The CU-1-1500 is used as a 1:1 unun(aka feed line choke, line isolator) for 50 ohm unbalanced coax cable input to 50 ohm unbalanced coax output at full amateur radio legal power (1500-watts PEP) into a matched load 50 ohm load. The unun is designed to have a high RF impedance to common mode currents on the outside of the coax braid while passing RF currents on the inside of the coax braid to the antenna.
The CU-1-1500CB has been optimized for the 11-61 MHz range. Works well with amateur radio tri-band beam antennas and very good for 11 meter operation as well.
For most effective results, use 1 choke at the antenna and another at the radio end of the coax. Helps reduce noise floor too by choking off common mode neighborhood noise picked up on outside of coax braid.