The circuit needs that the VGA card sends out the video signal the the RGB format compatible with PAL or NTSC standard video timings. This is accomplished with right VGA to TV driver.This circuit is based on AD722 IC from Analog Devices. The AD722 is a low cost RGB to NTSC/PAL Encoder that converts red, green and blue color component signals into their corresponding luminance (baseband amplitude) and chrominance (subcarrier amplitude and phase) signals in accordance with either NTSC or PAL standards. These two outputs are also combined to provide composite video output. All the outputs can drive standard 75 ohm terminated video cables directly without extra amplifiers. The chip is a very compact solution, because operates from a single +5 V supply and it need no external delay lines or filters.

• Power supply: Regulated +5V power supply, needs less than 300 mA
• Video input: R G B + HSYNC + VSYNC from VGA card, refresh rate compatible to PAL or NTSC standards
• Video outputs: Composite video and S-video (Y/C)
• Video standards supported: PAL B,G,H and NTSC M

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This is RGB To Monochrome converter by using Matches impedance of PC to a B/W or CCTV monitor technic.You can get away with running a monochrome monitor on GREEN, but this looks real crappy when viewing color images. These simple resistor networks allow you to display R+G+B on a B/W or CCTV monitor without ghosting. Be shure to set your video card for 60Hz interlaced. Most video cards do give you Csync out on H. You can also run an OLD monochrome EGA or VGA monitor like this, but be shure to hook up the Vsync. This will not work on TTL monitors. source