I Started this monitor in 2017 and experimented in higher line rates other than standard NBTV 32 line 12.5 rates
Did a fair bit of work with this little CRT build is here
http://www.taswegian.com/NBTV/forum/viewforum.php?f=31
We have FreeNBTV software can use any thing you want line rates up to 240 line found here
http://www.taswegian.com/NBTV/forum/...=2458&start=45
Well only limited to the bandwidth of your sound card so that limits you to the video quality not the line frame rates ...so what i did to keep the video Quality with the bandwidth possible for the highest line rate was drop the frame rate below is 240 line 2 hz image is still viewable sort of a cross between SSTV and NBTV .
I call it SNBTV ; ) slow NBTV ! short you tube video below and camera results slow enough for the cameras shutter to pick up all the image .
https://www.youtube.com/watch?v=4qoeoWDusQI