Wavy lines are typically caused by 60 Hz interference, usually a result of ground loops i.e, ground current flowing through the shield of the RG6 (or any other coaxial cable) and modulating the video carrier. Normally there shouldn’t be any grounds from the shield of the coaxial cable to the frame, or definitely only at one end. However, I suspect that both TV set and the DTV receiver both have ground connections through the A/C plug, effectively creating a ground loop if there is any ground potential difference between the front and rear of the coach. So, now what?
First try running a coaxial cable through the RV (across the floor) between the DTV receiver and the TV, assuming you mean 19” TV and not a 19” CRT such as a monitor. That probably won’t correct the problem, but if it does, check for grounding of the coaxial cable shield to the coach frame. Assuming this test fails to eliminate the wavy lines, run an extension cord from the front TV to the same receptacle used by the DTV receive in the bedroom. If the wavy lines disappear, you definitely have a ground loop problem, in other words, current flowing through the shield of the coaxial cable. If either the first of second test corrects the problem, you can then move on to the solution, which is the subject of another missive.
