I have had the same problem in my house with a digital antenna - and yes, when you are holding the cable you are the antenna. With the Winegard, as someone has mentioned above, you need to aim that antenna to the direction where the most signals are coming from. It is a matter of aim, scan, see what results, aim again and scan again until you come to the correct direction. At that point you will not have to hold onto the cable to see a good picture. One way to shorten the process is with one of these -
http://roadtrek190popular.blogspot.com/2013/09/adding-digital-antenna-signal-finder.html