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Projector Cable Choices

VGA Cables are still the most used cable for projectors in education despite digital HDMI technology becoming more popular

VGA cable 5 Coax with FerriteVGA Cables for installation, have different requirements to the trailing cables and cords used for direct connection or to a wall plate, as they are used where the position of the projector is fixed. A table top projector may be connected to different computers and at different distances from the screen each time it is used. Consequently whether a fixed installation needs DDC ie extra wires in the VGA cable to automatically adjust the picture qualities is debatable (DDC is not really needed for fixed PC installations and may only be useful where laptops or notebooks are used).

Another consideration is where to use ferrite beads to prevent Radio frequency and Electromagnetic intererence. Ferrite beads should be used at about 50mm from either end of a cable run. So in the case of the installation cable a ferrite bead should be fitted to the projector cable at the projector end. (The computer should be connected to the cable kit using a short cable with a ferrite bead at the computer end of the cable)

The next question is whether the Horizontal sync and Vertical sync wires should also be coaxial pairs, the same as the Red Green and Blue (RGB) coaxial pairs ie whether to use 3 coaxial pairs or 5 coaxial pairs. We would recommend using coax for the sync signals to reduce interference.

And lastly the screening of the overall cable should be sufficient to prevent interference, this is often measured in "percentage cover" of the braiding or drain wire and foil. Braiding alone would normally have less than 100% cover as there are gaps in the braid, a design with  a drain wire and foil "covers" the gaps 100%.

These design issues affect the video performance of the system, seen as "ghosting" to a greater or lesser extent in the projected image, not forgetting that picture quality is also affected by the length of the cable, connection mismatches, device output levels and the set-up of equipment.

There are choices for VGA cables with 3 or 5 coaxial pairs, with and without DDC wires and with and without ferrite beads to suit conditions and budget.

A 5 coax VGA cable without DDC or ferrite beads at the projector is the norm for the vast majority of education users.

 

Useful links

AV Cables for projector installs

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