Another option is to use a PC with HDMI output (Display port and DVI can be adapted to HDMI with a passive cable because the other 2 standards were based on DVI) and adapt HDMI to AV or RF...The nice thing about this method is any modern signal source device will have HDMI for the foreseeable future so this is relatively future proof.
Some older computers and graphics cards still support S-video...I built a new windows 10 machine in early 2019 and was able to make an OLD S-VIDEO capable graphics card work on it... Windows 7 would have supported the card better, but the motherboard didn't support windows 7(much to my dismay).
I wanted something slightly better than generic consumer HDMI adapters so I did this:
https://www.youtube.com/watch?v=hKjt3x4WtWU