Last Updated on May 13, 2026 by John Berry
I’ve described here the nature and magnitude of the effects of vegetation, buildings, and rain and therefore how radio amateurs might think about them. I’ve written it as some general guidelines, rather than describing any specific method of treatment.
My image below shows the typical scenario. The path could also be via the ionosphere, satellite, meteor trail, aurora or the Moon or other medium. The same principles apply.
Vegetation
Broadly, any obstacle intruding into a radio path (as outlined on my page on the Fresnel zone) should be included within the path profile and assumed as an opaque obstruction. Thus, a single tree would appear as a knife edge and a forest would add to the roundness of obstructions as if the terrain was pushed up to the forest height. I describe elsewhere how propagation by diffraction enables obstructed paths.
The degree of obstruction must also be considered laterally across the path. A wide forest (relative to the Fresnel zone) will attenuate more than a narrow group of trees. And you can see the greatest effect in the foreground of the station where the relative obstruction size is most significant.
That’s clearly all worst case, applying above about 430MHz. Between about 20MHz and 430MHz the effect of vegetation depends a lot on the leaf size. Hence, in winter, deciduous trees would have little effect. In summer, however, their effect in the foreground of the station could add anything from a few dB to tens of dB to the path loss. Whether this matters over specific paths depends on the path budget.
The effect of vegetation also varies with time and locations. As a result, vegetation may have a considerable effect most of the time, but during lift conditions for small percentages of time, the effect may be low. It’s all in the geometry.
Vegetation has little effect on propagation below about 20MHz. It may have other effects when close to LF/MF/HF antennas, for example.
The typical mitigation of path loss due to vegetation is to elevate the antenna to reduce the loss due to the path obstruction.
Buildings
It’s easier to visualise buildings as a complete block impinging the Fresnel zone. Simply, there’s no issue about the degree of opacity. Unlike some vegetation, buildings are definitely opaque! If a building is in the path, it can be modelled as a knife edge or as a rounded obstruction adding anything from a few dB to tens of dBs to the path loss.
Like trees, the degree of obstruction must also be considered laterally across the path. And the greatest effect is seen in the foreground of the station where the relative obstruction size is more significant.
Buildings have little effect below about 20MHz.
The typical mitigation of buildings in the path profile is to elevate the antenna to reduce the loss.
Rain
By rain here, I include rain, hail, snow, mist, and cloud. This group is known as hydrometeors.
Very broadly, the degree of hydrometeor attenuation depends on the size of the droplets and the density and size of the hydrometeor cloud.
Generalising, hydrometeors add little to path loss below about 10GHz. Even around 10GHz, it takes a heavy rain rate like 50mm/hr with large rain drops in a large rain cell to cause a significant path outage. A 50mm/hr rate occurs in the UK for small percentages of time, even on the west of Scotland.
For those inclined, there has been much published on how rainfall affects microwave links – and more recently on how to use microwave links to estimate raindrop size.
For radio amateurs, hydrometeors are more interesting as a source of anomalous propagation via rain scatter at above 10GHz.
Effects of vegetation buildings and rain
Vegetation, buildings, and rain have varying effect on radio amateurs’ enjoyment. Buildings and summer vegetation have greatest effect in the foregrounds of stations. Mitigation is increased antenna height.
Rain and other hydrometeors have little effect on propagation below about 10GHz.
Lower three vector Illustrations by Public domain vectors on Unsplash