I have been asked “what is WiFi” by several people after I tell them what I do so I thought I would put my standard answer into a post for others who may be thinking the same thing.

Wikipedia also has an entry on the what is WiFi question.

WiFi is basically a term for the set of guidelines which allow interoperability among various wireless networking products from different manufacturers. This set of standards has allowed the use of wireless networks to explode in recent years.

Back in the mid 90’s before the official 802.11 standard was ratified, a friend of mine introduced me to some 900 Mhz DSSS (direct sequence spread spectrum) radios. These radios provided a wireless serial link between computers. They cost around $AU400 a pair back then but they were extremely useful devices

Infowave wireless modem

Out of the box, these units allowed a connection of a few hundred feet or so, but once modified to accept external directional antenna’s we achieved links over 7km. To me this was a very exciting achievement and led to many adventures linking low cost wireless devices using many different antenna combinations.

Of course once the WiFi standard was adopted, prices plummeted. I still remember paying $US600 each for my first few pre-802.11 PCMCIA wireless devices which I had to import directly from the US. These devices didn’t come with an external antenna connector so once they arrived, they were quickly dissected and modified.

The longest link I have personally installed was 38km, over Port Philip Bay. We were using the old trusty Linksys WAP11’s (same functionally as Dlink DWL-900AP) flashed with Dlink firmware and Hills 25dB parabolic grid antennas. The link was a little sketchy with a lot of duplicate packets (I assume from the reflections off the water) but it worked!

Linksys WAP11

Hills 25dB grid antenna

These days the equipment is much better and devices can be found with very good receive sensitivity. This is very important in establishing links greater than a few km’s.

So in a nutshell, WiFi devices are very cheap now with some having very good receive sensitivity. Good antenna’s can also be found at similarly low prices, so what are you waiting for?

Here is a list if what you will need to set up your own long range WiFi link.

• wireless device with external antenna connector (RP-SMA)
• pigtail adapter (RP-SMA to N type)
• low loss antenna cable (N type to N type)
• directional antenna (N type)

Please let me know how you go.

Categories: Wireless

When your setting up a wireless network for maximum range, the wifi antenna cable becomes very important. This is because most of the time your access point or other wireless device will be located inside the building but the antenna must be mounted outside where it is providing maximum coverage and free from obstructions.

A good way is to set up your equipment up as close to where your antenna will be mounted as possible. In some cases it is preferable to mount the device in a weatherproof enclosure with the antenna or in the ceiling space just below the antenna. This configuration is optimal as it minimizes cable losses.

Where your cable length can be kept at reasonable length (around 10m/30ft or less for LMR-400), it may be easier to run a low loss coaxial cable. These cables generally have an ‘N connector at each end. You will just need to make sure of the gender of the N connector on your antenna and the N connector on your pigtail to select a suitable cable. Most wireless devices have a very small connector and a pigtail is required to convert from this connector to an N type.

pigtail adapter to connect your wireless device to the N connector on your antenna cable

Low loss antenna cable with N type connectors

It is important to keep the antenna cable as short as possible even when using very high grade cable. As you can see from the chart below, the 2.4GHz frequency degrades a lot more than lower frequencies along the cable length.

Categories: Wireless

This short YouTube video shows you how to make an inexpensive wifi extender for your access point or router. You need to print out a template and construct a small parabolic reflector. Very simple and cheap idea that works!

Categories: Wireless

Wireless or Wifi antenna’s are separated into two main types, directional and omnidirectional. For long distance work there is no substitute for a good directional antenna. While focusing the transmitted signal to cover greater distance, the receive performance is also greatly enhanced. By listening in one direction only, a significant amount of ‘noise’ from other directions is eliminated, providing a better ‘signal to noise ratio‘.

The performance of an antenna is measured in dB. For every 3db of gain the power is doubled. Most manufactures specify gain as dBi (dB gain over an isotropic or fictitious antenna radiating equally in all directions).

When using an antenna to increase the range of your wireless network, be careful not to violate any local laws governing output power. Because the signal is magnified in one direction the EIRP (Equivalent Isotropically radiated Power) is increased.

The Australian legislation covering ouput power is here.

Basically in Australia 2400 to 2463Mhz (channels 1-9) maximum EIRP of 4W (36dBm) and 2463 to 2483Mhz (channels 9-13) maximum EIRP of 200mW (23dBm).

As you can see, this grid or parabolic directional antenna is designed to reflect the signal into a focal point. This is similar to how a magnifying glass works with light. This type of antenna usually provides the best gain and thus the longest link distance. It can focus the signal into a very fine point.

Another type of directional antenna is a yagi. The bigger elements on this type of antenna also serve to reflect signal back to the main element, thus focusing the signal from one direction.

Even though omnidirectional antennas do radiate in all directions, they too can be made to perform better by improving their gain. In this case the sphere pattern that would surround an antenna with no gain, is squashed flatter to provide better coverage out to the sides instead of wasting energy transmitting up and down.

Obviously with all antennas, the improved gain performance also works for the received signal.

Categories: Wireless

One of the biggest drawbacks of using wifi is that wireless range is usually limited to about 100 metres or less. I guess this is a lot better than being tethered to a cable but now that we have a little mobility, we want more!

The 2.4Ghz frequency that a typical wireless network uses does not like going through objects as much as lower frequencies do. So things like walls and other obstacles quickly dissipitate the signal.

You can greatly improve the range of a signal by using an external antenna. Most laptops these days come with internal wireless cards which have the antenna routed around the LCD screen. So unless you want to make hardware modifications, or fiddle inside your laptop, rules out using an external antenna.

The answer is to use a USB wireless device. Choose one that has an external antenna connector which will give us the ability to really improve the range. Even the supplied ‘rubber duckie’ type antenna included with these devices is a great improvement over the standard internal PCB type antenna.

I picked up a cheap device on eBay a few weeks ago for under AU$25.00 delivered to my door. I don’t know they do it and it makes me relieved I got out of the wireless hardware business!

(Please excuse the pics as they are taken with my MacBook and SE K800i Phone)

This device comes with Windows and supposedly MAC drivers but I used ZyDAs drivers on my MacBook which seemed to do the trick. The range with it plugged in is a lot better than with the internal MacBook airport card but the real advantages will only be seen once we plug an external antenna into the RP-SMA connector on the USB stick.

OK, now the part that makes all the difference. We need to use a pigtail. This is a short cable that plugs into the RP-SMA port on the USB stick and converts it to a standard N type connector. The N connector is what is used on most ‘real’ antenna’s due to it’s low-loss characteristics.

Now we have a standard N male connector which we can connect to a small directional panel antenna. As soon as you use a directional antenna you will notice huge improvements in range, This is because you’re doing away with a lot of noise coming from the other directions you are no longer receiving. So the more directional the antenna the better the range (providing you have the antenna aligned).

Now we are all set, you will see huge gains in signal strength which will provide far better coverage than the internal type antenna found on most laptops.

Categories: Wireless