The HB9XBG antenna is a vertical dipole antenna for short wave radio amateurs. It was developed by the Swiss radio amateur Walter Kägi, whose call sign HB9XBG is also the designation of the antenna.[1] During the test phase in 2020, HB9XBG built two vertical dipoles – one for the 20-metre amateur radio band and another for the 40-metre band. The antennas were tested on Simplon Pass at an altitude of 2,040 metres. The structure of the HB9XBG antenna was first published in 2020 in HBradio, the journal of the Union of Swiss Short Wave Amateurs.[2][3]