 |
 |
 |
 |
 |
|||
 |
 |
||
|
|
|||||||||
|
Wireless AntennasThis web site is hosted FREE by Servin Mervin
The single most important part of setting up wireless links is the antenna system. It is by appropriate placement and use of antennas that the range of a wireless network can be extended. There are all manner of possible antenna combinations, depending on the installation, but if you follow a few basic rules, your installations will work fine. Omnidirectional AntennasOmnidirectional antennas are perhaps the least useful antenna for WiFi. At the power levels that we work with, radiating it through 360 degrees just doesn't work very well. Because you are radiating through 360 degrees you are also receiving throughout 360 degrees and therefore more succeptible to interferance as well. For each of our Access Points, to achieve omnidirectional radiation, we use two slotted wave guides back to back. There is always a situation where an omni is just fine, but generally for uses less than a couple of hundred meters.Directional AntennasThere are many different types of directional antennas, each having properties that may be desirable for different installations. You will need to use two directional antennas pointing at each other for links over 300 meters. Longer links require antennas with higher gain. As antenna gain gets higher, so does the size of the antenna, and the price of the antenna, and it's difficulty of use. This is why you wouldn't want to over-kill every installation with the best dish antenna you can lay your hands on!! Below is a general guide for LOS links that we work to. 300M Omni to Omni 300M - 1Km Cantenna to hi gain Omni, better still Cantenna to Cantenna 1Km - 4Km Vagi to slotted Waveguide, or better still Vagi to Vagi 4KM - 6Km Dish to Vagi, or better still Dish to Dish 6Km + Dish to Dish with good LOSPolarisationSince most noise is vertically polarised, in order to add a couple of Db of noise attenuation, use verticle polarisation.Coax RunsThis is simple - keep em short. At WiFi frequencies, coax is lossy and expensive. It's therefore cheaper and a LOT more effective to mount your AP in a waterproof enclosure near the antenna and run UTP with POE to the Access Point |
