If you connected your DISH box with the RF antenna output to the TV antenna input you would need to select cable as you antenna type and run a channel scan with the box connected and on.
Your old TV may have been connected this way but you will get a better picture by using the HDMI or any other video and audio connection you DISH box has and selecting that input. If you don't have an HD box I would highly suggest you get one from DISH. The picture will be much much better.