VHF propagation beyond that of line-of-sight occurs by using the troposphere, the Ionosphere, or an obstacle such as the moon or a building.
There are three types of tropospheric propagation, or “tropo”, which take signals a significant distance beyond the horizon:
1. Enhanced tropospheric refraction occurs when there is a significant increase above the normal value of the refractive index in the atmosphere.
2. Tropospheric ducting occurs when radio waves are trapped within channels bounded by sharp changes in refractive index and…
3. Tropospheric scattering, which arises from small-scale variations in the refractive index.
These modes occur almost exclusively in the lowest few kilometres of the troposphere where the air density and water-vapour content are greatest.
It’s also worth noting that the refractive index decreases with height.
0:00 | Introduction
0:46 | The troposphere
1:20 | Refraction
1:54 | The most common VHF and UHF propagation
2:11 | The 3 types of Tropospheric Propagation
3:05 | Enhanced Tropospheric Refraction
4:00 | Tropospheric Ducting
4:12 | Surface Ducts
5:28 | Elevated Ducts
6:33 | Tropospheric Scatter
7:48 | Radiation Inversions
8:19 | Subsidence Inversions
10:20 | Aerological charts (BoM)
10:52 | Propagation prediction charts
11:12 | VKspotter
More at 3fs.net.au/tropospheric-propa...