Originally posted by Shadow=ASP=:
Sorry, I forgot about the NTSC system.
btw regular NTSC requires a little more bandwidth than 29.9KHz actually. Closer to 31.something KHz (my old CRT projector support up to 30.5KHz and it isnt enough). Some bandwidth is also used for refreshing horizontal too. But close enough.
Anyway, the LCD monitors can change refreshrates, they just cant change resolution.
You're talking about horizontal refresh rate (usually in kHz), we were talking about vertical refresh rate (usually in Hz).
The NTSC frame rate is 29.97 interlaced frames per second! This yields an effective framereate of 59.94 Hz (meaning 59.94 full frames per second)
This is the so-called vertical refresh
rate and tells how often the cathode ray is moved from the top to the bottom of the screen, thus telling how many pictures per second are generated.
The vertical refresh rate
tells how often the cathode ray moves across the screen from left to right.
If you know the horizontal refresh rate you can calculate the vertical refresh rate easily.
30.5 KHz horizontal refresh rate.
If your projector could display 1024x768 pixels, then the maximum framerate possible would be:
Horiz. rate/horiz. lines x 0.95 (because the ray needs about 5% of the time to travel back to the opposite side of the screen in the next line to display.
30500/768x0.95= 37.728 Hz
But your projector is a "near" NTSC projector, I think
Take the 480 lines of an NTSC frame:
30500/480x.95= 60.365 Hz Voilá!
A complete NTSC frame has 525 lines, the difference is used for synch, captioning etc. So your projector can't obviously show NTSC frames but maybe computer frames (640x480) at 60 Hz
Now you know why good CRT monitors have a horizontal
refresh rate of more than 100 kHz.
You need this especially for higher resolutions.
Speaking of TFT's changing the refresh rate:
My TFT supports 59-61 Hz only.
TFT's that can show both refresh rates usually can't display refresh rates other than 60 Hz and 75 Hz, with a small margin of course.
Apart from that TFT's neither change the refresh rate nor the physical! resolution. CRT'S can change both, refresh rate and resolution (actually the aperture mask is not changeable too).
You were talking about bandwidth (meaning horizontal refresh rate actually), that's something different from both vertical and horizontal refresh rate.
The NTSC tv channel bandwidth lies at 6 MHz. More information about tv signal bandwidth, sidebands etc. is available at wikipedia.