elliot@xenna.encore.com (Elliot Mednick) (11/20/90)
Is there a rule-of-thumb on how long a (S)VGA cable can be? I attempted extend a 2-foot cable with a shielded db9-to-db9 6'cable. This causes (not-too-unexpectedly) shadows, ghosts, and funny lines. (BTW, ignore my earlier query on VGA memory tests -- the problem was the cable length!) What is the difference between a VGA cable and a shielded serial cable (besides the 15-pin connector)? __ Elliot Mednick (elliot@encore.com) | This .signature file is undergoing Encore Computer Corp. | remodeling for your convenience. Marlborough, MA. 01752 | Please pardon our appearance.
grege@gold.gvg.tek.com (Greg Ebert) (11/21/90)
In article <13304@encore.Encore.COM> elliot@xenna.encore.com writes: >Is there a rule-of-thumb on how long a (S)VGA cable can be? I attempted >extend a 2-foot cable with a shielded db9-to-db9 6'cable. This causes >(not-too-unexpectedly) shadows, ghosts, and funny lines. (BTW, ignore my >earlier query on VGA memory tests -- the problem was the cable length!) > >What is the difference between a VGA cable and a shielded serial cable >(besides the 15-pin connector)? > The shielded cable is terminated with it's characteristic impedance, hence there will be minimal (ideally none) signal reflections (ie 'ghosts'). The printer cable has a shield around all conductors collectively, whereas the video cable has individual shielded wires. Guess what ? You have an impedance mismatch with the printer cable. Another problem with the printer cable is that there will be coupling between the R,G, and B signals; don't worry about HSYNC and VSYNC because video is probably blanked when these guys wiggle.