VHF Radio Waves Research Articles

Atmospheric Effects on VHF and UHF Propagation

This paper is mainly concerned with the effects of the troposphere and ionosphere on the propagation of vhf and uhf radio waves. Tropospheric refractive index profiles and ionospheric electron density models representative of average atmospheric conditions are presented. Mathematical relationships are derived for calculating refraction effects, time delays, Doppler errors, polarization changes, and attenuation experienced by radio waves traversing the entire atmosphere.

Diurnal variations of signal level and scattering heights for VHF propagation

The scattering of VHF radio waves in the lower ionosphere is identified with turbulent fluctuations of the electron plasma. The theory of gradient mixing is applied to the afternoon and early evening periods, for which solar control is thought to dominate meteoric contributions. The scattering cross-section for this process, depends on ionospheric conditions only through the ambient electron density-height profile's gradient dN/dh. It is found that the afternoon decay of signal strength and simultaneous increase of scattering height can be correlated with independent estimates of electron density and recombination coefficients in the lower ionosphere. The observation of two scattering levels on short paths and the lack of a midday maximum on long paths is predictable. Diurnal variations of the frequency dependence of these transmissions suggest a strong influence of the earth's magnetic field.

Review of Ionospheric Effects at VHF and UHF

This paper summarizes the present-day knowledge of ionospheric effects at vhf and uhf, with the exception of forward scattering of vhf radio waves by the ionosphere. The seven effects covered in the paper are: Radar Echoes from Aurora, Radar Echoes from Meteors, The Faraday Effect and Radar Echoes from the Moon, Radio Noise of Auroral Origin, Absorption of Radio Waves by the Ionosphere, Refraction of Radio Waves by the Ionosphere, and the Scintillation of the Radio Stars. Each ionospheric effect has in turn been divided into separate subtopics, and the main results are given in these subsections, with particular emphasis upon providing references to the original papers. In this way the reader wishing to know the answer to a specific problem will speedily be able to find a summary of the main published results in the field, and also be able to learn which papers deal with the particular topic of interest.

Oblique-incidence measurements of the heights at which ionospheric scattering of VHF radio waves occurs

Indirect measurements of the heights at which ionospheric scattering of VHF waves occurs, using the technique of measureing the differences in the times of arrival of tropospheric and ionospheric pulses received over an 810-km oblique-incidence path, were made by the National Bureau of Standards in November 1952 and in January 1953. These measurements show approximate heights of 86 km and 70 km, respectively, for the night-time hours and the midday hours. The accuracy of the heights obtained in this way are subject to uncertainties about the actual tropospheric delays.

An Estimation of Diurnal Variation of VHF Radio Waves

An Estimation of Diurnal Variation of VHF Radio Waves