WTMJ 480p broadcast

[John Brundage]

I liked it when WTMJ broadcast a 480p signal on channel 4-2.  Typically, I prefer not to burn in the black bars on the side of my picture.  However, I have a Toshiba, and when the picture is broadcast in 1080i, I lose the ability to zoom in on the picture.  It really bugs me when there is a letterboxed show like E/R, and I'm unable to zoom in, and as a result get black bars not only on the side, but top and bottom as well.

By the way, several months ago, I was watching E/R with the black bars on all sides, and someone at the station must have thrown a switch, because all of a sudden, I was getting the full 16x9 screen.  I'm sure the station could send a standard definition signal out as a 16x9 picture if they could only remember to throw the switch.

Question: would sending out the 480p signal on 4-2 on a routine basis somehow degrade the HD signal on 4-1?  If not, I would encourage the station to resume the 480p channel.

[Pat]

Yes, it's my understanding that any sub-channels broadcast use up bandwidth that would otherwise be available for the others.  

What I'm not clear on, is whether there is any sort of dynamic on-the-fly sharing of bandwidth, such that if one channel happens to have an "easy" picture and another has a difficult one, can the second steal bandwidth from the first?  Or is the allocation fixed and immovable once set?