Calculate efficiency of vertically polarised antenna from far field strength


This calculator allows calculation of the efficiency of a short / small vertically polarised antenna from field strength measured near ground level in the far field.

Frequency (MHz)
Power input (W)
Ground conductivity (S/m)
Ground relative permittivity
Distance (m)
Measured field strength (dBµV/m)
cmf (V)
b (°)
|As| (dB)
Efficiency (%)
Efficiency (dB)

Use Directivity=3.0 for short monopoles and small loops. Some other Directivity values for common monopole heights over perfectly conducting earth are λ/4=3.3, λ/2=4.9, 5λ/8=6.3.

If the calculator reports "check inputs", the scenario is not possible, or not capable of accurate calculation.

The calculator uses Norton's f5 approximation for ground wave attenuation.

Example 1 is from (Belrose 1998) mobile whip on 7MHz. It Belrose's base data point from the curve fit of Fig 2, and yields a higher efficiency than Belrose calculated because he appears to have ignored factor |As| which is 0.8176.... his antenna is probably nearly 2dB more efficient than he calculated.

Example 2 is from (Griffith 1987).

Example 3 is from (Boswell et al 2005) 1m loop on 3.6MHz. It is one data point from Fig 6, and yields almost identical efficiency to Boswell's Table 2.

References / Links


Version Date Description
1.01 22/11/2015 Initial.

© Copyright: Owen Duffy 1995, 2021. All rights reserved. Disclaimer.