Comms 3 (MOD 2) Flashcards
Types of waves
- mechanical
- electromagnetic
Types of mechanical waves
- transverse
- longitudinal
A wave that is an oscillation of matter and is responsible for the transfer of energy through a medium.
Mechanical wave
A wave created by a fusion of electic and magnetic felds
Electromagnetic wave
are wave from the portion of electromagnetic spectrum at lower frequencies than microwaves.
Radio waves
Radio waves travel at the speed of
Light
is the behavior of radio waves as they travel or are propagated from one point to another into various parts of the atmosphere
Wave propagation
Radio waves properties
- can’t be felt or touched
- travel long distance/speed of light
- reflection, refraction, absorption, diffraction
- emitted by objects with changing magnetic field
involves change in direction of waves when they bounce off a bartier.
Reflection
the bending of the path of the waves, involves a change in the direction of waves as they pass from one medium to another.
Refraction
change in direction of waves as they pass through an opening or around a barrier in their path.
Diffraction
act as a waveguide for electromagnetic wave propagation.
Earth/ionosphere
- 3 kHz to 30 kHz
- highly vulnerable to disturbance
- easily gets distorted by atmospheric changes.
- Scientists use this frequency band in seismic studies
Very Low Frequency (VLF)
- 30 kHz to 300 kHz.
- Suitable for long-distance communication.
- Has less attenuation from big terrains
Low Frequency (LF)
- 300 kHz to 3 MHz
- follows the curvature of the Earth
- cover regional distances,
Medium Frequency (MF)
- 3 MHz to 30 MHz
- known for its skywave propagation
- ideal for long-distance communication
High Frequency (HF)
- 30 MHz to 300 MHz
- most commonly used bands.
- usually affected by big terrains but is suitable for short-distance communication.
Very High Frequency (VHF)
- 300 MHz to 3 GHz
- most important frequency band for modern wireless communication systems.
- signals generally require a direct line of sight.
Ultra High Frequency (UHF)
- 3 GHz to 30 GHz.
- can only operate in a line of sight path.
- It is commonly used in point-to-point communication
Super High Frequency (SHF)
- 30 GHz and 300 GHz.
- only used in advanced communication systems
- is used in radio astronomy and remote sensing
Extremely High Frequency (EHF)
Three principle paths of radio waves
- ground wave
- sky wave
- space wave
a method of radio wave propagation that uses the area between the surface of the earth and the ionosphere for transmission.
Ground wave
A type of radio wave communication in which the electromagnetic wave propagates due to the reflection mechanism of the ionospheric layer of the atmosphere.
Sky wave
Defined for the radio waves that occur within the 20km of the atmosphere, consisting of a direct and reflected wave
Space wave
It is also known as a line of sight propagation
Space wave
Advantages of Ground Wave Propagation
- Large wavelength/Less attenuation
- Signal loss is less
Disadvantages of Ground Wave Propagation
- Transmitters and Receiver must be close
- operational frequency range is limited to up to 2MHz
Advantages of sky wave propagation
- Large distance propagation
- Frequency range is high
- attenuation is less
Disadvantages of sky wave propagation
- Long-distance propagation requires large-sized antennas
- variation in signal transmission
Disadvantage of space wave
Obstacle causes attenuation
Structure of ionosphere
- D
- E
- F1
- F2
Length of ionosphere
60-400km
due to ___ on the atmosphere, EM wave gets reflected back towards the surface of the earth
Ionization
A type of radio wave communication in which the electromagnetic wave propagates due to the reflection mechanism of the ionospheric layer of the atmosphere.
Sky wave
Defined for the radio waves that occur within the 20km of the atmosphere, consisting of a direct and reflected wave
Space wave
a method of radio wave propagation that uses the area between the surface of the earth and the ionosphere for transmission.
Ground wave
