I'm a little confused, do you currently have an antenna connected to a Tablo? If so then there are a number of things that could be effecting your reception beyond the RG-59 cable.
How far are you from the TV towers in your area? What antenna do you have & where is it mounted? There are sites on the internet that will locate the TV towers in your area & where they are from you. This will help you know which antenna you need & where to mount it & which direction to point it. If you are not capable of mounting an antenna & running the required coax through your house, you should be able to find a general Handy-Man in your area that can handle this sort of work.