I know this is probably not the best group, but there are so many clever people here!!
At Church we have a projector run over a 20m long, reasonable quality VGA cable strung across the roof trusses. AT ground level we have an induction loop driven at audio frequencies for hearing aids.
The latter appears to cause ripples in the display from the former.
Any thoughts on minimising the effect?
20m is quite long for a VGA cable.
You can get drivers that work over larger distances using balanced cables which resist interference better.
However you really want to be in the digital world.
Can you use DVI/HDMI rather than VGA?
Shorten the projector cable and lengthen the audio one or go digital.
Try sci.electronic.design if you want chapter and verse.
Why do you say lengthen the audio cable? It feeds an inductive loop amp, and the loop is inducing the "sound on vision" problem.
^^^^^ If going the balanced driver route - 100 squid for a pair of vga to lan adapters with psu. Claims it's good for 80m @ 1920*1200 max over (decent) cat5e
OP, does the interference cease with a test laptop (on battery) and a short vga cable? Just wondering if the loop is causing mains borne interference to the projector.
move the computer to the screen and use a longer mosuse and keyboard line, or ethernet and a remote access program.
The Blue Room forum is quite knowledgeable about audio-visual stuff.
Here's an example:
Claimed performance is Maximum VGA resolution & distance: 2048 x 1536 @ 180m
Full spec details:
Could be a loop generated between the VGA cable and the mains supply to the projector. This is easy to test - run a temporary mains supply to the projector back alongside the VGA cable (spaced a few inches apart), and plugged in the same outlet as the laptop, and see if this stops it.
Don't worry it appears that some don't know what an AFILS is. I doubt it is getting into the long VGA cable but into the display section or maybe the PSU of the projector itself.
Might be worth temporally connecting the PC to the projector with a short cable and seeing if the ripples disappear. Keeping the projector in the same place though!
20m would be fun for DVI/HDMI so "going digital" may not help and if the PC doesn't have DVI/HDMI out pretty much a non-starter, one may as well try the VGA baluns.By the nature of the AFILS curing this could be a right begger.
What make projector? Have you checked it is the VGA cable by trying it with a shorter one?
Have you tried prayer?
It didn't work.
You're still here :-)
MBQ
You are almost certainly seeing the effect of current flowing in a large ground loop coupling to the varying vertical magnetic field in the room. This loop most likely consisting of the long VGA cable and connections from the projector and signal source to the ring main earth.
ISTR The audio input to AFILS is balanced twisted pair and tolerates long cable runs in the vicinity of its own magnetic field much better.
Basically make the video signal path as short as you can and if that means running a longer audio path so be it.
Don't make unwarranted assumptions. I installed one in our village hall and it does not affect the (digitally connected) projector in any way. Using long signal path cables in a zone where there is a fluctuating magnetic field can be hairy as the OP has found out.
On this we are agreed. If it is pick up inside the projector then placing a thin sheet of soft iron underneath it wrapped in aluminium foil might help ameliorate the effect to some extent. mu-metal sheet if you want to be posh but I think that it is so unlikely to help that it isn't worth spending any money on this approach.
Moving the video signal source closer to the projector will probably help a lot as will powering both units from a common source- otherwise you have lots of large ground loops about with circulating currents.
Martin Brown wrote in news:Igxbs.3580$ snipped-for-privacy@newsfe10.iad:
I have seen similar signs in a large conference room. I thought it was due to vibration from the speakers in the ceiling. (Could it be??)
=E5=9C=A8 2012=E5=B9=B410=E6=9C=885=E6=97=A5=E6=98=9F=E6=9C=9F=E4=BA=94UTC+=
8=E4=B8=8A=E5=8D=883=E6=97=B649=E5=88=8603=E7=A7=92=EF=BC=8CJohn=E5=86=99= =E9=81=93=EF=BC=9A
Of course it didn't work. Chanting to sky fairies is a waste of time.
And next you'll be getting all aggressive with me and blaming me for it.
Thanks for the suggestions, since the projector is 4m up in the air it may take a while to try them all!
In message , John writes
Surely, prayer should work
If a god made the laws of nature, shirly he could bend them just a bit for his followers
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