Question about my tv tuner?

i have the Hauppauge WinTV-HVR-1600. i have a rooftop antenna and i get digital tv with the tuner. so no more static. the problem is, if the tv signal is weak the video and audio get jerky. i want to buy something to amplify the signal. can you find me somethings that can help? either for the rooftop antenna or a little one before the cable goes into the computer