In the past, when I listened predominantly to AM/FM on my vehicle's radio, I made a dramatic improvement in my station reception by installing a Fuba Betaflex-D antenna. This antenna can be found from various sources on the internet. It may be a direct replacement for the factory Prius antenna, but you will have to provide a 12V source for the antenna's amplifier. I usually placed a switch inline on the power source so the antenna can be shut off when in high-gain areas.
