Originally posted by HD Rookie
Digital is not a prerequisite for HD. In fact, basic cable is not even a prerequisite for HD. Yes, analog is still functional when you upgrade to digital.
True... Unless you are one of those rare people who have the "broadcast-only" tier (for like $7/month) where the cable company installs a filter on the line limiting you the the first 12 or 20 channels, the high-frequency digital signals come through with all the analog channels.
Digital signals are typically sent on the high channels... At least on Comcast they are. My cable system translates the Chicago OTA signals to channels 112, 116 and 117. They are sent "in-the-clear," alongside the nearly 250+ digital subchannels spanning from channels 83-94 and 100-118, all of which are encrypted except for the DMX and Music Choice subchannels. FYI, the downlink for cable-internet service is interleaved into the same frequency range as these other digital services.
Some cable systems might actually stick the in-the-clear HD stations between two lower analog channels, too. My particular system doesn't do that, but for whatever reason, there are 6 encrypted subchannels way down on channel 25.