COMMS3 (MOD 3) Flashcards
Transmission media is located
Below the physical layer
Computers use ___ to represent data.
Signals
Signals are transmitted in the form of
electromagnetic energy
2 classes of transmission media
- Guided
- Unguided
which are those that provide a conduit from one device to another
Guided media
Examples of guided media
- twisted-pair cable
- coaxial cable
- fiber-optic cable.
Design factors of guided media
- Bandwidth
- Transmission impairments
- Interference
- Number of receivers
One of the wires carries signal, the other is used only as a ground reference
Twisted pair
In twisted pair what determines the quality of the cable
number of twists per unit length
Twister Pair – Transmission Characteristics
- needs amplifiers every 5-6km (analog)
- needs repeater every 2-3km (digital)
- digital or analog signals
- limited distance
- limited bandwidth (1 MHz)
- limited data rate (100 MHz)
Types of twisted pair
- unshielded
- shielded
Characteristics of unshielded twisted pair
- ordinary telephone wire
- cheap
- easy to install
- suffers from EM interference
Characteristics of shielded twisted pair
- metal braid or sheathing
- expensive
- hard to handle
Propagation method of unguided media
- Ground propagation (below 2 MHz)
- Sky propagation (2-30 MHz)
- Line of sight (above 30 MHz)
Unguided media/Wireless transmission waves
- Radio wave
- Microwave
- Infrared
- Typically range from 3 kHz to 300 GHz, covering various bands like AM, FM, TV, and mobile communication.
- Travel through free space and can penetrate walls, making them suitable for both indoor and outdoor communication.
Radio waves
are a type of electromagnetic wave with frequencies ranging from 1 GHz to 300 GHz, used extensively in communication systems due to their high frequency and capacity for carrying data over long distances.
Microwaved
uses electromagnetic waves with wavelengths longer than visible light but shorter than microwaves. Are commonly used for short-range, line-of-sight communication. Falls in the range of 300 GHz to 400 THz (wavelength: 700 nm to 1 mm).
Infrared
are devices used to transmit or receive electromagnetic waves, converting electrical signals into radio waves (and vice versa). They play a critical role in wireless communication, enabling signal propagation over the air.
Antennas
Types of satellite link
- Satellite point to point link
- Satellite Broadcast link
Characteristic of line of sight transmission
- Free space loss
- loss of signal with distance
- Atmospheric Absorption
- from water vapour and oxygen absorption
- Multipath
- multiple interfering signals from reflections refraction
- bending signal away from receiver
