Custom video format for experimental television camera

[Beauregard42]

I had a system I was working on, using 255 lines at 40 fields per second. Interlaced, obviously, with 220-242 (min/max) lines of visible video information. Line rate is 5100Hz. No color system devised yet, so simple monochrome. HSync is 20uS, 0v. Black is 0.5v, and white is 1v. For vertical sync, it simply DC shifts down 0.5 volts for 6.5 - 27.5 lines, making the average about 0v, with Hsync being pushed to -0.5 volts. Total bandwidth is about 1.5 - 2MHz. Any tips/advice or modification ideas???

[Alex KL-1]

Intereting!
But, a compatible TV is needed, also. Or a converter, to see the results.

Back some almost 30 years I first read about the TV systems, I simply played with the calculator, and "devised" a system mixing the US and European high specs: 625 lines / 60Hz vertical scan rate ("625i/60"). H rate is (if I remember well) something in the vicinity of 18.750Hz. Some 9MHz of channel bandwidth are required (or are the video response?) (only a faint memory from the calculations from theses times; I never re-calculated it again). I not calculated the sync pulses duration, but black level was like the NTSC-J.

Fast forward and I understand the world wide adoption of systems having bandwidth like the M system and the European ones (relatively close each other, due to refresh rate differences), and why the audacious French 819i system failed to survive (hard to implement; expensive, especially for tube systems).

[old_tv_nut]

Originally Posted by Alex KL-1

Intereting!
... Some 9MHz of channel bandwidth are required (or are the video response?) ...

Would need about 4.5 MHz baseband for comparable vertical and horizontal resolution, so 9 MHz would be the RF bandwidth for double sideband modulation. Of course, you could extend the bandwidth and horizontal resolution in a proprietary system.

[old_tv_nut]

Originally Posted by Beauregard42

I had a system I was working on, using 255 lines at 40 fields per second. Interlaced, obviously, with 220-242 (min/max) lines of visible video information. Line rate is 5100Hz. No color system devised yet, so simple monochrome. HSync is 20uS, 0v. Black is 0.5v, and white is 1v. For vertical sync, it simply DC shifts down 0.5 volts for 6.5 - 27.5 lines, making the average about 0v, with Hsync being pushed to -0.5 volts. Total bandwidth is about 1.5 - 2MHz. Any tips/advice or modification ideas???

255 lines seems like it was chosen to fit an 8-bit counter. Was it?

[Beauregard42]

Originally Posted by old_tv_nut

255 lines seems like it was chosen to fit an 8-bit counter. Was it?

That wasn't my original intention, though... It could be made to fit an 8 bit counter, but I found that (roughly) halving the NTSC system gave me what I wanted without being unrecognizably low-res, and I was thinking about 256 lines, except it needed to be an odd number in order to be interlaced, so I just dropped it down one.

525 lines (NTSC) / 2 = 262.5

262.5 is a weird number. 256 is better.

256 won't interlace. Therefore 255.