Jul 222009
 

A wireless USB adapter is a Transceiver:  It is the combined radio transmitter and receiver and hence its name transceiver. Alternative names for the transceiver is simply “radio”. Modern WIFI transceivers tend to be very small. Typically they are half an inch, by 2 inch, by 1/5 of an inch. Because of their small size, they can be packaged into small places: Most modern laptop PC’s contain an internal WIFI radio. Usually it is located somewhere under the keyboard. When there is internal WIFI radio, an external radio can be connected in several ways such that we will describe later.

Note: It is possible to have both an internal radio and an external radio.

 

Two characteristics of the transceiver are important:

 

  1. The power of the transmitter, and
  2. The sensitivity of the receiver.  

The power of the transmitter can be thought of as the loudness with which the radio can “talk” to a WIFI Access Point. A louder voice enables one to have a conversation over a greater distance. Similarly, the sensitivity of the receiver can be thought of as the ability of the radio to “hear” a remote WIFI Access Point.

 

In summary, to maximize distance, we want both a powerful and a very sensitive transceiver.

 

Typical internal transmitters found in laptop PCs or external USB cards have a transmit power in the 100-150mW (milliwatt) range. In comparison, the most powerful external transmitters are 500mW and above. Internal laptop PCs are quite sensitive. Their sensitivity can be in the 80-90dB range, whereas external transceivers have sensitivities as high as 96dB. To interpret these sensitivity numbers, it is important to know that a 3dB increase implies a doubling of distance that can be covered.

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