You may need to re-terminate the coax, or add an amplifier. With digital signals, it either works or doesn't. If the signal is low, the channel is just unavailable, rather than "snowy" .
The amplifier kanewolf suggests should solve you problem (or a better aerial). If you use RF splitters get good ones too. The signal will get lower the further away and the more splits it has to travel through to get to the TV. Different TVs have different tuners in them and this affects the performance with weak signals quite a bit.