the signal dose get week over great distances so u would want to put something like an in-line opto, or opto isolator, or even an opto spliter, all of the above will take the DMX signal and amplify it for longer runs. the spliters are really nice if u have to use a patch bay for your dmx or if you want to split up 1 universe of dmx to more than one electric without having to use non-powered spliters or link a bunch of battons together with one run
Opto Spliters is basicly a multipul repeater for DMX which takes an incomming signal and then takes the same information and copy's it to send it down several other cables.
"DMX rules require daisy chain style wiring
with no breaks, stars, tees or un-terminated
ends. When this isn’t practical, a DMXOpto
Repeater can be used to properly distribute DMX to dimmers, scrollers or other devices
in a star configuration. Similarly, a DMX Opto Repeater can be configured to permit a
star input configuration for consoles or other DMX sources."
Opto-splitters also provide a degree of electrical isolation, to protect multiple lines of DMX and the console. Opto-splitters contain opto-isolators (hence the "opto" part.) Opto-isolators are microchips that contain minature infra-red LEDtransmitters, and infra-red recievers. The DMX signal goes through the LED (binary "1" turns the LED on, and binary "0" turns it off.) The reciever repeats the signal and outputs it. However since there is no direct eletrical connection between the transmitter and reciever, if there is a fault in a DMXline (such as a short), it will not carry through to other lines. Additionally, the console is protected from high voltage shorts. (cheaper to replace a few opto chips than a console.) You can also buy single opto-isolators. They look like a small cylinder with XLR IN, OUT and power. They are a cheap way to protect consoles.
Hope this helps
There's a great thread currently on the Stagecraft mailing list on this very topic. The basic consensus is that you really don't need a splitter/repeater unless you're running over a few hundred meters. Although according to Jerry Durand, "RS-485 (the basis of DMX) with one transmitter at one end of the wire and one receiver at the other and good wire in between should be good for approaching a mile."