Measure the required length of the cable, then cut a piece from the reel, leaving an extra 4 inches to allow for the connections. Strip 1 inch of insulation from one end of the cable.
Unscrew the conical strain relief cap from the base of each connector. Thread one of the conical pieces onto the cable, with the wide end toward the stripped end of the cable.
Connect the soldering iron to the mains and allow it to heat up. Separate the wires within the cable. There are five wires within the cable, but most DMX equipment only uses the first three pins, Avolites desks use the additional two wires as an extra data channel, essentially making two cables that share a ground wire.
Solder a twisted length of the inner cable screen to the first pin. This will act as the ground and help cut interference. Two wires within the cable will act as the positive and negative data channels. Select two of the wires, noting the colors, and solder them to pins two and three. Repeat this process at the opposite end of the cable, ensuring you solder the same pair of wires to pins two and three.
Screw the conical strain-relief section onto the connector at each end of the cable. Slip a 5-inch length of heat-shrink over the point where the cable disappears inside the connector. Heat it with the heat gun until it has contracted tightly around the connector and the cable.