Tony’s Cafe

I’ve been putting together plans to get G-NET2 working — a wireless data link between my house and my friend’s house 6-7 miles away. I tried a few different antenna designs to work with WaveLAN cards and no luck yet! Each antenna design was a learning experience — after making each antenna, I’d review what I did wrong and try to make a better antenna. Now I think I’ve come up with a good antenna design but to test it, I decided to use a phone (voice) mode instead of data. If I test the antenna with two 900MHz radios, I can at least hear Doug on the other end and see if he’s coming in strong… or not at all.

I did some research on (of course) cheap 900MHz radios. Now that I’ve had my ham license for a year, I’ve learned lots of good stuff about radios and antennas. I learned that a cheap way to get on 900MHz phone is to convert a commercial 900MHz radio. Most commercial 900MHz radios transmit over 1 Watt, the unlicensed limit. Since I have my ham license, that is not a problem! I settled on the E.F. Johnson 86xx series mobile radio. Here’s what I did…

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I miss the days of Citizens Band (CB) radio — back in the 1970s and 1980s, the “Golden Age of CB” — where everyone seemed to have a CB. I guess CB could be compared to a cross between Internet Relay Chat (IRC) and push-to-talk (PTT) cell phones today. There is something else, though, that CBing always afforded. You can chat while driving. If anything could bring strangers together to “shoot the breeze”, talk about common interests, or find out what lies ahead on the road, CB is it. It’s free to use and the one-time equipment cost is less than a one year cell phone plan. The problem is, where is it today?

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In a previous post, I discussed the work Doug and I did, attempting to build some cheap 915MHz yagi antennas. Based on our tests, I was able to design a more accurate 915MHz yagi. Instead of using PVC tubing for the boom, I changed the material to a 3.8cm x 1.9cm (1.5″ x 0.75″) wood boom. The wood boom was far more easier for drilling accurate holes for the elements. This yagi was relatively easy to make; the materials for two antennas were less than US$10. In a quick test using Aironet Arlan 915MHz access points (with one of them in repeater mode,) we were able to go 250m through a forest. In this post, I discuss how to make these directional antennas and how we tested them.

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If you are experimenting with 900MHz wireless, 915MHz WaveLAN cards can be a cheap way to set up a point to point link. You can usually find these ISA cards on eBay and are supported by most Linux kernels. If configured properly, they can be set up for IP routing to create a gateway for a point to point link. (I won’t get into the Linux drivers and routing here, only testing a link with the WaveLAN DOS utilities.)

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In a previous post, I discussed the possibility of linking my house’s network to my buddy Doug’s house, 6.5 miles (~10.5km) away. Using 2.4GHz technology with 200mW and 14dB yagi antenna’s didn’t do the trick. I wondered, though… could I utilize wireless networking in the 900MHz range? 900MHz can definitely go through trees and what not a lot better than 2.4GHz. I heard about a ship-to-shore link that used both 2.4GHz and 900MHz wireless networking technologies… once the 2.4GHz signal disappeared, the 900MHz network link would kick in and give the ship some extra distance. (Of course, though, that was over open water! I need to go through trees, houses, and bounce off rocks.) O’Reilly’s Wireless Hacks book states, “As the frequency of a signal increases, the apparent range it can cover at the same power and gain decreases. For example, a 100mW signal at 5.8 GHz appears to travel less than half the distance of a 100mW signal at 2.4 GHz, which appears to travel less than half that of a 100mW signal at 900 MHz.” (Wireless Hacks, Hack #7). I also read a post on Broadband Reports where someone was able to shoot a 900MHz link 9.7 miles through thick pine trees.

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…through 6.5 miles (~10.5km) devoid of “line of sight” landscape, that is! Doug and I are trying to get a wireless link up between our houses. Six years ago, before the days of DSL and when we had apartments near each other, we had a wireless link. Using 915MHz WaveLAN cards and Linux, we were able to link up and play Quake against each other. Back then, our apartments were only a couple hundred feet away from each other, and we utilized some low sensitivity patch antennas. As long as we aligned the antennas out our windows just right, we could establish a connection. Now, we’re 8 miles away from each other, and we’re wondering if we can do the same thing.

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I’ve been meaning to put up information regarding my experiences with 2.4GHz 802.11, amplifiers, and antennas. I have designed and implemented some installations for ship-to-shore use, to provide high speed TCP/IP communication to the Internet. There are some radio power restrictions to be aware of and ways to calculate the power output of a 2.4GHz system. Also, there are different places where you can purchase this equipment, to help keep down on the cost… which is always a factor.

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This is a paper that I presented at the Northeastern Educational Research Association Conference (NERA) in 2003. It describes the use of 802.11b wireless networking technology to support broadcasting live video from a research vessel at sea. This paper discusses how this technology was utilized for supporting learning in the Classroom of the Sea Project. The overarching goal of the Classroom of the Sea Project (COS) is to enhance scientific literacy and provide greater opportunities for deaf students by developing and testing the effectiveness of an authentic learning environment and problem-based learning to teach science to deaf students, and to demonstrate the features of the model to others so that they may adopt them under different authentic learning contexts (Babb, Brown, & Schifele, 2001).

Download the paper Wireless Networking and the Classroom of the Sea [148KB] (Adobe PDF).

Somewhere in my basement, collecting dust, is the good ol’ trusty 900MHz ISA WaveLAN card that would link me up to Doug’s apartment pre-DSL-days. Doug ‘aquired’ a NCR WaveLAN card with two antennas, and I was able to get a WaveLAN card on eBay. We hooked these guys into our Linux routers, hung some panel antennas out our apartment windows, and established a nice 1-2Mbs link for Quake! (Of course, we spent a few minutes trying to line up the antennas just right as our apartments were about 200 feet apart and didn’t quite face each other.) We were in complete Geekdom! Our network name: WGNET. (Wireless Grange Network… another story for another post…)

Hopefully someday we can establish the link again, or I can find some usefulness for this awesome card. I did find a great page for building antennas and amplifiers for this card! Hacking the Original 915MHz WaveLAN from the Low Cost Wireless Network How-To page.

I’ve also posted some information on designing and building your own 915MHz yagi antenna for less than US$10.