How Does Ground Wave Propagation Enable Reliable Radio Signals?
To understand the meaning of ground wave propagation, it is first important to understand the meaning of radio wave propagation,. Radio wave propagation can be explained as the radio waves which propagate from one point to another or into various parts of the atmosphere.
Depending upon the frequencies, these waves propagation can be classified as:
Ground waves propagation
Skywave propagation
Free space propagation
What is Ground Wave Propagation?
Ground Wave propagation is a method of radio wave propagation that uses the area between the surface of the earth and the ionosphere for transmission, it. Ground wave propagation is also called surface wave propagation. The ground wave follows the contour of the earth and hence it can propagate considerable distances. Such a wave is called a direct wave. It exists below the 2 MHz frequency range. Ground wave propagation over the earth's surface can be propagated to a considerable distance by the ground wave, in the low frequency and medium frequency portion of the radio spectrum. Ground waves are mainly used for transmission between the surface of the earth and the ionosphere. These are made up of the number of constituent waves. Low frequencies of the electromagnetic spectrum were used. The collection of these radiations along the surface of the earth is known as ground wave propagation. The intensity of these radiations drops with distance due to their absorption by ground.
It is known as a ground wave because it is the sum of the waves that are reflected by the earth’s surface or any hills. The curvature of the earth is being followed by the waves, enabling them to cover beyond the horizon. The waves get blocked beyond the horizon, by the curvature of the earth and the signals are produced by the diffracted surface wave.
Frequency of Ground Waves Depending on the Type of Ground:
Advantages of Ground Wave Propagation
As it uses lower frequencies, interference occurs due to atmospheric noise only. That's why the absorption of EM waves at lower frequencies is less. Hence it can cover longer distances. However, the path loss increases as the distance from the transmitter increases.
These waves are more efficient and also these are not affected by the change in atmospheric conditions, due to the bending around the corners or obstructions during propagation.
They are vertically polarized in order to prevent short circuits of the electric field (E) component.
Disadvantages of Ground Wave Propagation
High-frequency waves cannot be transmitted as the energy losses are more because of the absorption of energy in the earth’s atmosphere.
These are used to cover short ranges and also involve attenuation of waves as they interact with the eddy currents produced by the surface of the earth.
If the polarization of the ground wave is affected, E field components are short-circuited with the ground.
Applications Ground Wave Propagation
To provide the local radio communications coverage, we generally use ground wave propagation, especially by radio broadcast stations that are required to cover a particular locality.
Ground wave propagation can be used for one-way communication from the military to submerged submarines as they penetrate to a significant depth into seawater.
AM, FM, and television broadcasting can be done with the help of ground waves.
Ground wave propagation of radio signals is ideal for relatively short distance propagation on these frequencies during the daytime.
Fun Facts
The signal of ground wave propagation travels over the surface of the ground, and as a result, it is used to provide regional coverage on the long and medium wavebands.
To provide the local radio communications coverage, we generally use ground wave propagation, especially by radio broadcast stations that are required to cover a particular locality.
Ground wave propagation of radio signals is ideal for relatively short distance propagation on these frequencies during the daytime.
Ground wave propagation of the wave follows the contour of the Earth. Such a wave is called a direct wave. Due to the Earth’s magnetic field, the wave bends and gets reflected in the receiver. Such a wave can be termed as a reflected wave.
The wave that propagates through the Earth’s atmosphere is known as a ground wave. The signal at the receiver station is being contributed by the direct wave and reflected wave together.
FAQs on Ground Wave Propagation Explained: Concepts, Uses & Limitations
1. What is ground wave propagation and how does it work?
Ground wave propagation, also known as surface wave propagation, is a method of radio wave transmission where electromagnetic waves travel along the surface of the Earth. It works by following the curvature of the planet. As the wave propagates, it induces currents in the ground, which allows the wave to be guided along the surface. This mode is most effective for low and medium frequencies because higher frequency waves are absorbed more quickly by the ground.
2. What is the effective frequency range for ground wave propagation?
The effective frequency range for ground wave propagation is in the Low Frequency (LF) and Medium Frequency (MF) bands, typically from a few kilohertz (kHz) up to about 2-3 MHz. Frequencies above this range suffer from high attenuation as the energy is absorbed by the Earth's surface, making this mode of propagation inefficient for high-frequency signals.
3. What are the primary applications of ground wave propagation?
Ground wave propagation is highly reliable for short to medium-distance communication due to its stable signal path. Its primary applications include:
- AM radio broadcasting: Local and regional AM stations use this method to provide consistent coverage.
- Maritime communication: It is used for ship-to-shore and ship-to-ship communication.
- Navigational aids: Certain radio navigation systems rely on the predictability of ground waves.
- Military communication: It is used for short-range tactical communications where reliability is crucial.
4. How does ground wave propagation differ from skywave and space wave propagation?
The three main modes of propagation differ in their path, frequency, and use:
- Ground Wave Propagation: Travels along the Earth's surface. It's used for low frequencies (up to 2-3 MHz) and provides stable, short-range communication like AM radio.
- Skywave Propagation: Waves are reflected off the ionosphere to travel long distances. It's effective for higher frequencies (3 MHz to 30 MHz) and is used for international shortwave broadcasts. Its range depends on atmospheric conditions.
- Space Wave Propagation: Travels in a straight line from the transmitter to the receiver (line-of-sight). It's used for very high frequencies (VHF/UHF) like FM radio, TV broadcasting, and satellite communication.
5. What key factors limit the range of ground wave propagation?
The range of ground wave propagation is primarily limited by attenuation, which is the loss of signal strength as it travels. The main factors causing this are:
- Frequency of the wave: Attenuation increases significantly with higher frequencies. This is the primary reason it's not used for signals above 3 MHz.
- Conductivity of the Earth's surface: The wave travels much farther over surfaces with high conductivity, like seawater, compared to poor conductors like dry, sandy land.
- Tilting of the wavefront: As the wave moves over the Earth, the lower part of the wavefront is slowed down by the ground, causing the wave to tilt forward and lose energy.
6. Why must ground waves be vertically polarised to propagate effectively?
Ground waves must be vertically polarised because of the electrical properties of the Earth's surface. The Earth acts as a conductor. If the wave's electric field were horizontal, the conductive ground would short-circuit the electric field, causing the signal's energy to be dissipated almost immediately. With vertical polarisation, the electric field is perpendicular to the ground, preventing this short-circuiting effect and allowing the wave to propagate along the surface.
7. Why is ground wave propagation unsuitable for high-frequency TV and FM broadcasts?
Ground wave propagation is unsuitable for high-frequency signals like those used for TV (VHF/UHF) and FM radio because these signals experience extremely high absorption by the ground. At these frequencies, the energy of the wave is rapidly dissipated into the Earth as heat, leading to severe attenuation and a very short communication range. Therefore, TV and FM signals rely on space wave (line-of-sight) propagation, which requires a direct, unobstructed path between the transmitting and receiving antennas.
