How to make 5/8 λ Vertical Antenna

| February 20, 2026 | Amateur Radio (Ham Radio) | No Comments

Building a 5/8 λ vertical antenna is a classic project for radio amateurs looking for a low angle of radiation, which is excellent for DX (long-distance) communication. Unlike a standard 1/4 λ vertical, this design provides about 1.5 to 3 dB of gain, though it requires a matching network because its natural impedance is not 50 Ω.

Calculating the Element Length

The physical length of the radiator is the most critical part. To calculate the length in meters, use the following formula:

L = 300/f x 0.625 x v

  • f: Frequency in MHz.
  • 0.625: Represents the 5/8 wavelength.
  • v: Velocity factor (usually 0.95 to 0.97 for aluminum tubing or wire).

Example for 20 meters (14.2 MHz):

L = 300/14.2 x 0.625 x 0.95 ~ 12.54 m

The Matching Network (Inductive Loading)

A 5/8 λ antenna is non-resonant and presents a high capacitive reactance at the base. To make it work with your coax, you must cancel that capacitance with an inductor (coil) in series at the base.

Connect a coil between the antenna element and the center conductor of your coax. The shield of the coax goes to the ground/radials. Tap the coax center conductor a few turns up from the ground to find the 50 Ω point.

The Ground System (Radials)

For a vertical antenna to perform efficiently, it needs a “mirror” or a counterpoise.

  • At Ground Level: Use at least 16 to 32 radials (the more, the better) buried slightly or laid on the grass.
  • Elevated: If mounting on a pole, use at least 4 tuned 1/4 λ radials (5.02m for 20m band) sloping downwards at a 45-degree angle.

Construction Steps

  1. Prepare the Radiator: Use telescoping aluminum tubing for rigidity. If it’s a wire antenna, hang it from a tall tree or a fiberglass pole.
  2. Insulate the Base: Ensure the bottom of the radiator element is insulated from the ground or the mounting mast.
  3. Winding the Coil: 8-10 turns of 12 AWG enameled copper wire on a 2 inch PVC pipe gives around 2 μH inductance.
  4. Tuning: Use an SWR meter or an antenna analyzer.
    • Adjust the coil (add/remove turns or move the tap) to find the lowest SWR. Tap can be at 3 turns to start with. Change the tap position about half a turn in each tuning step. A thick crocodile clip can be used for checking and once the best SWR is found, the tap can be soldered in place.
    • If the SWR is still high, slightly adjust the physical length of the radiator.