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CRT Primer

Updated: January 2008

Index: 


Hooking it all up (Video Signal Types)


 



I've had a lot of inquiries about the various signal types that exist (including newer digital HDMI/DVI signals) and the best way to hook everything up. 

Here are the different signal types - from worst to best:


Composite Video (Analog, limited to 480i, High Definition not possible)

The lowest quality of video signal, but also one of the most common, found in everything from video games to VHS machines and DVD players. Composite is limited to 480i (standard definition) resolution. Once you’ve seen a higher end high definition signal (720p, 1080i, 1080p), chances are you’ll abandon all sources using composite video, but if you have a large collection of Beta tapes or an old video game, you’ll still need to send a composite video signal to your projector.

Most commercial grade projectors will have a BNC connector for the video connection on the input jack panel. This is a higher grade connector than the consumer RCA jack on the back of a DVD player, and Radio Shack sells a BNC to RCA adapter that will convert the connections. One trick is to use RG-6 cablevision cable as your video cable connection to the projector. That way you can run the video cable up to about 300 feet without loss of the video signal. Simply buy an RCA to F (cablevision connector) adapter at the video source end, and get a second adapter at the projector which is a BNC to F adapter. Then run your cablevision wire between the two.
 

S-Video (Analog, limited to 480i, High Definition not possible)


One step above a composite video signal but still limited to 480i (standard definition) signals. High definition (720p, 1080i, 1080p) is not possible. Relatively speaking, I’d say that an S-Video signal is about 25% better in picture detail than a composite video signal, so wherever possible, use an S-Video feed to send to the projector over a composite video signal.

Use the S-video connection will get about 20% more detail (my estimation) over a composite video connection.

Due to the black and white and chroma (color) signal being run separately within an S-video cable, the general recommended length of an S-video cable is limited to 30 feet or less. Longer runs will show that the black and white and color images will not overlap completely on the screen, and the color portion of the signal can lag the black and white one by " on the screen. I’ve seen this happen in one of my own installations, and the only cure is to use a shorter S-video cable (or buy a very expensive S-video signal booster with adjustable phasing controls on it). It is very easy to bend one of the 4 pins on the S-video cable,  take care not to bend a pin, or a loss of picture or color will result.
 

Component/YPbPr (Analog, 480i to 1080p resolutions supported)

Component (YPbPr) signals come in varying resolutions and can support from a basic 480i standard definition video signal all the way up to 1080p high definition. High definition signals usually come in 1080i or 720p outputs from a high definition cable/satellite box and 1080i, 720p, or 1080p from HD-DVD/Blu-Ray players.

Note: A component signal is NOT the same as an RGB signal even through the color coding is the same. The signals in component cables are broken up differently than those carried in an RGBHV cable so you cannot switch between the two using simple cables.

The introduction of the component signal format has caused more confusion and frustration than any other signal format. Sometime in 1994 (I’m guessing), some brilliant engineer decided that the decades old RGB industry standard for commercial and industrial video was not good enough for the consumer industry, and thus the component format was invented. Even though the three wires that are coloured red, green and blue for the component signal would indicate a plug and play connection to a display or projecto's RGB input, as component signal and RGB signal are NOT compatible. If you connect a component signal to an RGB input, you’ll only get a green image. The R and B output will be very low.

In order to make a component signal compatible with an RGB input found on some displays and most CRT projectors, you need to use a TRANSCODER to convert the component signal to RGB. Naturally, not all transcoders are created equally, so in general, the more you spend on a transcoder, the better quality the RGB output will be. However, some CRT projectors like the Sony D50, G70, G90, Barco 701s and 708, and NEC XG 852 and 1352 do have component inputs along with RGB connections.

We carry various types of transcoders, including models from Audio Authority (see here). We also feature the RTC2200 Component to RGB, TC1500 RGB to Component, and Box1020 RGB to Component converters sold by one of our  third party vendors.


RGBHV (Analog, 480i to 1080p and beyond resolutions supported)

RGBHV signals also come in varying resolutions and can support from a basic 480i video signal all the way up to 1080p and beyond. High definition signals usually come in 1080i or 720p outputs from a high definition cable/satellite box and 1080i, 720p, or 1080p from HD-DVD/Blu-Ray players.

The connectors are typically 5 wire BNC as seen on the above left picture or a D-sub 15-pin (VGA style) connector as seen on the above right picture.

Most CRT projectors will use 5 cable runs to pass the RGBHV signal from the source to the projector: One cable is used for each primary color (red/green/blue), and one for each of the horizontal and vertical sync signals. This is referred to as 'RGBHV'. BNCs are used in higher end equipment as the wires can be made thicker (more robust, longer runs possible). Most consumer display types use the VGA style D-sub 15 pin connector as it takes less space. It's harder to cram large wires into such a short area so most often the cables used won't be as high quality as separate BNC cables.

Some projectors such as certain Ampros and Barco 70x units use four cables: One for each color and one for both the H and V sync signals.  This is referred to as 'RGBs' or RGB with composite sync.

An older format will sometimes only use 3 cables by running the sync signals along with the green video signal. This is referred to as RGsB or RGB with sync on green.


DVI and HDMI (Digital, 480i to 1080p and beyond resolutions supported)

DVI and HDMI are the highest quality signals available. The video signals of a DVI and an HDMI cable are very similar. The HDMI cable is a later version that also adds digital audio (a DVI connector only carries digital video). Adapters to convert the video signal between DVI and HDMI connectors can be found at any good audio video store or online for very cheap.


There are three different DVI connectors:

  • DVI-A: Analog only. Content is found on the four pin group that's separate from the main pin group.
  • DVI-D: Digital only. The four pin group is usually not even present. If it is present, there is no content being carried on it.
  • DVI-I: Both analog and digital. Both groups are active.

DVI you can think of as basically digital RGB, it sends digital 8-bit RGB format signals and supports high resolutions.

HDMI is the newer, more capable version of DVI which adds audio capabilities, where DVI was just designed as a video interface. HDMI also makes high definition copy protection (HDCP) mandatory whereas in DVI it was optional (see below for more on HDCP).  HDMI is backwards compatible, so you can use HDMI-to-DVI adapters or cables and the devices will just revert to basic DVI capabilities which is 8-bit RGB without audio.

If you use HDMI to HDMI, then you're not limited to standard DVI capabilities, and also have digital audio capabilities such as: Dolby Digital, DTS, high-resolution PCM, etc. For Video, HDMI builds on the basically 8-bit RGB capabilities of DVI, it also specs for 8, 10, and 12-bit digital component video (YCbCr) transmission.

The newest version of HDMI (HDMI 1.3 and higher) allows un-decoded high res and high res lossless versions of Dolby Digital (True HD) and DTS (DTS-HD Master Audio) for HD-DVD and Blu-ray disc. HDMI 1.3 and higher also adds support for 'deep colour' which greatly extends the number of colours that can be transmitted in the signal. Support for 'deep colour' in source content today is however non-existent as the Blu-ray and HD-DVD specifications (and DVD and broadcast TV specifications) do not include 'deep colour' and never will as the specifications are done and final. Adding deep colour support today to say, Blu-ray, would make the new discs incompatible with current Blu-ray players. You will therefore not see support for deep colour any time soon in movies. About the only place you may see it is in PC desktops and video games.

Many displays (including all CRT projectors) do not come with any digital input connectors on them, but they're easy to add! Specialized HDMI input cards by Moome for Marquee, Sony, and NEC XG projectors are also available. HDMI can therefore be added to any display with either RGB (VGA) or component inputs without having to replace your TV.

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