Industrial AN GTM-12 Telephone Cable Test Set

Industrial AN GTM-12 Telephone Cable Test Set is a USGI military field diagnostic tool designed to test CX-4566/G 26-pair telephone cables. The unit connects to CX-4566/G cables via the W100 adapter to J100, with the cable under test attached to the U-185B/G connector on the adapter, and it can operate from AC power or an external DC source. During testing, it sequentially interrogates each wire pair for continuity (CONT P), insulation resistance (IR), and cross-talk (X TALK), displaying the pair numbers as it sweeps through the 26 pairs; if a fault is detected, the FAULT indicator illuminates and the defective pair numbers are recorded, and the END indicator signals completion after the test sequence. A CABLE LENGTH selector allows the tester to be set to the measured cable length (or a combined length when testing multiple connected cables), and AUTO/SINGLE selects continuous automatic cycling or manual stepping through tests, while FUNCTION selects the test mode (CONT P, IR, or X TALK). Safety precautions require disconnecting the tested cable from any load or power source before beginning, and to follow the associated procedures for wiring to J100, U-185B/G, and the W100 adapter. The AN/GTM-12 is documented in Army troubleshooting guides as a dedicated 26-pair cable tester used with CX-4566/G family cables in field and workshop environments, enabling technicians to verify conductor continuity, detect insulation faults, and identify cross-talk across all pairs, making it a purpose-built tool for military telecommunications maintenance.