I've been struggling to get rid of horizontal bands of video interference which rise vertically up the screen. I realized today that they only appear, and move up the screen, when the Tx is powered up. It is an old Crossfire Module in a new Boxer. I recently upgraded this 5" quad with a Speedybee F405 FC and RDQ Mach 3 VTX. Camera is an old Foxeer. Rx is a Crossfire Nano. I have a cap at the XT60.
I've powered the camera from the VTX as well as from the FC pads, no change.
I have tried several different antennas, no change.
Motors running or not doesn't matter.
Power output or channel frequency changes don't matter.
In close proximity or while flying doesn't matter.
Whether the quad is fully assembled or spread out like a dissected frog on my bench doesn't matter.
But when I turn the Tx on and off with the quad powered up the bands appear and disappear.
Any ideas?

Video interference being caused by a TBS Crossfire receiver was covered by JB a couple of years ago. You might want to have a watch of his video on that at the link below...

Thanks Snow! Once again, if I had known what the correct question was I might have found this on my own, your encyclopedic knowledge saved the day. JB's video shot and explanation of the cause was exactly what I had going on in my quad. In my case I had originally run the 3 camera wires to three adjacent pads on the FC. But I did not wind them. I never have in any of my builds so I've been lucky. Because of the interference I had moved the camera's power and ground to the VTX but this did not solve the problem. Putting those three wires back together and winding them tightly solved the problem. Interference banished!
I mentioned in another post that I had installed the FC backwards because the wires hanging off the old ESC were too short. That was what necessitated the long runs from back to front to the camera which were too close to the antenna length, in length. If I had oriented the board as the manufacturer designed it and run short wires directly to the camera, or if I had wound the camera wires tightly in my original build, I probably would not have had to go on this "wild goose chase".

Had a great time flying with decent video yesterday