# Half Wave Dipole Antenna

1/2 Wavelength Dipole Antenna Calculator

Speed of Light = 299,792,458 m/s = 300 = s

Frequency = Operating Frequency in MHz = fo

Velocity Factor (see text*) = constant for 50 ohms cable = 0.95

Results is in meter…..

Meter -> Inch = 1 meter = 39.3701 inches

Formula:

λ =  s / fo

Vertical Monopole Element = (λ*0.5)*vf

Actual wavelength approximate rounding off to = 81.3990 or 81.4 inches

Substitute from the formula for 145.000 MHz

λ = s / fo (meters)
λ = 299,792,458 /145,000,000 = 2.0675 meters

λ =  = 2.0675 meters

Converting to inches by multiplying wavelength results to 39.3701

λ = 2.0675 x 39.3701 = 81.3990 inches

Hence:

λ = 81.4 inches = L

vf = 0.95

Solving for one-half wavelength:

Radiating Element = (λ*0.5)*vf  = E

= (81.4 x 0.5) x 0.95 = 38.6645 inches

Divided by 2 elements for upper and lower elements

= 38.6645/2 = 19.3 inches

Gap between Radiating Element = λ / 200 = 0.407 inch = G

L = 81.4“

E = 19.3”

G = 0.407”

Note: important
Adjust To the lowest Standing Wave Ratio (SWR)

• Check SWR, using SWR/Power Meter, tune to Operating Frequency (e.g. 145.00MHz)
• Connect cable. Antenna -> SWR/Power Meter -> Radio
• Set to SWR / Power to test
• Hence: if SWR = 1-1.2, Power = Radio Power Output Set, if you set your radio power to 5 watts it should be 5 watts meter reading in the SWR/Power meter.
• If the measurements of the cut elements are correct for the Operating Frequency, fixed and finalized antenna, else if the results reading is/are not meet the ideal reading, cut both elements.

Cutting:

• Operating Frequency = 145.000 MHz
• If the SWR is high and Power is low
• Adjust radio frequency to either higher or lower frequency to read to the lowest SWR, take note the Frequency with the lowest SWR
• Now, example the frequency with the lowest SWR is 146.000 MHz
• New formula New Frequency divided by old Frequency multiple by original radiating element results.

= (146 / 145) x 20.265

= 20.125 inches

BY: Nicolas C. Medalla, DW7NCM

HRC – Tribu Amihan