The OP930-D is a dual channel insertion and return loss tester. The OP930-D is similar to the OP930 except an additional source port and detector is added to streamline testing of duplex cables and to allow for simplified testing of cables with unlike connectors. The test system has two source ports and two power meters. While Port A and Port B are treated as two separate channels, they share the same source modules and are regulated by a 1×2 switch, activating on one channel at a time. The corresponding power meters are configured to expect readings from their respective source ports when that source is switched on.