I did this test using the signal generator and the rf output of a vcr. I'll show you pictures of the signal generator because it is much easier to photograph the phenomenon I have tried to describe.
The picture above is with the generator directly coupled to the rf input on channel 6. The pattern is vertical lines. You can see that the vertical lines make up what I was calling the "bottom" picture. The three horizontal lines along with the bigger bright vertical line make up the "top" picture. Feeding the signal with the generator makes the bright vertical white line stationary and straight, thereby easier to see. You can see that there is also retrace lines through the picture but that is another fight for another day.
The second picture is with the output of the generator decoupled from the antenna input but still near the input terminals. You can see the signal go down and a bit of static starts to appear. The bright white vertical line starts to curve and make an S pattern. The line has this shape and sways when the set has a moving video signal.
The last image is with the lead from the generator decoupled and out of close proximity to the set.