Tests performed indicate that the SOP will protect the circuit. Because the SOP limits the current to 200 mA, it prevents both the –35 V and the –70 V power supply voltages from being forced negatively. Figure 2.10-6 shows the new circuit configuration. A field trial, where one of the two circuits was protected by a GDT and the SOP, has proved the success of the proposed protection. Within a few weeks of the installation, a lightning storm damaged the circuit protected by a GDT whereas the one protected by the combination of a GDT and the SOP continued to operate. Protected termination module GDTs Pair 1 to building Pair 2 to building Antenna and electronics SOPs Power supply 0V V d.c. Earth Earth bolt Earth reference via power supply Mounted at top of pole Mounted on pole 1-3 m above ground Miti(08)_F2.10-6 Figure 2.10-6 – GDT and SOP protected system References Rec. ITU-T K.30 Case study 2.10 – 6 –