When any cstandard aspect ratio is seen on a widescreen monitor without side bars, the channel has blown up the image and lopped off the top and bottom of the picture. The only way to see old shows in "full screen" is with bars.
And you only see "letterbox" bars when you view widescreen programs on a standard screen.
Antenna TV and the other oldies sub-channels have side bars when viewed on widescreen monitor. If you are not seeing side bars, probably you are watching on a standard screen.
And nobody has their "analog channel" on the air. The government shut down analog TV more than four years ago.