HB9XBG Antenna
Vertical dipole using speaker cable as feedline and lower radiator.
The HB9XBG antenna is a vertical dipole antenna for short wave radio amateurs, developed by the Swiss radio amateur Walter Kägi, whose call sign HB9XBG also designates the antenna. It is notable for its use of a speaker audio cable as both feedline and lower radiating element, eliminating the need for radials or a ground grid, and for its ability to operate with the feedpoint at the base while functioning electrically as a centre-fed dipole.
- Developer
- Walter Kägi (call sign HB9XBG)
- Frequency bands tested
- 20-metre and 40-metre amateur radio bands
- Test location
- Simplon Pass at an altitude of 2,040 metres
- Feedpoint impedance
- 100 Ω
- Bandwidth
- 900 kHz with SWR less than 1.5
- Antenna gain
- 6 dBi over ideal terrain
- Radiation resistance at dipole centre
- 100 Ω when lower leg end is λ/80 above ground
Lore & Background
The HB9XBG antenna was developed by Swiss radio amateur Walter Kägi, whose call sign HB9XBG became the antenna's name. During the test phase in 2020, two vertical dipoles were built—one for the 20-metre band and another for the 40-metre band—and tested on Simplon Pass at an altitude of 2,040 metres. The structure was first published in 2020 in HBradio, the journal of the Union of Swiss Short Wave Amateurs.
The antenna is based on a speaker audio cable with a strand cross-section of 2 × 2.5 mm² and PVC insulation, which has an impedance of almost exactly 100 Ω. This cable performs two functions: it serves as the feedline to the dipole centre and as the radiating common mode current for the lower dipole leg. One core of the two-core cable is removed on the upper half of the dipole. A resonant trap L2/C2 eliminates common mode current at the lower end, and components L1/C1 match the 50 Ω feedline impedance to the 100 Ω system.
Despite the feedpoint being applied at the base, electrically the antenna is a centre-fed dipole. The radiation resistance at dipole centre depends on installation height; when the lower leg end is λ/80 above ground, the radiation resistance is 100 Ω, with ground conductivity and dielectric characteristics exerting little influence.
Reader's Guide
The HB9XBG antenna represents a practical solution for portable and fixed short wave operation where space and ground conditions are challenging. Its design eliminates the need for radials or counterpoises, making it suitable for rocky terrain and Summits on the Air activations. The use of common speaker cable as both feedline and radiator simplifies construction and reduces cost, while the low-impedance feed of 100 Ω and flat SWR curve over 900 kHz allow operation without an antenna tuner. The antenna achieves a low take-off angle of radiation, described as ideal for DX, and a gain of 6 dBi over ideal terrain. Its rapid setup and dismantling, combined with installation only a few centimetres above ground, make it particularly attractive for portable use. The design was published in the Swiss amateur radio journal HBradio in 2020, and its development and testing at high altitude on Simplon Pass demonstrated its performance in real-world conditions.
Did You Know?
- The HB9XBG antenna uses a speaker audio cable with 2 × 2.5 mm² strand cross-section and PVC insulation as both feedline and lower radiating element.
- The radiation resistance at dipole centre is 100 Ω when the lower leg end is λ/80 above ground.
- The antenna achieves a bandwidth of 900 kHz with SWR less than 1.5.
Frequently Asked Questions
What is the HB9XBG antenna?
It is a vertical dipole antenna designed for shortwave radio-amateur use, created by Swiss operator Walter Kägi, whose call sign HB9XBG gives the design its name.
What makes the HB9XBG antenna stand out from other verticals?
Its defining trick is repurposing a standard speaker audio cable to serve simultaneously as the feedline and the lower radiating element, so the operator never has to install radials or a ground grid.
What are the measured performance specs of the HB9XBG antenna?
The feedpoint presents a 100-ohm impedance, the usable bandwidth stretches to 900 kHz while keeping SWR below 1.5, and the gain reaches 6 dBi when placed over ideal terrain.
Where and on which bands was the HB9XBG antenna field-tested?
Walter Kägi validated the design on the 20-metre and 40-metre amateur bands at the Simplon Pass, sitting at roughly 2,040 metres above sea level.
Why do radio-amateur fans consider the HB9XBG antenna important?
It lets a ham achieve the electrical behaviour of a centre-fed dipole with the feedpoint at ground level, all without the usual radial or ground-grid infrastructure, making it a remarkably simple portable option.
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