Take a look what i just found at amazon:
Their description:
Product Description
There is nothing worse than having a great TV to watch your favorite programs, while having a grainy or pixilated (digital cable) picture. Motorola BDA amplifiers give your TV signal a boost while maintaining full compatibility with all of your cable services. Simply install the BDA-S4 where your cable or antenna comes into your house and begin enjoying a better picture, faster downloads, and a more reliable HD or Digital TV signal. With a name like Motorola, how ca… More >>
Go & get it here - i can recommend it:
Motorola Signal Booster 4-Port BDA-S4 Cable Modem TV HDTV Amplifier