You know, because of the differential nature of ILDA signals, it is appropriate to use unshielded twisted pair cables instead of D-25 cables. You can use ordinary CAT-5 flexible network cables, and buy D-25 to RJ-45 adapters at each end for $1.50 (e.g.
http://www.pccables.com/01915.htm,
http://www.pccables.com/01916.htm). You can also use the common type of RJ-45 joiners along the cable without any problem.
The advantage of this technique is that CAT-5 network cable is lighter and more flexible than D-25 cable, it's also cheaper and easier to buy in long lengths. In typical circumstances, signal degradation should be unnoticable over a 500ft cable. With good quality line drivers and receivers, much longer lengths are possible.
One important point of this technique is that you must use ILDA-compliant DACs (which produce differential signals), and amplifiers which sample the differential signals. Also, remember that the +/- components of each signal must use the same twisted pair. Some cheaper DACs only produce single-ended signals, and some cheaper amplifiers only sample single-ended signals. If you use either of these, you must put the DAC quite close to the projector because there is no way to use long ILDA cables without signal degradation. You will even notice it using high quality and shielded D-25 cables.
CAT-5 network cable is ideal for single colour projectors, because there are four pairs which can be used for X, Y, blanking/intensity, and ILDA interlock. If you have an RGB projector, you need to use another type of cable which has more pairs, or use two CAT-5 network cables in parallel.
Best regards,
weartronics