Long Path & Short Path Propagation

 

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Long-Path 

Long-path propagation, also known as "long-haul" or "long-distance" propagation, refers to the transmission of radio signals over long distances, typically over the horizon. This can happen when the radio signals are reflected or refracted by the ionosphere, a layer of charged particles in the upper atmosphere, which can cause the signals to travel much further than they would be able to travel in a straight line.

Long-path propagation is a common phenomenon in the High Frequency (HF) and Medium Frequency (MF) bands, which are used for long-distance communication, such as in Amateur Radio, Marine and Aeronautical communications, and Military communications.

Long-path propagation can be used to communicate over distances of thousands of kilometers, and it can be particularly useful in situations where other forms of communication are not possible, such as in remote or disaster-stricken areas. However, it can also be affected by various factors such as time of day, solar activity, and atmospheric conditions, which can cause the signal strength and quality to vary greatly.

When using long-path propagation, operators must be aware of the fact that due to the ionosphere's properties, signals may be reflected by different layers of the ionosphere at different angles, which can cause multiple signals to arrive at the receiving station at the same time. This phenomenon is known as "multi-hop" propagation, and it can cause severe fading and distortion of the received signal.

Short-path propagation, also known as "short-haul" or "short-distance" propagation, refers to the transmission of radio signals over relatively short distances, typically within the line of sight of the transmitting and receiving antennas. This happens when the radio signals travel in a straight line between the antennas, without any significant reflection or refraction by the ionosphere or other atmospheric layers.

Short-Path 

Short-path propagation is most commonly found in the Very High Frequency (VHF) and Ultra High Frequency (UHF) bands, which are used for local and regional communication, such as in two-way radios, television and FM radio broadcasting, and mobile communications.

Short-path propagation is generally more reliable than long-path propagation, as the signal does not have to travel through the ionosphere and is less affected by atmospheric conditions. However, the distance that can be covered is limited by the line of sight and typically ranges from a few kilometers to a few tens of kilometers, depending on the terrain and the height of the antennas.

In addition, when using Short-path propagation, the signal can be blocked by obstacles such as buildings and hills, which can cause "shadowing" or "dead zones" in the coverage area. To overcome these issues, repeaters and other signal amplification systems can be used to extend the coverage area or to provide a clear signal in areas where it may be obstructed.