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It is necessary to define radio wave propagation in order to comprehend the meaning of skywave propagation. The behaviour of radio waves as they spread from one location to another or into different areas of the atmosphere is known as radio wave propagation.
The categorisation of these waves is as follows:
1.The propagation of ground waves
2.The transmission of skywaves
3.Propagation in free space
Skywave propagation
The skywave propagation is a kind of radio wave propagation. The ionosphere, which is an electrically charged layer of the upper atmosphere, either reflected or refracted back waves to the earth.
Medium and shortwave frequencies can be refracted back to earth beyond the horizon, making them useful for wave transmission over continents. The table below shows the distribution of MUF (maximum usable frequency) and OWF (optimum working frequency) frequencies based on the earth’s layers:
Purpose of Sky Wave Propagation
We explored ground wave propagation in the above paragraph, which is when an electromagnetic wave travels through the earth’s surface. We already know that ground wave propagation is usually ideal for low-frequency electromagnetic signal transmission (usually up to 2 or 3 MHz).
Another significant disadvantage of ground wave propagation is that it is only suitable for short-range operation. Because the induced wave produces attenuation of the propagating signal in ground wave propagation, this is the case. As a result, in the case of ground wave propagation, it is preferable to send the signal over short distances in order to achieve the lowest attenuation.
The two fundamental disadvantages associated with ground wave propagation are low-frequency signal transmission and short-distance propagation. Sky wave propagation is employed in order to solve these two drawbacks.
- It enables for the transmission of higher-frequency electromagnetic waves over longer distances than ground wave propagation.
- It accomplishes this through ionosphere-based wave reflections. Ionospheric wave propagation is the name given to this phenomenon.
Critical Frequency
The critical frequency is the highest frequency at which 100% internal reflection from the ionosphere occurs. The following is the mathematical representation:
fc=9√Nmax
Where,
Fc stands for critical frequency in Hz.
Nmax is the maximal electron density per cubic metre.
The critical frequency fluctuates based on the weather, the time of day, and the angle at which the antenna fires the radio waves.
Skip distance
The minimal distance between the earth’s surface and the location from where the radio signal is broadcast is known as the skip distance. The skip distance for a flat earth is:
DSKIP=2h√[(fMUF/fc)²-1]
Where,
DSKIP is the abbreviation for “distance skipped.”
h : the height at which the reflection occurs
fMUF stands for “maximum usable frequency.”
fc stands for crucial frequency.
Applications of Sky Wave Propagation
1.As we know satellite communications are dependent on upper atmospheric conditions in which skywave propagation is used.
2.Communication with mobile devices
Space Wave Propagation
Space wave propagation refers to radio waves that occur within 20 kilometres of the troposphere, and includes both direct and reflected waves. Because these waves can move directly from the earth’s surface to the troposphere’s surface, they are also known as tropospheric propagation. Because the signals are carried in a straight path from the transmitter to the receiver, it is also known as line of sight propagation.
The height of the antennas and the spacing between them can be given as follows to avoid attenuation and loss of signal strength:
Dm=(2RHt)-½+(2RHr)-½
Where,
Dm stands for the distance between the two antennas.
R is the earth’s radius.
Ht : antenna transmission height
Hr : receiver antenna height
Application of Space Wave Propagation
It’s utilised in a variety of communication systems, including
1.Line-of-sight communication and satellite communication are two types of communication.
2 Communication using radar
3.Linking with microwaves
4.Limitations on the propagation of space waves
5.The curvature of the globe has an impact on these waves.
6.These waves propagate along the line of sight distance, which is defined as the distance between the transmitting antenna and the receiving antenna, also known as the communication range.
Conclusion
We may conclude that skywave, which takes advantage of the ionosphere’s reflecting properties at higher frequencies above the earth, is the most straightforward mode of propagation and provides ongoing assistance in communications. In similar manner as a result, we can deduce that the propagation of space waves is limited to the line of sight distance, which is defined as the distance between the transmitting and receiving antennas at which both can see each other.
