Cant tune DTV to Ch5?

I have an LG plasma with integral freeview downstairs which receives all channels no problem. I also have a small Matsui lcd in the bedroom which only receives a few of the digital channels (it is on a different arial) So, assuming the obvious, I plugged the lcd in downstairs so I could at least store the channels & could then adjust the arial, however, it still only picks up the same few channels as before. I am missing Ch5, USA & Fiver, along with abc1 & others - anyone any ideas please?