Jailbars picture query

[Spector]

I get these thin, moving parallel lines on my Colecovision screen, like shadows, often referred to as "jailbars", and I'm wondering if there is a way to get rid of them. Would better shielded cabling make a difference? 

[Ikrananka]

What video output are you using, is it the original RF output or from a video mod?

[Spector]

6 hours ago, Ikrananka said:

What video output are you using, is it the original RF output or from a video mod?

It's from a video mod - composite. And it's a great mod too. The colours are bright and the picture is sharp. The only problem is these bloody jailbars! 

[Ikrananka]

Are you able to test the RF output to see if the jailbars are also visible there?

[Spector]

4 minutes ago, Ikrananka said:

Are you able to test the RF output to see if the jailbars are also visible there?

I can't do that because I'm in the UK and this is an American model: only a composite NTSC signal can be converted, not rf. Do you think interference is causing the lines on the screen, or is it something else? 

[ChildOfCv]

9 hours ago, Spector said:

I can't do that because I'm in the UK and this is an American model: only a composite NTSC signal can be converted, not rf. Do you think interference is causing the lines on the screen, or is it something else? 

One way to test that out would be to move the mod board around and see if it affects the picture.  You may in fact be too close to a clock line or other regularly occurring signal and be catching radiated interference from it.