|Boosting wireless signal|
IntroductionThere are many ways to achieve the success in long range communications. Sometimes a simple technique will boost wireless signal enough or we will need to consider several of them.
Every situation differs from another one, it could be because of budget, because of devices or because of distance. Anyway, it can be done.
Installation of a slotted waveguide antenna outdoors
Wi-FiIndeed, we are talking about Wi-Fi (Wireless Fidelity). There are two options 2.4 GHz (802.11b/g/n) or 5 GHz (802.11a).
Usually 5 GHz are used for outdoors communications between two or more access points (AP), not very often laptops are equipped with 5 GHz wireless cards.
2.4 GHz is the king frequency band, almost every Wi-Fi device uses it.
Note that 2.4 GHz equipment like antennas, or network cards, are not compatible with 5 GHz antennas.
While antenna gain is measured in dBi, wireless power is measured in mW or dBm.
The best is to combine high mW on a wireless card with high dBi on an antenna.
This is the equivalence table for wireless cards or access points.
A standard Wi-Fi router is about 50 mW, a high range access point is about 500 mW, a great USB Wi-Fi card is about 1000 mW, chickens get fried at 3000 mW :-)
This is not the electromagnetic spectrum
Antenna types and polarization
There are mainly two options when choosing an antenna, directional or omnidirectional. While omnidirectional is the standard dipole antenna present in so many routers and access points that looks like a plastic stick, directional ones only send signals on a specific direction with an angle that can be narrower or broader.
Antenna polarizations must be taken into account, omnidirectional antennas have vertical polarization, that means that if we point that little antenna in our router or access point to the sky, then our receiving device must point also to the sky for good communication.
Other powerful antennas
In the standard commercial circuits some antennas are not easily found, we can build and play with them, very powerful when the construction is right.
- Slotted waveguide.
Slotted waveguide antenna
Access point locationThe worst place for an access point would be inside a lead box.
Sites where not to install an access point:
- Inside a cage or similar metal structure like a 19-inch rack.
- Inside any liquid, even rain makes the signal go down.
- Under a table or behind the screen, materials like wood or electronic boards block the signal.
- Behind microwave ovens, big speakers, elevator motor, this kind of devices really block the signal strength.
Sites where to install an access point:
- On a table, with no other electronic devices near.
- On the ceiling, sometimes difficult, but none will block the signal between our AP and the computer, Power Over Ethernet (POE) rules.
- In the middle part of a room, to best cover all the space instead of in a corner.
Antennas that mean to be used outdoors have type N connector (female) and usually we will need a cable adapter, called pigtail, in order to connect it to our access point.
On the access point side the connectors usually are types SMA and TNC.
Note: There are SMA male, SMA female, Reverse Polarity SMA male (RP-SMA male), Reverse Polarity SMA female (RP-SMA female). Letters RP in front of a connector type or the words, Reverse Polarity, denote a male connector with female receptacle or a female connector with male contact pin. This is applied to all connector types.
ObstaclesPhysical barriers, such as brick walls, iron doors, glass and even heavy rain, will affect to wireless signal.
Higher frequencies are more affected that lower ones and the higher the frequency is, faster the data rate will be.
This rule means that when using wireless indoors we will choose 2.4GHz technology because there are brick walls, doors, and 2.4GHz technology could go through them easily than 5GHz. In outdoors communication, where there are no obstacles between two access points, our choice will be 5GHz technology that will be faster.
Walls are obstacles for Wi-Fi, but mainly indoors
POE, USB and cable lengthPower Over Ethernet is a safe technology to pass electrical power and data on Ethernet cabling. It allows us to power up and transmit and receive data on a single cable from our router or switch to the outdoor access point, thus avoiding the dangers of 110v or 220v on the roof.
How long could a POE cable be? About 100 meters (330 feet).
USB Wi-Fi adapters are wireless cards connected to a computer by USB connector, we can use them in a non standard way for outdoor deploying by means of a long USB cable.
The problem is that USB cables are designed for short cables with a maximum length of 5 meters (16 feet). We can extend this by using a 5 meter USB active repeater extension cable (see image below) or joining 5 of them up to a maximum of 25 meters. The use of a self-powered USB hub must be contemplated.
USB long cables will be more expensive than POE technology and must be tested for correct operation before a roof installation because not all USB wireless cards need the same power.
Indeed it can be fun to try.
More data rate implies shorter transmission.
Wi-Fi amplifier, antenna connectors
Wi-Fi repeater, halves the speed