Refraction of short radio waves in the upper atmosphere

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The paper shows that the striking phenomena of short-wave radio transmission (i.e., below 60 meters) can be quantitatively accounted for on a simple electron refraction theory in which the effect of the earth's magnetic field and electron collisions may be neglected as a first approximation. The distribution and number of electrons per unit volume in the upper atmosphere required on this theory to account for the meager experimental data appear to be in general accord with the values required in the explanation of the diurnal variations of the earth's magnetic field, aurorae and long-wave radio transmission. The paths taken by the waves from an antenna to distant points on the surface of the earth are calculated. The path calculations give a definite picture of the now familiar skip distance effects. Ideal signal intensity curves (i.e., neglecting absorption and scattering) are given, which show how the energy sent out by a transmitter is distributed over the surface of the earth. A focussing of energy just beyond the skip distance, and again just inside the point where the ray tangent to the ground at the transmitter comes back to earth is clearly shown. The reflection of waves at the surface of the earth is also considered. The results of these calculations make it possible to estimate the most suitable wave lengths for night and day communication between any two points on the earth's surface. It is also pointed out that there will be a minimum wave length, in the vicinity of 10 meters, below which long distance communication becomes impossible. It is shown that from the point of view of long distance communication low angle radiation is most effective. The ray paths and energy flux density in the wave front of the sky waves are independent of the plane of polarization of the transmitter. The effects of polarization on the reception problem are not discussed.