The Atari Jaguar will output RGB natively and only an RGB cable is needed. Please scroll down for more information.
RGB Cables (select csync from the drop-down menu):
Atari Jaguar RGB SCART cable
If you’d like, you can try to make your own RGB cable. First, get a 24-pin dual-edge connector, (.100 DIP). Digikey has them here. Then wire RGB to pins 4B, 7A, 5A (respectively), wire RGB ground to pin 10B and csync to pin 5B. There doesn’t seem to be any components necessary on the RGB lines (I think!), but a 680 ohm, 1/4 watt resistor and a 220uF/16v capacitor are required on the csync output. Also, don’t share video ground with audio: Make sure to wire audio ground to pin 2A. Here’s a diagram from Atarimax.com:
Tempest Controller Mod
There’s a cool mod that allows you to install a spinner into your Jaguar controller, so you can play Tempest the way it was meant to be played. Click the link above for more information.