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.
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.
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