That plot works, but is only resolved to the block level.
Try the instruction here for a more accurate plot:
http://forum.tvfool.com/showthread.php?t=14508
What antenna do you have?
What direction is it pointed in?
Has anything in your setup changed?
Did you receive CITY-TV (RF Channel 44, Virtual 57.1) and then loose it? Or have you never received it?
What channels can you get? What channels do you want to get (in addition to CITY-TV)?