I'm guessing that the original loop doesn't like the extra 600-700 feet of cable tied to it. It gives you a chance for an extra antenna. Try connecting only the remote building to the line and listen for background noise. If it goes away, your solution might be a small phone system where you are feeding an extension to the remote building.

For fun, you could do some research on bridge lifters here

In the C.O. days, we used to use them on party lines. It was great for hanging 4 separate cables on the same line, or an answering service to the customer's main number. Bridge lifters are probably made of unobtainium, but somewhere I have a single unit that weighs a lot and does such a feature. It may show up in the next 2 months.


Carl