Tämän päivän kysymys- ja vastausistunto tulee meihin SuperUserin hyväksi - Stack Exchangein alaosasto, joka on yhteisöllinen Q & A-sivustojen ryhmittely.
Kuva Karlis Dambransilta (Flickr).
Kysymys
SuperUser-lukija userpal haluaa tietää, onko hänen tarvitsevansa saada korkean vahvistuksen antenneja pitkän kantaman Wi-Fi-yhteyden molemmissa päissä:
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.
Pitääkö käyttäjä todella tarvitsevat korkean vahvistuksen antenneja pitkän kantaman Wi-Fi-yhteyden molemmissa päissä vai ei?
Vastaus
Vastauksin meillä on vastaajille mgjk, Jamie Hanrahan ja David Cary. Ensin ylös, 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.
Jälkeen Jamie Hanrahanin vastaus:
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.
Ja David Caryn lopullinen vastauksemme:
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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