Thank you, robinh and danke, ChrisS. It sounds like the 75 ohm resistor is required for at least some TVs. I'm considering making a product that generates video and I'm trying to figure out if I should include the 75 ohm resistor (at least as an optional component) and the diodes. I did experiments with diodes and they degraded picture some, and I was told that they were not strictly required. I'm just trying to design a device that would work on the most TVs possible.