Characteristics of the earth-ionosphere waveguide for VLF radio waves

The principal results of this technical note are graphical presentations of the attenuation rates, phase velocities, and excitation factors for the dominant modes in the earth-ionosphere waveguide.The frequency range considered is 8 kc/s to 30 kc/s.The model adopted for the ionosphere has an exponential variation for both the electron density and the collision frequency, and the effect of the earth's magnetic field is considered.Comparison with published experimental data confirms that the minimum attenuation of VLF radio waves in daytime is approximately at 18 kc/s, while at night it is somewhat lower.The directional dependences of propagation predicted by the theory are also confirmed by experimental data.1.