Simplifying testing of multimode fiber optic cables used in LANs and security systems, the FOtest'R duplex cable tester uses a technique of measurement that allows simultaneous bidirectional loss measurements of two fibers and includes a full-duplex talkset for voice communications between test crews. Testing both fibers at once cuts test time in half. The FOtalk talkset built into the instrument lets personnel communicate to compare test results and make certain the data is valid. The combination of these features permit testing two fibers at 850 and 1300 nm in both directions in less than 1 minute.