I usually use
Chris White's web site for how to make cables.
Here is the trick:
- Do you know the frequency-response of the coax you used?
- Did you do a real good job of connecting the RCA plugs to the coax and are the RCA plugs designed for video signals (75 ohm impedence) or are they audio RCA plugs?
- Did you make sure all 3 wires are as close as possible to the same length?
These first 2 items are the real key to good video cables. Coax designed for the frequencies involved, RCA plugs as close as possible to 75 ohms (Canare), and proper connections.
The BEST way is to buy coax & connectors & tools all designed to work with each other. See the web site for exactly what to get to have this.
Even without all this, good parts and careful construction can give you a very good set of cables.