Antenna Length Calculator (lambda/4)

Calculates antenna element lengths based on the relationship between frequency and wavelength. Antennas must be proportional to the wavelength of the signal they transmit or receive. Worked example: a quarter-wave vertical for 145 MHz is 71.25/145 = 0.49 m, times 0.95 velocity factor = 46.8 cm. For a 2.4 GHz WiFi whip: 71.25/2450 = 2.9 cm, about 2.8 cm after the factor. Insulated wire needs trimming: its velocity factor of 0.90-0.95 means a calculated 49 cm whip actually resonates around 47 cm, so cut long and trim while watching an SWR meter for the dip.

1. 1

   Step 1

   Enter the operating frequency

2. 2

   Step 2

   Select the antenna type (dipole, monopole, or loop)

3. 3

   Step 3

   View calculated wavelength fractions

4. 4

   Step 4

   Apply velocity factor for wire antenna construction

• 1

  Half-wave dipole is the most common antenna type

• 2

  Quarter-wave monopole needs a ground plane to work

• 3

  Apply 0.95 velocity factor for copper wire antennas

• 4

  Higher frequency = shorter antenna length

• Forgetting to apply the velocity factor for real conductors

• Not accounting for surrounding objects affecting performance

• Building antennas too close to metal structures

• Confusing electrical length with physical length