Fuba Antenna Question

  I recently picked up a Fuba antenna off of ebay. I installed it, it looks great, and gets great recption. Only at home. I live in the foothills of San Jose, California facing the "Silicon Valley". As soon as I drive down the hill, I loose the radio stations. Could the fact that I'm installing it on a car with a fiberglass roof cause this problem? I am putting it on a 1993 Saturn SW2. They have plastic body panels and a fiber glass roof/lift gate. Also I had to use an extension to get the cable to reach my headunit. I wrapped up the excess cable and put it under the rear seat. Could this cause problems? Could too long of an extension cable cause problems?