Atari 2600 multicarts: picture problems?

[WaverBoy]

I've gotten two different Atari 2600 multicarts, one with 256 games on it from 4-Jays, and one with 128 games on it that I had custom-made. Both of them are made by different people, but they both have one annoying characteristic: the picture is riddled with weird texturing lines, showing up worse in some games than others, but all games on the cartridges have it. The problem looks identical in both multicarts. And, it's not my system or set-up, because it plays my original Atari cartridges just fine. For instance, the picture on my original cartridge of Donkey Kong looks great (well, as great as the old Atari RF can look). If I select it on either of the multicarts, it looks crappy. Anyone know what's causing this? Is it just the nature of the 2600 multicart beast, because so many games are crammed in there? I know nothing of such technical matters, but I do know that something's amiss. Help!

[Paul Slocum]

It's because those multicarts don't have RF shielding. No homebrewed carts do. The best solution I've found is to rearrange the cable going from the Atari to the TV. Often the cable is too long and a lot of it ends up coiled up near the Atari. Move the slack cable as far away from the Atari as possible.

 

-Paul

[WaverBoy]

I figured it was something along those lines. Why can't RF shielding be put in homebrew carts? What sort of shielding do the original Atari carts use?