I bought a ham radio antenna mounting kit for my car that includes ~16' of coax. One end has a trunk lip NMO antenna mount, the other end has a re-solderable PL-259.
I asked the sales person if it is best to shorten the coax after installation to only the length required to reach the radio transceiver and they said "I would just leave it, the length is already optimized for maximum efficiency at the factory".
I've heard of this before (mostly from CB Radio installers) but don't actually know if this is true or understand why/if there is an optimum feedline length for VHF/UHF FM use (vs Citizen's Band AM HF). I intend to be setup for both VHF/UHF but will operate primarily on 2M VHF and so any trade-offs should be optimized for the 2M band.
My SWR on 2M at my club's repeater frequency is 1.7. Would shortening the length change the SWR or only change the losses incurred due to the SWR?
I have a nice space in the trunk, normally used for a sub-woofer if you purchased an optional "premium stereo" with the car - in my case this space sits empty. I plan to keep the radio transceiver body in the trunk with the remote head unit up front. This would allow me to keep the antenna feedline shorter and make for an aesthetically clean installation. This would also allow the antenna feedline length to be something around 5-6ft if shortening it would be beneficial (although I could just coil up the unused ~10ft or so).