# Calculate efficiency of vertically polarised antenna from far field strength

***EXPERIMENTAL***

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.

 Inputs: Frequency (MHz) Power input (W) Ground conductivity (S/m) Ground relative permittivity Distance (m) Measured field strength (dBµV/m) Directivity Results: cmf (V) p b (°) |As| |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.

• Belrose, J. Sep 1998. A tuneable all bands HF camp/mobile antenna In Communications quarterly Fall 1998.
• A Boswell, A Tyler, and A White. Apr 2005.  Performance of a small loop antenna in the 3-10 MHz band In IEEE Antennas and Propagation Magazine, Vol. 47, No. 2, April 2005.
• Griffith, J. Mar 1987. Radio wave propagation and antennas - an introduction. Prentice Hall.
• Norton, KA. Dec 1941. The calculation of ground wave field intensity over a finite conducting spherical earth. Proc IRE, vol 29, pp 623-639.
• ———. Oct 1936. The propagation of radio waves over the surface of the earth and in the upper atmosphere  Part I. Proc IRE, vol 24, pp 1367-1387.
• ———. Sep 1937. The propagation of radio waves over the surface of the earth and in the upper atmosphere  Part II. Proc IRE, vol 25, pp 1203-1236.
• Ronlong Li. Jul 1983. The accuracy of Norton's empirical approximations for ground wave attenuation In IEEE transactions on antennas and propagation Jul 1983 pp 624-628.

# Changes

 Version Date Description 1.01 22/11/2015 Initial. 1.02 1.03 1.04 1.05