Antenna Calculator
Calculate antenna dimensions for any frequency
MHz
Wavelength (Ξ»)
21.11 m (69.27 ft)
π Half-Wave Dipole
Total Length
32.96 ft (10.05 m)
Each Leg
16.48 ft (5.02 m)
Formula: 468 / f(MHz) = total length in feet
γ°οΈ End-Fed Half-Wave (EFHW)
Radiator Length
32.96 ft (10.05 m)
Counterpoise (10-15 ft typical)
10-15 ft (3-4.5 m)
Formula: 468 / f(MHz). Requires 49:1 transformer at feed point.
π‘ Quarter-Wave Vertical
Radiator Length
16.48 ft (5.02 m)
Ground Radial (each)
16.48 ft (5.02 m)
Formula: 234 / f(MHz) = length in feet
π² Full-Wave Loop
Total Wire Length
70.42 ft (21.46 m)
Per Side (Square)
17.61 ft (5.37 m)
Formula: 1005 / f(MHz) = total length in feet
π Quad Element
Driven Element
70.42 ft (21.46 m)
Reflector (+5%)
73.94 ft (22.54 m)
Director (-5%)
66.90 ft (20.39 m)
Square loop circumference
πΊ Yagi Elements
Driven Element
32.30 ft (9.85 m)
Reflector (+5%)
33.92 ft (10.34 m)
Director (-5%)
30.69 ft (9.35 m)
Based on half-wave element lengths
π J-Pole
Radiator (3/4Ξ»)
52.00 ft (15.85 m)
Stub (1/4Ξ»)
17.33 ft (5.28 m)
Gap
1.4 in (3.6 cm)
Matching stub J-pole antenna
β‘ 5/8 Wave Vertical
Radiator Length
41.20 ft (12.56 m)
Formula: 585 / f(MHz) = length in feet
πΆ Coax Lengths
1/4Ξ» (VF 0.66)
11.49 ft (3.50 m)
1/2Ξ» (VF 0.66)
22.98 ft (7.00 m)
RG-58, RG-8X (VF=0.66). For RG-213 (VF=0.66) same values.
Antenna Building Tips
Cut Long, Trim Slowly: Always cut wire 3-5% longer than calculated. Trim 1/2" at a time, checking SWR after each cut. You can't add wire back!
Height Matters: Dipoles perform best at 1/2 wavelength or higher above ground. Lower heights favor NVIS (near-vertical) propagation.
Ground Radials: For verticals, more radials = better performance. 4 radials minimum, 16-32 is ideal, 120 is perfect.
Wire Type: Use stranded wire for flexible installations. Solid copper works for permanent setups.
EFHW Tips: Use a 49:1 transformer (UnUn). A short counterpoise (10-15 ft) helps with RF grounding. Great for portable ops!
Trim for SWR: Cut equal amounts from both dipole legs. For EFHW, trim from the far end only. Re-measure after each trim.