It will be quite a while before these SD feeds are shut down, as the new HD feeds will only provide signals to HD receivers and HD-DVRs. The SD signals will still be needed until D* changes its SD receivers over to MPG-4. What D* needs to do is build a receiver that receives a HD signal and converts it to a SD signal, if that is possible. That way they only need to transmit each station once. I guess they are waiting for the FCC to take away all current analog frequencies, then they will only have to worry about a single digital feed, for each channel. But if they eventually change their SD receivers over to MPG-4 compression, that will free up a lot of bandwidth.