Archive for the ‘CCNA Wireless Knowledge’ Category

Basic Terminologies

November 6th, 2011 77 comments


An antenna is a device to transmit and/or receive electromagnetic waves. Electromagnetic waves are often referred to as radio waves. Most antennas are resonant devices, which operate efficiently over a relatively narrow frequency band. An antenna must be tuned (matched) to the same frequency band as the radio system to which it is connected otherwise reception and/or transmission will be impaired.

Types of antenna

There are 3 types of antennas used with mobile wireless, omnidirectional, dish and panel antennas.
+ Omnidirectional radiate equally in all directions
+ Dishes are very directional
+ Panels are not as directional as Dishes.


Decibels (dB) are the accepted method of describing a gain or loss relationship in a communication system. If a level is stated in decibels, then it is comparing a current signal level to a previous level or preset standard level. The beauty of dB is they may be added and subtracted. A decibel relationship (for power) is calculated using the following formula:


“A” might be the power applied to the connector on an antenna, the input terminal of an amplifier or one end of a transmission line. “B” might be the power arriving at the opposite end of the transmission line, the amplifier output or the peak power in the main lobe of radiated energy from an antenna. If “A” is larger than “B”, the result will be a positive number or gain. If “A” is smaller than “B”, the result will be a negative number or loss.

You will notice that the “B” is capitalized in dB. This is because it refers to the last name of Alexander Graham Bell.


+ dBi is a measure of the increase in signal (gain) by your antenna compared to the hypothetical isotropic antenna (which uniformly distributes energy in all directions) -> It is a ratio. The greater the dBi value, the higher the gain and the more acute the angle of coverage.

+ dBm is a measure of signal power. It is the the power ratio in decibel (dB) of the measured power referenced to one milliwatt (mW). The “m” stands for “milliwatt”.

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