I recently got comcast digital cable with HDTV programming. I have a 32 inch 4/3 Hitachi Ultravision HDTV. Of the four HDTV stations comcast delivers- two of them - KQED (and one other whose call letters I can't recall)- are displayed by my 4/3 screen in expected letter box form. However on the other two channels - ABC and I believe CBS - I get bars on all four sides of the screen (i.e both letter boxed and window boxed) which in essence is diplaying HDTV in 4/3 format but just shrinking the former 32 inch screen down to around a 25-26 inch screen. Why is this and how can I fix it.
I just got my hands on an RCA DTC-100 and I noticed the same thing on some of the channels. It was kind of funny actually. Here's why it happens though...
I have a Proscan (RCA) 4:3 big screen. Somewhere in the DCT-100 menu (and probably in your cable receiver) there is an option to show HD info in 16:9 or 4:3. The 4:3 setting will cause the bars at the top and bottom for wide screen pictures for widescreen date. The top two (True) HDTV resolutions are widescreen only.
Now, some TV station simply upconvert their regular 480i info to HD, but because the original picture was 4:3 THEY ADD BARS TO THE SIDES so that the picture doesn't look squashed. It would be better if they simply sent you a 4:3 480P signal, but they don't.
You may be able to get around this by trying various combinations of "fill" and aspect ratio in your TV and cable box.