Phil,
I am guessing that your R29 Classic is built very similar to my 2014 R31S. I had trouble picking up any broadcast signal with either TV just as you describe. On a trip just a few weeks prior to noticing the reception problem, reception was okay but somewhat degraded. Then shortly afterwards there was no reception. One of the Ranger Tugs factory technicians told me it might be the splitter which he thought was behind the wooden box on the starboard wall just behind the helm seat. This box runs from the counter top to the ceiling and contains several types of wiring.
Not wanting to tear that box apart, I simply removed the coax connector attached to the antenna on the roof to inspect it. What I found was a heavily corroded center electrode in the connector. There was not enough slack to cut the connector off and replace, so I used my knife to scrape the electrode and some sand paper to smooth it up. After re-assembly, TV reception was perfect. I also put lots of dielectric grease in the connector to hopefully avoid such trouble in the future.
To diagnose your problem, you might buy a section of coax and temporarily directly connect it to a TV and run the coax out a window and up to the antenna temporarily replacing the factory installed coax. Or, you could just do what I did to see if that solves the problem.