The RU-4:1 Unun was designed to allow easy interface of LDG S9 vertical antennas to the LDG line of Automatic Antenna Tuners. The 200 watt Unun also operates "stand alone", thus does not require an LDG Tuner for resonant verticals. It may also be used with many of your antenna projects where a 4:1 Unun is needed.