I just put my Diamond-D150 discone antenna inside the roof with RG-58 cable and the reception wasnt good at all but i changed the coax Belden-9913 and the reception was excellent.
You can buy the best antenna out there but if you cut corners with coax or use alot of connectors or fail to use a good ground your getting no where. Its good to see so many posts lately about the subject it really is a great accomplishment when it all comes together and you reap the benifits.......Good Scannin Hoser