Pal system B uses inverted modulation. Has to do 1- sample. It is referenced in the system B wiki article, but found it looking on hackaday gnuradio project. https://en.wikipedia.org/wiki/CCIR_System_B
http://www.batsocks.co.uk/readme/video_timing.htm http://blog.retroleum.co.uk/electronics-articles/pal-tv-timing-and-voltages/
Teletext editor https://github.com/rawles/edit.tf
https://archive.teletextarchaeologist.org/
https://teletext.wiki.zxnet.co.uk/wiki/T42_packet_stream
Export t42 from this. Can be modulated directly. https://zxnet.co.uk/teletext/editor