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RF TOOLS // ANTENNA CALCULATOR

J-POLE DESIGNER

Calculate the dimensions for a high-performance J-Pole antenna.
Optimized for copper or aluminum tubing.

Calculation Parameters
Construction dimensions
① Radiator (3/4 λ)
54.06 cm0.541 m
② 1/4 λ stub
18.02 cm0.18 m
③ Feed point (from bottom)
3 cm
④ Insulating gap
1.48 cm
⑤ Total structure height
55.54 cm
Electrical specifications
Frequency: 405.800 MHz
Bandwidth (SWR≤2): 390 – 410 MHz
Impedance: ~50 Ω
Gain: ~3 dBd
Polarization: Vertical
Vf used: 0.975
⚠ Optimize the feed point (③) with an antenna analyzer.
Use a 1:1 choke balun to reduce common-mode currents.
Technical diagram J-Pole
④ 1.48 cm SO239 50 Ω COAX ▲ RF GND ① RADIATORE 54.06 cm 3/4 λ — 0.541 m ② STUB 18.02 cm 1/4 λ — matching ③ FEED POINT 3 cm dal basso stub RADIATORE 3/4λ STUB 1/4λ J-POLE // 405.800 MHz // Vf=0.975 ⑤ TOT 55.54 cm
① Radiatore 3/4 λ
② Stub 1/4 λ (matching)
③ Feed point 50 Ω
④ Gap isolante