Shielded 300 ohm twinlead used to be sold by radio shack. I used it for many years and it did a super job of eliminating noise from ignition of nearby vehicles. This was in a fringe reception area, and I wanted to avoid any loss of signal due to a 300/75 transformer. The shield was left floating: not grounded at either end. Modern FM tuners take a 75 ohm antenna connection, so you are going to need a transformer anyway. I have recently installed a small lower down FM antenna, with a mast mounted RF amplifier and 75 ohm coax, and it works as well or better that the old antenna with the shielded 300 ohm twinlead..
