There are some channels on my cable service that seem to be rebroadcasts of these sub-channels. They are unwatchable. Sadly, PBS likes to make use of the sub-ch

There are some channels on my cable service that seem to be rebroadcasts of these sub-channels. They are unwatchable. Sadly, PBS likes to make use of the sub-channels to offer various educational program streams, but their main channel suffers for it. Fast motion degenerates into blocky artifacts quite often.