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Boosting wireless signal

Introduction

There 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.

Outdoor slotted waveguide antenna
installation
Installation of a slotted waveguide antenna outdoors

Wi-Fi

Indeed, 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.

Power (dBm)
Power (mW)
Power (dBm) Power (mW)
10 dBm
10 mW
23 dBm 200 mW
11 dBm
13 mW
24 dBm 251 mW
12 dBm
16 mW
25 dBm 316 mW
13 dBm
20 mW 26 dBm 398 mW
14 dBm 25 mW 27 dBm 501 mW
15 dBm 32 mW 28 dBm 631 mW
16 dBm 40 mW 29 dBm 794 mW
17 dBm 50 mW 30 dBm 1000 mW
18 dBm 63 mW 31 dBm 1259 mW
19 dBm 79 mW 32 dBm
1585 mW
20 dBm 100 mW 33 dBm
1995 mW
21 dBm 126 mW 34 dBm
2512 mW
22 dBm 158 mW 35 dBm
3162 mW

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 :-)

No this spectrum
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.

Vertical antenna
one
Vertically oriented antenna
Vertical antenna
two
Antennas always pointing to the sky

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.

- Helical.
- Slotted waveguide.
- Biquad.
- Belgrano.

Slotted waveguide antenna
Slotted waveguide antenna

Access point location

The 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.

Outdoor Access
Point
Good for communications
Access Point in a
cage
Really bad for communications








Antenna connectors

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.

N type connector
N type
RP-SMA connector
RP-SMA type
TNC connector
TNC type


Obstacles

Physical 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.

Obstacles: wall
Walls are obstacles for Wi-Fi, but mainly indoors

POE, USB and cable length

Power 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).

POE, Edgar Allan
Not this Poe
Long cable mess
Cable helps the Wireless, sometimes


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.

USB active repeater
USB active repeater, 5 meters long
USB wireless card
outdoor
USB Wi-Fi adapter for outdoor uses

Data rate

More data rate implies shorter transmission.
Transmitting data on 802.11n at 600Mbit/s will not reach as far as 802.11b at 11Mbit/s.
We have to find the correct balance between speed and distance, or leave it on the auto set option.


Amplifiers and repeaters

Amplifiers are commercially available self powered devices that act as TV amplifiers with our wireless signal. It can deliver 1W, 2W, 4W or more, it depends on the specifications. Drawbacks are their high prices and our country laws about wireless power.
Repeaters are cheaper but we don't like them because every time a signal is repeated, the data rate is reduced to the half. This is because the same radio device must receive and then resend the signal, making it slow.
The repeater mode is not standard, that means it would work only on the same manufacturer equipment and if we are lucky on different ones.

Wi-Fi amplifier
Wi-Fi amplifier, antenna connectors
Wi-Fi repeater
Wi-Fi repeater, halves the speed



World records

Once upon a time there was an unamplified long range wireless world record, even a competition for it.
The world record is about 300 Km, this is accomplished by the use of huge antennas on the highest mountains.

Wi-Fi mini world record
A lot bigger parabolic dish is needed for a world record

We think this is a nonsense competition nowadays but fun as hell.
Defcon hacking conference held in Las Vegas, USA, hosted in the past a contest named "Defcon Wi-Fi Shootout" were several teams tried to achieve the longest link by following the contest rules. There's a digital archive with some pictures of this event.


Low budget hacks

There are software hacks and firmware hacks to give more power to a wireless device than the allowed by the manufacturer, on the other hand hardware hacks look for hardware modification for an extra range.

Some Google images searches to get the idea:

https://www.google.com/search?q=wifi+strainer

https://www.google.com/search?q=windsurfer+wifi

https://www.google.com/search?q=can+antenna

Enjoy by experimenting with easy modifications and get to the hard ones. It is very easy to build our own testing lab.
Power on an standard access point, go far away, connect a wireless adapter to the notebook and connect the antenna, download a large file from your local network and time it. Operating system doesn't matter.



October 2012.

Use main page comments for questions.


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