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La domanda
Il lettore SuperUser userpal vuole sapere se ha bisogno di avere antenne ad alto guadagno su entrambe le estremità della sua connessione Wi-Fi a lungo raggio:
I am trying to understand how long range Wi-Fi works. As far as I know, Wi-Fi consists of Rx and Tx. When a laptop is connected to an AP, the laptop is able to receive data from the AP (Rx) and also transmit data back to the AP (Tx).
Suppose I want to build a long range Wi-Fi setup to cover a large area and I connect a high-gain omni-directional antenna like the one shown in this diagram to the AP.
At 1,000 meters away from the AP and using a normal laptop (without a high-gain antenna), I try to connect to the AP. The signal from the AP is able to reach the laptop, but the signal from the laptop should not be able to reach the AP. Under these conditions, can the laptop actually connect to the AP?
Wi-Fi diagram courtesy of Freeman’s Garage Blog.
In effetti userpal richiede effettivamente antenne ad alto guadagno su entrambe le estremità della sua connessione Wi-Fi a lungo raggio o no?
La risposta
I contributori SuperUser mgjk, Jamie Hanrahan e David Cary hanno la risposta per noi. Per prima cosa, mgjk:
The antenna changes the shape of the transmission. The electrical signal does not become more powerful, but less is wasted during transmission in directions which are not useful (i.e. up and down).
Similarly with reception, the signals are received from a more narrow field, which strengthens reception and reduces interference.
It is similar to talking through a cone, then listening through the cone for a response. The person at the other end does not need any special equipment, but you have increased the range and sensitivity.
Seguito dalla risposta di Jamie Hanrahan:
High-gain antennas provide gain on both transmitting and receiving. So, with such an antenna at only one end, you will get more range than with a standard antenna at each end, but less than with a high gain antenna at both ends.
E la nostra risposta finale di David Cary:
You might also mention antenna reciprocity - if a directional antenna can transmit four times as far as a standard antenna, then the same directional antenna can receive from four times as far away as a standard antenna.
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