steven n fettig's Jitterin' Thoughts

     In the continuing saga of building out the Darien WiFi project, I have spent the past two weeks learning a very, very important lesson. 802.11b (aka 2.4-2.5 GHz ISM band communications) does not like trees. While surveying for good antenna locations on some of the end-nodes, I did not do anything to take into account natural foliage. We erected the center-node almost 3 weeks ago and at that time, most of the trees were completely bare. So, when we went around to do signal testing, we were able to visually ignore the fact that a tree obstructed a given site or location at the end-node. Over the past few weeks, however, the weather has gotten warmer and the trees are starting to do their spring dance. I thought that some leaves wouldn't be much of a problem considering the strength of the signal and the distance from the center-node. Unfortunately, I was proven wrong. Over the past two weeks, I have seen the signal degrade 25% a week until this week it went well below acceptable long-term levels - I can't imagine what would have happened to the signal when the trees were in full bloom. With the generous help of a member of the BAWUG mailing list, I have learned quite a few things about signal propagation/attenuation and natural interference. I am thankful that I am running into these problems now and not later. It could have been completely disastrous for a few of the end-nodes, as I had considered trees to be small problems and not big ones. So, this weekend will be used for moving the antenna for a third time on the end-node in question. This time, we will be mounting the antenna to a tripod on the roof. I must say that I hate roofs, but this roof installation will be a necessary evil.
     On top of that small lesson learned, I also found how harmful antenna movement can be to the system in general. The original center-node antenna installation was less than adequate. It consisted of a 1 1/4" OD 10 ft/3 m antenna mast attached to a railing on the top of a silo. Well, I learned how flexible a 10 ft/3 m 1 1/4" mast could be. Movement (depending on the wind conditions) were on the magnitude of 2-8" (5-20 cm)! Considering the wavelength of 2.4GHz being 12 cm, this made reception/transmissions horrible when it was windy. With the continuing generous help of my friend, we went up on the tower on Sunday and replaced the mast with a larger OD mast supported with guy-wires. What a difference! Signal levels on the feed and one of the end-nodes increased by almost 25%. I'm sure that with better aiming of the end-node and feed antennas, we could increase the signal effectiveness even further. We still have to replace the feed antenna mount, but for now, we have seen significant improvements in network performance.
Here are some other short observations:
1) While Proxim's Tsunami gear is great, they would do themselves some good by designing a mobile receiver for signal testing. It is a severe pain to try to work out of the back of my truck and stretch out LMR400 cable in every which direction to see where I can get the best signal. Something that I could plug into my laptop would be helpful, thank you very much...
2) When planning the network build-out, plan, plan, test, plan and test some more. Natural obstructions are just as bad as buildings themselves.
3) When budgeting what you are going to spend, multiply it by 3 unless your time is abundant. Mine isn't and many of the work-arounds that I have had to implement have cost a lot of money.
4) And as my father has always said, do it right the first time...