Yaesu FC-20 Antenna Tuning Unit, The Yaesu FC-20 HF/50MHz External Automatic Antenna Tuner is ideal for tuning out minor SWR variations in your antenna system in conjunction with the FT-847. The FC-20 analyses the impedance present at the radio end of the coax, and adjusts the impedance to match the 50 Ohm requirement to the FT-847or FT-100. It utilises fixed inductors and variable capacitors controlled by stepper motors. The FC-20 can accommodate SWRs of up to 3:1 on HF and up to 2:1 on 50MHz. It also provides up to 100 memories that contain band and tuning data of your favourite frequencies. It includes an Auto-Start feature in case the antenna impedance suddenly changes.