More Wireless Basics
This article explains the types of wireless signal. What makes these signals different? What is the difference between a transmitter and a receiver? What do you call a device that both transmits and receives? Make sure you can name two types of antennas and the reason for choosing each type.
Antennas
Wireless routers have different types of antennas. Some routers will have antennas built in, and sometimes the routers will have a choice of antenna you can attach to the router. There are many specific types of antennas, but three basic types are used most of the time, and will be useful in building a wireless network. The first type of antenna is also the most common - omnidirectional.
Omnidirectional Antennas
An omnidirectional antenna sends a signal out equally in all directions around it.
Using omnidirectional antennas has the benefit of creating connections in any direction. You don't have to do as much planning to connect with multiple neighbors or buildings. If there is enough signal between nodes, they should connect.
The all-direction strength of these antennas comes with the drawback of transmitting a weaker signal. Since the signal is going in all directions, it spreads out and gets weaker with distance very fast. If nodes or clients are far away, they may not connect well.
Also, if there are only nodes or clients in one direction of the router, then the signals going in the opposite direction are wasted:
Directional Antennas
The next type of antenna is known as directional - it sends out a signal in a more focused way. There are two main types of directional antennas:
| Sector Antenna
|
Focused Antenna
|
| Sector antennas send out a pie-shaped wedge of signal - it can be anywhere between 30 degrees and 120 degrees wide. These are often long, rectangular antennas that are separate or integrated in to a router. | A focused antenna sends out a narrow beam of signal - it is normally around 5 to 10 degrees wide, but it can be a little wider as well. These are often dishes or have a mesh bowl reflecting signal behind them. |
Using directional antennas has the benefit of increasing the distance a signal will travel in one direction while reducing it in all other directions. Since the signal is all going one way, the power that would be sent out in all directions with omnidirectional nodes is now focused, increasing the power in that direction.
It can also decrease the interference received at the node. There are fewer signals coming in to the antenna, since the node is only listening to signals from the direction it is pointing. It won't hear signals behind it or to the sides as well or at all. This reduces the signals it needs to sort out, and allows it to focus on other signals more, increasing the quality of those connections.
However, directional antennas also have the drawback of requiring more planning to create links in your neighborhood. Since you are defining and limiting the areas where wireless signals go, you need to think about how those signals cover your neighborhood. If there are areas that are then left out, how will those areas be included in the network?
Also, the node has a very powerful signal in a single direction. If omnidirectional units, or lower power units such as laptops, are connecting to the node, they may not connect properly. The laptop will hear the node very well, but the directional node may not hear the laptop. This will create the situation where it looks like there is a strong signal, but you cannot connect.
Quick Activity: What are the best uses for the different kinds of antennas?
| Antenna Type | Best Uses |
| Omnidirectional Sector Focused |
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What would the best antennas to use for building a neighborhood network?