The Hy Power BLLI-250 is a 50 ohm inline isolator with two SO239 connectors for coupling your coax. The line isolator is used to isolate any RF (common mode) that may have worked its way back to your station. It uses the Guanella current/choke design. The power handling capability of the line isolator is conservatively rated at 250 watts from 160 to 6 meters. It will safely handle peak power ratings of up to 350 watts. These ratings are good up to a 2:1 SWR.
The MIL SPEC transmission line used to make the isolator uses: silver clad copper center conductor, silver covered shield, solid Teflon dielectric with a temperature range from -100° to +200° centigrade.
If you are using a transmatch, connect the line isolator to the input (station side) of your transmatch. Do not place it on the antenna side of the transmatch. Most matching networks that have a balun installed use a 4:1 voltage balun. These baluns are usually not adequate for choking RF from working its way back to your rig.