boosting the video signal

[Jeff-20]

I just got a little B&W 4 inch mini tv from a thrift store. It has a 1/8 inch antenna jack. I wanted to hook up the VIC, but the signal seems too weak. I'll put up a picture when I can. How can I boost the signal? When I hook up other systems (Genesis), I get an image albeit a little static-y. How can I make it stronger?

EDIT:
It now works. You know how it takes a second or two for the signal to become clear on the screen? The little tv take about 165 seconds! (I only timed it once). The picture is very good after 2 and a half minutes...