Need Advice on Antenna

I recently installed a Uniden Bearcat police scanner in my truck. I'm running a nmo mount larsen triband antenna on the roof. The antenna doesn't seem to be picking up much like it was when it was just mounted in my home on the antenna that came with it. I primarily listen to frequencies 148-156. I live in a very hilly area with a lot of uneven terrain. What antenna do you guys recommend?

 

Bump

 

I assume you got better reception when it was out of the truck?

What frequency ranges are on the tribander antenna? If you are only going to receive on that frequency range, then a single band VHF antenna would work well. I have a Larson 5/8 wave (on 2meters) than be cut/tuned for most of the VHF high band. I used it for years on 2 meter amateur but cut it down for 150 VHF public service transceiver use the model is NMO-150B. Cut mine to 155 Mhz or so.

Your terrain could be the only issue. Hard to tell without more info.