14 - Understand Wireless Principles Flashcards
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A ___ can be defined as an electromagnetic field that radiates from a sender. This __ propagates to a receiver, which receives its energy. Light is an example of this, as the eye can interpret light and send its energy to the brain, which in turn transforms this light into the impression of colours.
radio wave, wave
Different waves have different sizes, typically expressed in __
metres
Another unit of measurement is __ that expresses how often a wave occurs per second
hertz
Depending on the type of information sent, certain ____ are more efficient than others in the air because they have different properties
wave groups
___ determines how often a signal is seen. A wave is always sent at the speed of light because it is an electromagnetic field. Therefore, the wave takes shorter or longer time to travel once cycle depending on its length
frequency
Cycles per second, so 2 cycles per second is 2hz..
Frequency
A signal that occurs 1 million times per second
megahertz
A signal that occurs 1 billion times per second
gigahertz
___ is defined as the physical distance that the wave covers in one cycle
Wavelength
the size of the cycle pattern of an electromagnetic wave
Wavelength
How is a radio wavelength measured?
metres
___ can be defined as the strength of the signal. In a graphical representation, ___ is seen as the distance between the highest and lowest crests of the cycle.
amplitude
___ also affects the signal because it represents the level of energy that is injected in one cycle. The more energy that is injected in a cycle, the higher the ___
amplitude
Amplification can be __ or __
active, passive
What is active amplication?
When applied power is increased
What is passive amplication?
This is accomplished by focussing the energy is one direction by using an antenna
Amplitude can also be decreased – this decrease is called ___.
attenuation
The attenuation of the signal strength on its way between a sender and receiver
free path loss
As the signal or wave travels away from the AP, it is affected by any ___ that it encounters
obstacles
The word “__” refers to the fact that loss of energy is simply as a result of distance, not obstacle. Using the word __ is important when referring to __ path loss, because ‘path loss’ takes into consideration other sources of loss
free
What causes ____ is not distance itself as there is no physical reason why a signal is weaker farther away from the source
free path loss
___ is a measurement of how well a device can receive the signal. More commonly this is called signal value. __ is usually expressed in decibels to 1 milliwatt (dBm)
Received Signal Strength Indicator (RSSI)
___ is a grade value which can range from 0 (no signal or no reference) to a maximum of 255. Many vendors use a maximum that is lower than 255 (e.g 100 or 60)
RSSI
From this RSSI grade value, an equivalent __ is displayed. Again this depends on the vendor
dBm
__ can be caused by wireless devices such as cordless phones and microwaves. This is measured in decibels from 0 to -120. The ___ level is the amount of interference in your wifi signal, so the lower value, the better. A typical __ would be -95 dB
Noise (noise floor)
__ is the evaluation of signal strength after its been affected by noise
Signal to noise ratio (SNR)
SNR compromises of two values:
- RSSI
* Noise (any signal that interferes with your signal)
To calculate the SNR, subtract the ___ value from the ___. Because both values are usually expressed as negative numbers, the result is a positive number expressed in decibels.
noise, RSSI
