the Federal Communications Commission.

The 7 percent of the affected stations are expected to lose about 2 percent of their audience because of the phenomenon, which includes both changes in the coverage area as well as technical issues with the digital signal, the FCC said.

That covers 123 of the 1,749 stations that will be making the switch. Congress has ordered TV broadcasters to switch from analog to digital signals by February 17, 2009 in order to free up spectrum for public safety use. After that deadline, consumers will have to swap their analog TVs for digital sets, subscribe to cable, or attach a digital converter box to their analog televisions in order to receive a signal.

"Although the Commission tried to maximize the ability of TV stations to replicate their analog coverage area as closely as possible, TV station were not required to do so," according to the report.

As a result, some TV viewers might experience a change in their coverage areas. Approximately 89 percent - or 1,553 stations - will gain channels, but that 7 percent, mostly in rural areas, could see certain channels drop off that digital cliff, the FCC found.

Why? With analog sets, a TV will become snowy or display static as the reception fades, but on digital TV sets, the screen simply goes black. This can occur for a number of technical reasons: a channel change from VHF to UHF; a station that did not maximize of replicate analog service area; a station that relocated its transmitter; or a station changed its antenna pattern.

Stations expected to lose service have several options, including the use of: "translator" or fill-in stations that operate on a different channel); the use of another station's sub-channel to be transmitted via multicasting; maximizing the station's power; changing the station's channel; or changing the antenna pattern.

To prevent further disruption, the FCC announced Tuesday that it will look into creating a new "replacement" DTV translator service that will let full-service TV stations provide service to areas that are victims of the digital cliff. Given that FCC rulemaking is not usually a swift process, broadcasters will be able to apply for special temporary authority to use these translators while the rulemaking is pending.

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