Information found at FCC's Digital Transition Web Site:
http://www.dtv.gov
IS MY T.V. DIGITAL?
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All Digital T.V. sets have labels or markings that may contain the words "Integrated Digital Tuner," "Digital Tuner Built-In," "Digital Receiver," "Digital Tuner," "DTV," "ATSC," or "HDTV."
The Commission's digital tuner rule specifies that as of March 1, 2007, all new TV sets must include digital tuners.
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http://www.dtv.gov/consumercorner_2.html#faq11
Can Cable Companies Make it Mandatory to Subscribe?
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If a cable company makes the business decision to go all-digital, it must ensure that its analog customers can continue to watch their local broadcast stations. This may require some customers to get a set-top box. Contact your cable company to ask if a set-top box will be needed, when it will be needed, and if there will be a cost. Any related costs will be determined by the cable company.
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http://www.dtv.gov/consumercorner_3.html#faq1