Gordon Elliott <[EMAIL PROTECTED]> wrote: > > Hi, Arthur, Hi Gordon,
Please excuse me for delayed answer. > I don't think we disagree on much except for a particular > detail, so I'll only respond to that. Ok. > The circuitry to do the subtraction is expensive, especially at video > frequencies. But I don't deny that the monitor might have such a > circuit--since neither of us have the schematics we can't determine that for > certain for a given monitor. Giving the absence of schematic diagram for this particular display, I don't know exact details either, but many expensive monitors are designed with true separate grounding of signal lines. Please note that I'm using the word "differential" in double quotes; just to put the whole idea simpler. BTW, Apple prefers to use real differential technology in another place - the Mac's serial ports are an example of that, so I suppose the monitor circuitry is also made with good design... > However, whether the monitor uses a differential receiver is not > particularly relevant to our problem here. The reason is that any "adapter" > would be applied at the transmitting end (the computer), not at the > receiving end. As long as the transmitter side (such as our "adapter") does > not add noise to the signal return grounds, even if the receiver has a > differential circuit it will work without newly created noise. Hmm, I'm still thinking that the ground lines should be kept separate on both ends of cable. Properly designed transmitter must use the signal return ground to ensure normal operation of particular line, and connecting the grounds together will block 'current loop' there. > if you do separate the grounds in a WIRED adapter or > cable, that is also entirely appropriate. The currents do indeed flow > "differentially" whether or not the receiver uses differential circuits, and > improperly wired can introduce noise. -snip- > You're on the right track, and method will work--I only disagree on some of > the details of your comments. Improper grounding can most certainly > introduce unwanted signal distortion. It's my understanding as well. Anyhow, after several days of searching and soldering, I've made my own cable. In case it's useful for others, I've found good page: http://www.saragossa.net/intfcing.html Unfortunately, the suggested schematic is not perfect - the ground lines on the VGA side are tied together, but main advantage of that article is, a good information about Mac's monitor detection technique. I wasn't aware that there's diode involved! :-) My variant is very close to the one shown on that page, with two exceptions: I've inverted the diode, and connected all the ground lines separately. In addition, the cable I've used, does have cylindrical ferrite inductive filters on the both ends. Now I can proudly report, that I have excellent picture quality - crisp & clear! > (PS I have designed a lot of equipment that has to meet better than 100 dB > analog signal/noise standards, which are levels that can only be dreamed > about by video designers. And also equipment with both differential and > single ended signals approaching gigahertz frequencies.) You know, my job was a electromagnetic liquid flowmeter's development - very weak signals in presence of high-level noises (both electrical & magnetic), with strong requirements for the accuracy and stability... Best wishes, Artur -- Quadlist is sponsored by <http://lowendmac.com/> and... Small Dog Electronics http://www.smalldog.com | Enter To Win A | -- Canon PowerShot Digital Cameras start at $299 | Free iBook! | Support Low End Mac <http://lowendmac.com/lists/support.html> Quadlist info: <http://lowendmac.com/lists/quadlist.shtml> --> AOL users, remove "mailto:"; Send list messages to: <mailto:[EMAIL PROTECTED]> To unsubscribe, email: <mailto:[EMAIL PROTECTED]> For digest mode, email: <mailto:[EMAIL PROTECTED]> Subscription questions: <mailto:[EMAIL PROTECTED]> Archive: <http://www.mail-archive.com/quadlist%40mail.maclaunch.com/> Using a Mac? Free email & more at Applelinks! http://www.applelinks.com
