Effect of Wooded Channels on 519.25-MHz UHF Radio Wave Propagation

Abstract

The effect of vegetation on 519.25-MHz UHF radio wave propagation was investigated in wooded areas of Calabar, located in Cross River State, Nigeria. The primary objective of the study was to collect statistical data on signal strength at various depths within forested channels, in order to evaluate signal losses caused by vegetation. Measurements were taken using a digital Cable Television (CATV) meter/analyzer (Model DLM3-T) connected to a 4-meter-high slot receiver antenna. During each measurement, the receiver antenna was carefully adjusted to achieve the best possible signal quality, as displayed on the CATV analyzer screen, before recording the signal strength. All measurements were taken on the downlink only. The results indicate that significant UHF signal loss occurs when the height of the transmitting antenna exceeds the average tree height in a wooded area. This loss is primarily due to the obstruction caused by the canopy—comprising both foliaged (leaf-covered) and non-foliaged (bare-branched) sections—which interferes with end-to-end communication. It was also found that signal loss patterns are more strongly influenced by the type and density of vegetation than by the depth of the wooded channel. Furthermore, a noticeable discrepancy was observed between the measured signal losses and predictions made by the early ITU model, highlighting its limitations in such environments. Seasonal variations also played a significant role, with greater signal losses recorded during the rainy season due to denser foliage compared to the dry season, when vegetation was sparser.