Hi Darren,
You are using the ADV7280-M evaluation board correct?
Could you check that the NTSC source is ok?
- Please feed the CVBS video directly to a television and see if you see the same issue.
- Could you please take an oscilloscope plot of the CVBS input to the ADV7280-M evaluation board.
- Are you using a shielded cable to transmit CVBS video over.
- Is the cable shield grounded at both ends?
Note that single-ended CVBS is susceptible to noise sources. Shielded cables are required to protect single-ended CVBS signals from noise sources.
Differential CVBS is a method of transmitting analog video without the need for shielded cables. The ADV7280-M does not directly support differential CVBS ( an external OMAMP circuit would be needed). The ADV7281-M, ADV7281-MA and ADV7282-M parts do support differential CVBS. More information on differential CVBS can be found by reading the ADV728x hardware manual.
http://www.analog.com/static/imported-files/user_guides/ADV7280_7281_7282_7283_UG-637.pdf
Regards,
Robert Hinchy