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’ve been told I should write some “less tech, more anecdotal” posts. (Mostly by friends who are tired of reading posts like how to build a Commodore 64 RS-232 interface.) OK. So, in that particular post, I referred to a null modem network I designed called G-NET. G-NET was the answer to our frustrations with data connectivity in our dorm, Grange Hall at UConn, in 1992. In 1989, data jacks were installed in all the dorms on campus. Most of them, like the ones in Grange, were not active. (As a side note, the Grange data jacks didn’t become active until sometime around 2000. 8 years too late! Although, had I decided that being an undergrad was a career…) These inactive data jacks taunted us by saying, “Play Modem Wars with your 2400 baud modem, fool!” We wanted something more; something high speed… something in the 38400 bps range. (That’s 0.038Mbps up/down for you broadband compares.) I figured I could probably make some kind of serial null modem network, at least between two nodes. Something that could run over telephone wire. Something with an intercom. Ah yes, I would create… G-NET. What follows is the story of G-NET, schematics, and photos of the Grange Hall dwellers that participated. (The following photos were taken with an Apple QuickTake 100 back in December of 1992.)

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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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