Random free HD cable in the 100+ channels?

How is it possible that I saw HD channels without cable or an antenna?

• Earlier today I hooked my cable wire up to my Plasma TV without using the cable box (which isn't HD anyway) and without an antenna. A few HD channels came through but not as many as it would be if I used an antenna. How is this possible? 1. I am 100% sure that the cable box was not connected to the TV and even if it was it's not an HD cable box. 2. I have no antenna on my roof, the side of the house or in the back of the house. The only antenna I have is a flat indoor one which is not connected to anything and is sitting in a closet.

• Answer:

  Cable TV company's often send the broadcast TV local stations signal onto the cable system in HD digital without scrambling them. This is called Clear QAM. All newer model TV sets have tuners built into them that can receive the clear QAM channels. Cable systems normally send only the "Main" broadcast signal in HD clear QAM the sub channels of the station are not in HD and may or may not be in even in the clear, usually they are but only in SD. A digital cable box is only needed IF the cable system scrambles the digital cable signals (Almost all do) so you need the box to de-scramble those signals.