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Post a LessonAnswered on 07 Apr Learn Unit 10-Communication Systems
Nazia Khanum
Microwaves are a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter, shorter than those of radio waves but longer than those of infrared radiation. They are generated through the interaction of electric and magnetic fields. The primary methods for producing microwaves include:
Magnetron: The most common method of generating microwaves is using a device called a magnetron. A magnetron consists of a vacuum tube with a cathode, an anode, and a series of resonant cavities. When a high voltage is applied between the cathode and the anode, electrons are emitted from the cathode and accelerated towards the anode. These electrons then interact with the resonant cavities and a magnetic field, causing them to spiral and generate microwave radiation.
Klystron: Klystrons are vacuum tubes that can generate and amplify microwave signals. They work by accelerating electrons through a series of electrodes and then passing them through resonant cavities. As the electrons pass through the cavities, they interact with microwave-frequency oscillations, causing them to generate microwave radiation. Klystrons are often used in high-power applications such as radar and particle accelerators.
Traveling Wave Tube (TWT): TWTs are another type of vacuum tube used for generating and amplifying microwave signals. They work by passing an electron beam through a helical coil called a "slow-wave structure." As the electron beam travels through the coil, it interacts with microwave-frequency electromagnetic waves, causing it to generate microwave radiation. TWTs are often used in communication satellites and microwave amplifiers.
Solid-state devices: Solid-state devices such as Gunn diodes and IMPATT diodes can also generate microwaves. These devices rely on the properties of semiconductor materials to generate microwave radiation when subjected to high voltages or currents. Solid-state microwave sources are commonly used in applications such as microwave ovens and telecommunications.
These methods provide different advantages and are used in various applications ranging from consumer electronics like microwave ovens to advanced radar and communication systems.
Answered on 07 Apr Learn Unit 10-Communication Systems
Nazia Khanum
Skywave propagation, also known as ionospheric propagation, is a method of radio wave propagation used in the transmission of radio signals over long distances via reflection from the ionosphere, a layer of charged particles in the Earth's upper atmosphere. When radio waves encounter the ionosphere, they can be refracted or reflected back to Earth, allowing them to travel beyond the line of sight.
The ionosphere consists of several layers of charged particles, primarily ions and free electrons, which vary in density and altitude depending on factors like time of day, season, and solar activity. When radio waves encounter these charged particles, they can be affected in various ways:
Refraction: Radio waves passing through the ionosphere can be bent or refracted due to changes in the density of charged particles at different altitudes. This bending allows the waves to follow the curvature of the Earth and reach distant locations beyond the horizon.
Reflection: Radio waves with frequencies below approximately 30 MHz (known as HF or high-frequency waves) can be reflected by the ionosphere back toward the Earth's surface. This reflection enables long-distance communication over thousands of kilometers, even across oceans.
Skywave propagation is widely used in long-distance communication, especially for amateur radio, international broadcasting, and military communications. However, it is subject to various factors such as the time of day, solar activity, and ionospheric conditions, which can affect the reliability and quality of the communication link. Additionally, skywave propagation is susceptible to interference and signal fading due to changes in ionospheric conditions.
Answered on 07 Apr Learn Unit 10-Communication Systems
Nazia Khanum
Ground wave propagation refers to the transmission of radio waves along or near the surface of the Earth. When a radio signal is transmitted, it spreads out in all directions. Ground wave propagation occurs when these radio waves travel close to the Earth's surface, typically within the first few kilometers. This mode of propagation is commonly used for medium-wave (AM) and long-wave radio transmissions.
There are two primary components to ground wave propagation:
Surface Wave: This is the portion of the radio wave that travels along the Earth's surface. It follows the curvature of the Earth and can propagate over considerable distances, especially at lower frequencies. Surface waves are affected by terrain, soil conductivity, and other factors.
Space Wave: This component involves a combination of direct waves that propagate straight from the transmitter to the receiver and reflected waves that bounce off the ground or other obstacles before reaching the receiver. Space waves are more dominant at higher frequencies and shorter distances.
Ground wave propagation is affected by various factors including frequency, terrain, atmospheric conditions, and the conductivity of the Earth's surface. It's used for broadcasting purposes due to its ability to provide relatively consistent coverage over large areas, especially in regions with challenging terrain where line-of-sight transmission may be obstructed. However, it has limitations in terms of range and susceptibility to interference from other sources.
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Asked on 06/12/2021 Learn Unit 10-Communication Systems
Answered on 24/05/2021 Learn COMMUNICATION SYSTEMS
Dr. Sandeep Kumar Sharma
Associate Professor with 20 years of teaching experience.
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read lessAnswered on 16/10/2019 Learn Exercise 15
Swapna Shree
(b) Answer:
10 MHz
For beyond-the-horizon communication, it is necessary for the signal waves to travel a large distance. 10 KHz signals cannot be radiated efficiently because of the antenna size. The high energy signal waves (1GHz − 1000 GHz) penetrate the ionosphere. 10 MHz frequencies get reflected easily from the ionosphere. Hence, signal waves of such frequencies are suitable for beyond-the-horizon communication.
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Answered on 16/10/2019 Learn Exercise 15
Swapna Shree
(d) Answer:
Space waves
Owing to its high frequency, an ultra high frequency (UHF) wave can neither travel along the trajectory of the ground nor can it get reflected by the ionosphere. The signals having UHF are propagated through line-of-sight communication, which is nothing but space wave propagation.
read lessAnswered on 16/10/2019 Learn Exercise 15
Swapna Shree
Answered on 16/10/2019 Learn Exercise 15
Swapna Shree
Line-of-sight communication means that there is no physical obstruction between the transmitter and the receiver. In such communications it is not necessary for the transmitting and receiving antennas to be at the same height.
Height of the given antenna, h = 81 m
Radius of earth, R = 6.4 × 106 m
For range, d = (2Rh)½, the service area of the antenna is given by the relation:
A = πd2
= π (2Rh)
= 3.14 × 2 × 6.4 × 106× 81
= 3255.55 × 106 m2
= 3255.55
∼ 3256 km2
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Answered on 23/10/2019 Learn Exercise 15
Tasneem
Let ωc and ωs be the respective frequencies of the carrier and signal waves.
Signal received at the receiving station, V = V1 cos (ωc + ωs)t
Instantaneous voltage of the carrier wave, Vin = Vc cos ωct
At the receiving station, the low-pass filter allows only high frequency signals to pass through it. It obstructs the low frequency signal ωs. Thus, at the receiving station, one can record the modulating signal , which is the signal frequency.
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