The typical approach to solve this issue, Is to run your Heavy LMR400 to just below the rotator, and then Transition to a short piece (less than 10 Ft) of a excellent Grade of RG-8 Foam Coax to span across the Rotation Area of the Tower. The addition of just 10 Ft of Higher loss coax, will not introduce much of a actual Resistance Loss, to the Total Antenna System. Also make the Transition cable using the least Lossy Connectors for that Frequency Spectrum used on the Antenna. Type N, if your using more than 100 Watts, and BNC/TNC if your below 100 Watts. When I had a BIG Tower with Multiple Antennas, All the main runs from the shack were done with Beldon 9913 (Poor Man's Heliax) for HF Antennas, and 1/2" Heliax for VHF Antennas, and 7/8" Heliax for UHF Antennas. They all terminated on a galvanized Steel Plate, that was drilled and taped to accept Chassis Mount type N Female Connectors. Then all the coax runs, across the rotator section, were made with 6 Feet of RB-8/U Foam Coax to a second galvanized Steel Plate that terminated with duplicate, short runs, of the same Cable Types, that were used with each Main Run, from this second Plate and Chassis Mount Connectors, up to the individual Antennas. The six foot sections of RG-8/U Foam were just used to bridge the Rotator area on the tower. Just Say'en... YMMV...