VHF Propagation Research Articles

A Review of VHF Ionospheric Propagation

Although the very high frequencies (vhf,30-300 mc) are allocated for utilization almost entirely upon the premise that propagation will be tropospheric, there are very definite ionospheric effects with which one must reckon. These are: (1) regular F2 ionization, (2) sporadic E ionization, (3) scattering from regular ionization, (4) auroral ionization, (5) meteoric ionization. The first of these is predictable with reasonable accuracy and provides phenomenally good communication over great distances and with extremely low power. The second is far less predictable, but it also can provide good communication with extremely low power. The third is mainly a newly discovered phenomenon; although it offers intriguing possibilities for regular communication, it presents at the same time large problems in achieving that end. The fourth and fifth are so far only of nuisance value to the communicator. However, they are phenomena of great interest to the geophysicist, as indeed are the other phenomena as well. In this paper, the nature of vhf propagation arising from these sources of ionization is discussed. The maximum distance between path terminals for single-hop propagation is, of course, about 2,400 km for reflection from E region effects and about 4,000 km for F region effects. Multiple hops are rarely significant except from the regular F2 ionization at frequencies only slightly above 30 mc. A considerable amount of information is included on the nature of the ionization as deduced from the propagation effects. The work of individual investigators is extensively referenced.

Meteorological effects on VHF propagation

Meteorological effects on VHF propagation

A New Kind of Radio Propagation at Very High Frequencies Observable over Long Distances

The discovery and some results of a preliminary investigation of a new type of weak vhf propagation by means of the ionosphere is reported. This form of propagation appears to be observable over ranges out to about 2000 kilometers from the transmitter but is likely to be masked by other kinds of propagation at distances much less than about 1000 kilometers. The initial experiments on a frequency of 49.8 Mc/sec reveal the uninterrupted presence of observable signal over a test path of 1245 kilometers, irrespective of season, time of day, or geomagnetic disturbance, though showing dependence in intensity on these factors, and possibly on the meteor activity as well.Some preliminary speculations suggest that the mechanism of this type of propagation may be scattering caused by ever-present irregularities in the $E$ region, and an approximate transmission equation is derived in terms of parameters describing inhomogeneities in the $E$ region. Measured signal intensities during periods of hf radio fadeouts associated with solar flares never show any reduction in signal. On the contrary, there is usually an enhancement of signal intensity accompanied by a simultaneous weakening of the background noise. This result suggests strongly that the signals are returned from a part of the $E$ region near or just below the absorption region for ordinary hf radio waves.