Clarification of 3 transmission modes-Ground waves, direct waves, and sky waves.

[SUPERCASTER]

The primary transmission mode used for long waves and medium waves (broadcast AM) is ground waves, at higher frequencies ground wave propagation is minimal. Higher frequencies (such as VHF broadcast FM) primarily depend on direct wave propagation, and short wave (Ham, short wave broadcasting, etc.) usually depend on sky waves. The most favorable transmission modes differ according to wavelength (frequency) , as do transmission characteristics, attenuation, and range. Results do vary according to transmission mode and frequency. Calculating a transmission range at a given frequency for each of the three give differing results.
Here are some links that might be helpful to confused community broadcasters:
http://www.radio-electronics.com/info/propagation/ground_wave/ground_wave.php
http://en.wikipedia.org/wiki/Radio_propagation#Surface_propagation
http://www.its.bldrdoc.gov/programs...ky_wave/low_med_freq_ground_sky_wave_blue.pdf
Clearly shown are how medium wave (ground wave) transmission distances vary greatly depending on conditions and direction even with a non-directional monopole antenna with radial ground system. It can be seen that calculations and computer programs that depend solely on direct wave propagation can be widely in error when erroneously used to make predictions and incorrect limits for ground wave propagation.

 

[SUPERCASTER]

Here is another link showing the differences between various radio transmission modes. Obviously calculations are mode dependent. See diagram at bottom.
http://www.tpub.com/content/neets/14182/css/14182_75.htm

 

[rfry]

It can be seen that calculations and computer programs that depend solely on direct wave propagation can be widely in error when erroneously used to make predictions and incorrect limits for ground wave propagation.

Agreed, but as you point out, these really are mis-uses of those programs.

Just to note that the Part 15 AM coverage distances in the post linked below were made for the groundwave alone. As stated there, the numbers include the effects of ground conductivity as based on the FCC's medium-wave propagation curves and conductivity charts used for decades now by the commercial AM broadcast industry.

http://www.radio-info.com/smf/index.php/topic,43379.0.html

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