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Where Do I Go from Here? Recently, I submitted a bid for the purchase of numerous video projectors (new and replacements) that would be installed across
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FEEDBACK

Dec 1, 2002 12:00 PM

Where Do I Go from Here?

Recently, I submitted a bid for the purchase of numerous video projectors (new and replacements) that would be installed across our campus. I have been a happy user of Sharp projectors for the past four years. They are quite reliable, and I have had excellent service and support when things fell a little short of total perfection in the past.

However, one thing that has concerned me as we move away from CRT production technology and more into LCD, DLP, and beyond is our simultaneous expanded need for greater synchronization and resolution capabilities because of our expanded use of computer-aided teaching in the classroom. College faculty and staff are making impressive strides in requesting more contemporary classroom computer media applications. They're also requesting multimedia system access from their laptops in classrooms across our campus — so much so that we now include VGA ports on instructor consoles in new multimedia classrooms and are also retrofitting our old multimedia classrooms with this seemingly simple fix.

I have a simple understanding of the importance of certain specifications relating to video line resolution and the Dot Clock for image quality (especially without a scaler) and vertical and horizontal frequencies relating to synchronization with computers. These specifications are important, especially for the highest multimedia classroom system computability with new resident computers, their hardware, and visiting laptops. Unfortunately, I am having a difficult time finding good documentation to better educate myself and others in these areas.

Can you please point me to literature that explains those items and their relationship to video projectors and computers?
Bob Racette
via e-mail

A good place to start is the Extron Electronics Web site (www.extron.com), which contains a wealth of information on interfacing video and computer signals. Go to the Web site and start your search for FAQs and other information resources.

Don't forget to check for bandwidth specifications, as well. Just because a given projector can support a wide range of horizontal sync and vertical refresh rates doesn't mean it has enough bandwidth to pass all of the signal.

A simple formula for calculating bandwidth is BW = [(TP * Vt)/2]3, in which TP is the total number of displayable pixels and Vt is the vertical refresh rate in Hertz.

If you want to determine the required bandwidth for a 1,280-by-1,024 signal with a 72 Hz refresh rate, the calculations would be:

  1. 1,280 × 1,024 = 1,310,720 pixels
  2. 1,310,720 × 72 = 94,371,840
  3. 94,371,840/2 = 47,185,920
  4. 47,185,920 × 3 = 141.5 MHz

Restricted bandwidth is a problem with 720p and 1,080i HDTV signals as well as SXGA (1,280 by 1,024) and UXGA (1,600 by 1,200) sources. Many projectors on the market claim to support those formats, but my actual test results have been mixed, both in terms of sync compatibility and bandwidth.
— Pete Putman

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