7.22.2008

Wireless Antenna Experimentation and Review

I purchased two Gigaware 21-162 wireless antennas from Radio Shack in order to get a longer range wireless connection between two routers. I am going to move into an apartment across the street and from a friend who already pays for internet access and is happy to share it with me. I am going to replace the stock antennas on my 2 Linksys WRT54G routers with the ones from Gigaware in hopes to get a clear signal.

The firmware on the routers I am using are open source router distros that will allow me more control of the transmitters and allow the Linksys WRT54G routers to be put into a bridged mode (which allows for one to connect to the other and bridge two networks into one wirelessly separated logical network ). The master router uses DD-WRT v24 RC6 and the slave one uses Tomato Firmware v1.19.1463

You can relatively easily achieve the router configuration portion of this with these instructions from the DD-WRT Wiki. The Tomato config is just as simple, the GUIs are very intuitive.

The antennas are very easy to install, I unscrewed the factory antennas and screwed the replacements right in. The antennas are twice as long as the factory antennas and give my WRT54Gs a nice ego boost.

The antennas claim to have a 7 dBi gain. I wanted to see what sort of gain I would get after installing them on a router running DD-WRT. I left the advanced wireless settings at their default and got these results:
The results come from running the command: watch "iwlist wlan0 scan" | head on my Debian laptop, which allow me to see a "Quality" measurement and a "Signal Level" measurement. The laptop was about 20 feet from the router and did not move during the tests. Some of the quality measurements would fluctuate by around 4 points, the figures where calculated using an average. (Note that Signal Levels closer to zero are better).

To interpret that data a little bit, installing the antennas gave me a 15% boost if measured by "Signal Levels" and a 12.5% increase if measured in "Quality". In dB the difference was 6 dB, the box claims dBi. (Not sure what the difference is between dB and dBi.

Yes, it would be nice to know how these results affect coverage area...I have not performed any long distance tests yet as that requires my neighbor's to know that I am a complete geek. Don't worry they will come. Additionally, I may add that there are surely some problems with this data - don't quote me on these numbers.

Specifications of the Gigaware 25-162 (from the box):
  • Purchased from: Radio Shack
  • Purchase Price: $7.97
  • Frequency: 2.4 GHz
  • Gain: 7dBi
  • Transmission pattern, 20 degrees vertical
  • VSWR: 2:1 max
  • Impedence: 50 ohms
  • Power handling: 2 watts

I will be moving September 1st and will post the results of the internet sharing attempt.

5 comments:

Colin Gebhart said...

Looks cool,

If you have problems getting a good link between the routers after the move, you should consider switching one of the antennas on each router out with a biquad. They supposedly get about 11dBi and a guy who made one got a good link at 10km.

http://del.icio.us/colinnwn/wireless?page=2

dB is a ratio of 2 power levels, whereas dBi is the ratio between observed power level and that of a perfect point radiation source.

http://www.dslreports.com/faq/14091

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