The W5GI multiband collinear antenna combines wire radiators and coaxial phasing sections to deliver reliable HF coverage from 80–6 m. A tuner-friendly alternative to the G5RV with strong multiband performance and efficient radiation for practical ham radio installations Despite being far shorter than a full-size quarter-wave 80-meter radiator (approximately 20 meters), this design uses a smart combination of loading coil, coax-based impedance matching, and careful geometry to achieve a practical match at 3.650 MHz.
This antenna design has been optimized for operation at 3.650 MHz and features a carefully engineered matching network to ensure efficient power transfer to your feedline.
Antenna Physical Specifications
This ground-mounted shortened vertical antenna with the following key dimensions:
- Total height: 4 meters (approximately 13 feet)
- Radiating element: 1.8 meters from ground to loading coil
- Loading coil position: 1.8 meters above ground
- Tube diameter: 20mm (approximately 0.8 inches)
- Loading coil inductance: 64.15 microhenries
The antenna uses a continuous tube construction with a loading coil positioned at the 1.8-meter point. This placement provides an optimal balance between radiation efficiency and mechanical stability.
Loading Coil
The loading coil is critical to the shortened vertical antenna performance. At 64.15 microhenries, it compensates for the shortened physical length, allowing the antenna to resonate on the 80-meter band despite being only a fraction of a quarter-wavelength tall.
Key specifications:
- Inductance: 64.15 μH
- Position: 1.8 meters above ground
- Function: Provides inductive reactance to electrically lengthen the antenna
Matching Network for 3.650 MHz
Since the feed-point impedance of this shortened vertical won’t naturally match standard 50Ω or 75Ω coaxial cable, a matching network is required at the base. The design includes an LC matching circuit consisting of a series inductor and shunt capacitor.
Ground System
As with any vertical antenna, a good ground system is essential for optimal performance. Consider installing at least 16-32 radials, each approximately 20 meters long (quarter-wavelength at 3.650 MHz). More radials will improve efficiency.
Weatherproofing
The matching network components should be housed in a weatherproof enclosure at the antenna base. Use high-quality capacitors rated for RF service and ensure all connections are properly sealed against moisture.
Tuning
The specified component values are optimized for 3.650 MHz. If you need to operate at different frequencies within the 80-meter band, you may need to adjust either the loading coil position or the matching network values. An antenna analyzer is invaluable for fine-tuning.
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