You know I did think about the back to back balun transformer idea and we had several at the shop, but I metered the shield of F connector side and found that it was directly connected to one of the legs of the 300 ohm side, so I did not see where this would isolate the ground. Perhaps it was that particular model balun transformer was that way, so I'll try some others.

From my understanding of the construction of balun transformers (balanced to unbalanced 300 to 75 ohm) they were not a pure transformer that would give me the isolation I need but I could be wrong, its been a long time since I looked at it but I thought they were built like autoformers that don't give isolation.

Anyway I'll give this a try.

Let me know if you have any other ideas.
Jeff