1/r attenuation

Hello all,

I did some reading on radio-theory (ground-waves) and yes, they do have
1/r attenuation with limitations. The book (finnish)  has graphs of
measurements on different frequencies and roughly the attenuation is 1/r
up to 10000km with 10kHz and only up to 10km with 200kHz - after this
distance the attenuation will change to greater - the measurent used 1kW
transmitter with vertical antenna. With 10kHz at 1km field-strengt 5E5
uV/m and at 1000km 4E2 uV/m. All values from graph that has distance as
x-axis and attenuation and field-strength at y-axis, semi-dry earth. All
the graphs for sea-water, moist earth, semi-dry earth as medium for waves
were quite similar at low-frequencies but the attenuation at higher
frequencies got a lot smaller when conductance was greater - 1/r up to
100km with 1Mhz and about 300km with 200kHz. 

The book mentiones that the first part of the attenuation graph is
according to Van Der Pol -law and the rest according to Fock&Wait -theory.
There's also lots of mathematics about calculation of these things. 

The chapter on this subject lists following references:

H.M.Barlow, J. Brown : Radio surface waves, Clarendon Press, 1962

H.Bremmer : terrestrial radio waves, Elsevier, 1948

R.J.King, J.R.Wait : Electromagnetic groundwave theory and
experiment, Symposio mathematica, Vol. XVIII, pages 107-208,
Academic Press, 1976

P.Knight, J.A.W.Robson : Empirical formula for groundwave
field-strength calculation, Electronic letters, Vol. 20,
No. 18, pages 740-741, Aug. 1984

J.Laiho : Measuring effective ground conductivity by measuring
field-strengths of RF fields, TKK, 1975 (Finnish)

S.Rotheram; Ground wave propagation, The Marconi Review,
Vol. XLV, No. 224, pages. 18-48, 1982

The book where the information above is present is "Radioaaltojen
eteneminen" (Finnish, translates to "Propagation of RF waves"), written
by I.V. Lindell.

I hope this helps someone out there,

  Kristian Ukkonen.

| Kristian Ukkonen       |  Do as thou wilt shall be the whole of the law |
| kukkonen-at-alpha.hut.fi  |_____  Chance favours the prepared mind  |-------
| http://www.hut.fi/~kukkonen |  Fear is the mind-killer  |---------
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