Steve, ever hear that mounting an antenna in the centre of the roof, or trunk lid works better as a nondirectional antenna?
I've heard about CB.
You bet. My transmitted signal would be closer to omnidirectional if the antenna was in the centre of the roof. There are a couple of things that prevented me from drilling a hole however. The biggest wasn't cosmetic. I want to see what is under the headliner and keep the antenna away from the vehicle electronics.
Modern cars and trucks have a lot of electronics packed into a small space. I am unsure if there would be any interaction, so the best option was to put the antenna where it will cause the least harm.
The other thing is, this radio is an FM transceiver. The signal has to reach a rebroadcasting station (repeater) so that my signal can be boosted and rebroadcast.
Unlike ssb or AM, one only needs enough power to reach the repeater and not bring in any noise. This is referred to as "full quieting".
Most FM transmitters have several power levels. I have never needed more than 25 watts out, even though my radios have a 50 watts max. output capability.
So, where I live at least, as long as I can hit the repeater at full quieting, the antenna radiation doesn't need to be the most efficient.
My apologies for the long winded response.