VertiCore 1/4th: The Reliable Workhorse for 15, 17, and 20 m
VertiCore 1/4th: The Reliable Workhorse for 15, 17, and 20 m
A rigid, band-specific quarter-wave radiator over four elevated 45° quarter-wave radials, measured as one monoband feed system for RX and TX.
The 1/4λ VertiCore is intentionally simple: one full-size monoband radiator, four rigid elevated radials, a measured driving point and a tested 1:1 balun. It avoids traps and loading coils, but its 50 Ω region still belongs to the complete radiator/radial geometry—not to the vertical tube alone.
Why Use 1/4λ on 15, 17 and 20 m?
On these bands, a mechanically rigid quarter-wave radiator remains practical. That allows the current maximum to stay near the feed region without the conductor and dielectric stress of a shortening coil or the extra resonances of a trap. The antenna remains monoband: each version has its own radiator and radial dimensions.
| Band | Radiator | Return system | Design priority |
|---|---|---|---|
| 20 m | Band-specific 1/4λ aluminium radiator | Four elevated 45° 1/4λ radials | Full-size monoband vertical within a practical rigid structure |
| 17 m | Band-specific 1/4λ aluminium radiator | Four elevated 45° 1/4λ radials | WARC-band operation without multiband interaction |
| 15 m | Band-specific 1/4λ aluminium radiator | Four elevated 45° 1/4λ radials | Compact full-size monoband geometry |
The Elevated Radials Establish the Return Path
A quarter-wave monopole is only half of the RF current system. The four radials carry the return current and contribute to both impedance and radiation. VertiCore raises them above ground and inclines them at approximately 45°, creating a defined counterpoise instead of asking soil, mast and coax to complete the circuit accidentally.
- Length is band-specific. Each radial is prepared for the selected monoband version.
- Symmetry matters. Unequal angles, heights or nearby conductors change current division.
- Clearance matters. Radial tips close to roofs, soil, fencing or wiring alter capacitance and loss.
- The mast matters. A conductive support inside the radial field can detune the system or carry RF current.
How the Feed Approaches 50 Ω
The sloping-radial geometry and radiator driving point are developed as one assembly. Changing radial angle changes both resistance and reactance; changing height or nearby structures changes them again. RF.Guru measures the production geometry with the complete radiator, radial hub and 1:1 balun present.
The 1:1 balun is for common-mode control. It does not transform an arbitrary quarter-wave feed impedance to 50 Ω. The radiator and radial geometry establish the nominal input, while the balun limits unwanted current on the coax exterior.
A minimum SWR reading alone cannot distinguish radiation resistance from conductor, contact, dielectric or return-path loss. Use complex impedance across the operating band and verify outside-of-coax current after installation.
Mechanical Construction
The product uses a rigid marine-grade aluminium radiator with a nominal 35 mm outside diameter and 2 mm wall in the referenced construction, together with RVS/INOX 316 stainless hardware. Rigid radials keep the return geometry more repeatable than loose wires whose angle changes with wind and attachment point.
Clean aluminium joints, apply a compatible anti-corrosion compound according to its instructions, keep connector mating surfaces clean and dry, and inspect torque, radial symmetry, weather sealing and feedline strain relief periodically.
Height and Clearance
For a quarter-wave radial of length Lr inclined downward at 45°, the vertical drop is approximately 0.707 Lr. A mechanical clearance check can therefore use
Hfeed ≥ 0.707 Lr + C
C is the selected tip clearance above the local surface or accessible area. This calculation prevents the radials from striking or approaching objects; it does not prescribe a universal takeoff angle or RF-optimum height.
Installation and Verification
- Assemble the band-specific radiator, all four radials, hub and selected 1:1 balun.
- Install the radial plane high enough for the required tip clearance.
- Set all four radial angles and surrounding clearances as symmetrically as practical.
- Route the coax away from the radial plane at right angles initially.
- Measure at the feedpoint or de-embed a characterized feedline.
- Record complex impedance across the operating band and outside-of-coax current.
- Repeat after final mast, bonding, feedline and nearby cable placement.
Pattern boundary: a quarter-wave vertical has a familiar broad elevation response, but installed takeoff angle and realised gain still depend on height, ground, radial currents, mast, feedline, nearby structures and loss. Do not turn one model or one site measurement into a universal angle.
Power-Service Options
The current VertiCore product offers measured and tested 6 kW and 9 kW 1:1 balun service options. The usable station limit remains conditional on frequency, waveform, PEP and average power, duty cycle, tune duration, mismatch magnitude and phase, connector/feedline rating, temperature and installation. Select the required margin and operate within applicable licensing and RF-exposure rules.
Mini-FAQ
- Which bands use the VertiCore 1/4λ geometry? The band-specific 15 m, 17 m and 20 m versions use 1/4λ radiators with four elevated 45° quarter-wave radials.
- Do the sloping radials matter to the 50 Ω feed? Yes. Their length, angle, height and symmetry affect the driving-point resistance and reactance as well as the radiation field.
- Does the 1:1 balun match the antenna? No. The radiator and radial geometry establish the nominal input. The balun controls common-mode current on the feedline exterior.
- Is one feedpoint height best at every site? No. Height must provide radial-tip clearance and suitable RF performance while accounting for ground, structures, safety and accessibility.
- Does a low SWR prove high efficiency? No. Match, radiation efficiency and realised gain are different quantities. Check loss, current and field behaviour separately.