An FMC+ Loopback Test Module (or FMC+ Loopback Card) is a specialized diagnostic hardware tool used by hardware engineers, FPGA developers, and manufacturing test teams to validate the interfaces and signal integrity of FPGA carrier cards equipped with VITA 57.4 (FMC+) expansion slots.
Please find the detailed product information here:
VITA 57.4 FMC+ Loopback Test Module