Long Distance PRSRadio Call
Over the last couple of months a couple of keen PRS Radio operators “Scott” ‘777’ and "Dave 820" based out of Christchurch have been thrilling our local operators by making regular long distance UHF calls exceeding 300km and succeeding in getting into our local PRS Radio Repeater based on the Western Hutt Hills overlooking Wellington.
These videos were shot in Wellington of the stations operating through the local PRS Channel 8 Duplex
Repeater.
Wellington - Christchurch
“Scott” ‘777’ (Christchurch) uses a 6 element yagi in v pol @10dbi mounted 10 meters off the ground and was operating from New Brighton Beach area
What Enables This to Happen?
Isotropic Ducting
In telecommunication, an atmospheric or Isotropic duct is a horizontal layer in the lower atmosphere in which the vertical refractive index gradients are such that radio signals are guided or ducted, tend to follow the curvature of the Earth, and experience less attenuation in the ducts than they would if the ducts were not present. The duct acts as an atmosphericdielectric waveguide and limits the spread of the wavefront to only the horizontal dimension.
Atmospheric ducting is a mode of propagation of electromagnetic radiation, usually in the lower layers of Earth’s atmosphere, where the waves are bent by atmospheric refraction. If operating over-the-horizon, ducting causes part of the radiated and target-reflection energy of the signal to be guided over distances far greater than the normal signal would travel. It also causes long distance propagation of radio signals in bands that would normally be limited to line of sight.
Normally radio "ground waves" propagate along the surface as creeping waves. That is, they are only diffracted around the curvature of the earth. This is one reason that early long distance radio communication used long wavelengths. The best known exception is that HF (3–30 MHz.) waves are reflected by the ionosphere.
The reduced refractive index due to lower densities at the higher altitudes in the Earth's atmosphere bends the signals back toward the Earth. Signals in a higher refractive index layer, i.e., duct, tend to remain in that layer because of the reflection andrefraction encountered at the boundary with a lower refractive index material. In some weather conditions, such as inversion layers, density changes so rapidly that waves are guided around the curvature of the earth at constant altitude.