Home solution for UHF TV booster

Hi,I know this is going to sound like a very lame question. In my country we only have 1 public channel. I recently discovered my television can pick up other channels, which have the same numbering as the cable channels. Certain channels I get great audio but poor visual,and on some channels I can get ok audio and visual. I don't have an outside antenna. Can anyone advise me on something I can build/obtian/modify to get better reception on these channels, I"d like to see channels 12-59 which are in uhf spectrum. A simple home recomendation would be nice.
Any help would be greatly appreciated.