How much bandwidth is required in a VGA switcher?? - AVS Forum
Forum Jump: 
 
Thread Tools
post #1 of 5 Old 06-03-2001, 07:35 PM - Thread Starter
dj
Member
 
dj's Avatar
 
Join Date: Nov 2000
Location: Perth, Australia
Posts: 37
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
I need to buy a switcher to take multiple VGA sources into my Davis projector (single DB15HD input). I have a well priced 6 in 1 out Kramer switch available which has a bandwidth of 180MHZ and was wondering if this is enough? My sources will be PC (Geforce2) at XGA, a Dreamcast console (using VGA breakout box), a HDTV set top box, a satellite tv set top box, and possible a laptop from time to time.
Can anyone comment, Im striving for that champagne on a beer budget again http://www.avsforum.com/ubb/smile.gif
dj is offline  
Sponsored Links
Advertisement
 
post #2 of 5 Old 06-03-2001, 07:53 PM
AVS Special Member
 
JoeFloyd's Avatar
 
Join Date: Apr 2000
Location: Fairfax, VA, USA
Posts: 1,384
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
350 Mhz is the number that is often used. 350 Mhz gives you plenty of head room for higher scan rates and higher resolutions.

For example, a line doubled 1080i signal would require

1920 X 1080 X 60 = 124 Mhz dot clock

To correctly pass this signal, you should roughly double the dot clock frequency for the bandwidth of the switching equipment. That means about 250 Mhz.

Many computer displays can achieve a combination of resolutions and refresh rates that will easily exceed a dot clock of 124Mhz, so having a little extra bandwidth gives you some room to grow.
JoeFloyd is offline  
post #3 of 5 Old 06-03-2001, 09:18 PM
Senior Member
 
Mark II's Avatar
 
Join Date: Dec 2000
Location: DFW, Texas
Posts: 317
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
JoeFloyd,

Is there a bandwidth limit on cables as well. I added a VGA extension cable to an existing 25 ft VGA cable and the input from my laptop would no longer sync with the projector. I'm hoping adding a quality powered switcher such as http://www.altinex.com/Solutions/switchers/da1916sx.htm will eliminate the problem. But am not sure on the type VGA extension cable I should use.

Thanks for the info.

------------------
Mark II

Mark II

I am a nobody, and nobody is perfect; am I therefore perfect?
Mark II is offline  
post #4 of 5 Old 06-03-2001, 09:45 PM
AVS Club Gold
 
Mark Petersen's Avatar
 
Join Date: Dec 2000
Posts: 4,671
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 11
Does anyone know how well these switchers work with a DILA? I currently run 3 video cables to my DILA (VGA, RGBHV and S-VHS). Since my cable run is going to be around 40 feet, I'm going to replace my current cable with high quality cables like bettercable. But I'm thinking that it may be better to put the money for 3 cables into one cable plus a switcher.

Currently, my HDTV STB uses the RGBHV input and always synchs to the HDTV input source, while my computer uses the VGA and synchs to the computer3 input source.

If I use one cable, plus a switch would I feed everything into the RGBHV input to the projector? Would this be an optimum setup or would I be losing something in the process?

Anybody have any ideas?

Thanks,
Mark

------------------
Calibrated G11 DILA, 7' 16x9 Greyhawk, Radeon HTPC, Panamorph (soon), DTC-100, AccessDTV, Lexicon MC-1+, B&W Nautilus 804's, HTM1, SCM1s
Mark Petersen is offline  
post #5 of 5 Old 06-03-2001, 10:31 PM
AVS Special Member
 
JoeFloyd's Avatar
 
Join Date: Apr 2000
Location: Fairfax, VA, USA
Posts: 1,384
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
The main difference between different switchers are buffered vs. unbuffered.

Buffered switchers are preferred since they provide electronic isolation along the signal pathway. This will result in a more stable picture with less ghosting, or other forms of signal degradation. These are also the most expensive type of switcher.

Full mechanical switchers are by definition unbuffered, but that doesn't mean that they cannot provide very good image quality. The design of the mechanical switch components has to be carefully performed to avoid all the common forms of signal degradation. While there is a science to these things, there is still a lot of art to perfecting all the details.

Cables and connectors have a lot a variability. The cables and connectors are designed with a given signal bandwidth in mind, but since they are analog devices there is a lot of variability from one cable to the next as well as from manufacture to manufacture. The best choice when it comes to cables is to find a review from someone with a similar application and see what they had to say. BetterCables is often given high praise for the quality of their products, but DigitalConnection also sells VGA cables that should be of high quality.

With longer cable runs it difficult to produce cables that will not be a source of some image degradation and buffered switchers or distribution amplifiers can be very helpful for these situations. Again, the best advice is to search for a product review that seems to be similar to your application.
JoeFloyd is offline  
Closed Thread Digital Hi-End Projectors - $3,000+ USD MSRP

User Tag List

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page


Forum Jump: 

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off