April 2004 Archives

     While doing a lot of work on the new Darien-Wifi project, I have also spent a lot of time testing different OS's on the desktop. While extremely happy with OS X - and more so when I wander away and come back - I am still inclined to try different interfaces out of sheer curiosity. Since 1998, I have tried to install and use SuSe at least twice a year. Although happy with much of the RedHat ease of installation (and the fact that they had always offered ISO's for the CD set free to download - which SuSe does not), I always disliked the increasing similarities between Microsoft's OS products and RedHat's distribution of Linux. Too often, the subscription element of RedHat reminded me of the Microsoft update procedure. Although I am here to say that every mainstream and semi-mainstream OS has some sort of update service (OS X's can become as irritating as Window's) that will become annoying at one point or another, I simply don't care for Microsoft's nor RedHat's. Plus, RedHat eventually announced that they were dropping desktop support and going to focus on providing server distros. This year, I am on my third install of SuSe and am impressed. The standard KDE interface is pleasant and it is fairly responsive on everything from my PIII SpeedStep Sony Vaio SRX99 to a P 4 2.5 Ghz Compaq/HP desktop. I wouldn't dare try it on an older PII machine (I can't imagine the gui would be very responsive), although there may be tweaks out there to overcome some of the issues one would have with a slower machine. There are many aspects of power management that I haven't taken the time to get working on the Vaio, but SuSe does work. YaST takes a bit of getting used to, but it has been more intuitive for me to use than RedHat's install tool and package manager. This is not to say one is necessarily better than the other – the install process and application installation process on OS X is by far the easiest and most intuitive for those just starting out on a computer – I think YaST does a better job of telling you what you have installed and what you have for options. On top of that, YaST helps manage many other configuration items on your machine. Now that I have been using it for a while on a desktop (with a big screen), I see how I might have better dealt with problems I had on the Vaio. If you simply want to use your computer for web browsing, emails and word processing, there is no reason why I wouldn't recommend you try it.
     Although I find SuSe very praiseworthy, I would caution those who are not power users who like to tinker a lot. Get a Windows or Mac machine. With Windows your biggest trade-off is security holes and virus threats. But, as with any machine, if you maintain what you have and are careful, you can go through life without virus and security run-ins. If you want a machine that is simple to use, is unlikely to be a virus or security threat target and allows for quite a bit of modification, go with a Mac. SuSe is something I would feel comfortable setting up for my parents behind a hardware firewall/router. I would sleep at night knowing it is unlikely they would inadvertently infect their computer with a virus. It would also give me peace of mind regarding stability. How often does your Linux or Mac crash? Outside of those who really like to muck with the interface and install all kinds of apps that modify the gui and underlying system, it is a rare occurrence for those [Mac and Linux] users who really use our machines as tools. For those of you who are power users, I have heard complaints that SuSe locks you into their way of doing things. I don't know how to respond. The one delightful item that I found while installing the system (on the computer I am using to type this) is that I had a choice between Apache 1.x and 2.x. I lamented over the Apache 2.x issue some time ago with RedHat and was happy to see that I had a choice this time around. I still won't put Apache 2.x on any of my production machines – and I don't know many who would.
     Between the good looks of the interface and the ease at which I was able to accomplish all that I needed (so far), I am impressed. My 2 cents...

[BAWUG] dBM and dBi
Tim Pozar pozar@lns.com
Thu Mar 7 15:39:00 2002

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On Thu, Mar 07, 2002 at 06:06:59PM -0500, Stefan Schueller wrote:
> How do I convert dBM to dBi or watt and what is the legal limit? 36dBi or
> dBM?

Both answers can be found from my paper "Demystifying the FCC's
Part 15 Rules and Regulations on ISM power limits" at:

http://www.lns.com/papers/part15/

--
At the end of the paper...
--

1.deciBels - dB

dB, or one tenth of a Bel, is a unit of mesurment that looks
at the ratio of one value to another. Gain or loss can be
measured in dB. The dB scale is an exponential scale using
the formula log(ratio)*10. This means that 3 dB is about
twice the power, 10 dB is 10 times the power, 13 dB is about
20 times the power and 20 dB is 100 times the power.

2.dBm

dBm is deciBels referenced to a value of 1 miliWatt of
power. Power over or under 1mW would be plus or minus dBm
respectively. If you have a transmitter that produces 1
watt of power that would be 1000 times more than 1 mW so
that converts to 30 dBm.

3.dBW

dBW is deciBels referenced to a value of 1 Watt of power.
Power over or under 1 Watt would be plus or minus dBW
respectively.

4.Effective Isotropic Radiated Power - EIRP

Effective Isotropic Radiated Power defines the gain of an
antenna over an "isotropic antenna" that would radiate
equally in all directions.

If you have an antenna that radiates better in one direction
than another, it would have gain in this direction. The
amount of gain would be shown as "dBi" or dB gain (or loss)
over an "isotropic antenna".

--
Snail: Tim Pozar / LNS / 1978 45th Ave / San Francisco CA 94116 / USA
POTS: +1 415 665 3790 Radio: KC6GNJ / KAE6247
"It's a damn poor mind that can only think of one way to spell a word."
- Andrew Jackson
"What is wanted is not the will to believe, but the will to find out,
which is the exact opposite." - Bertrand Russell, "Skeptical_Essays"

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     I have been racking my brain trying to figure out how to install the terminal app for the Zaurus. I found the correct URL for the program, put it into the address bar of the older version of Opera that was on the device and tried to download it. I tried as I might but couldn't figure out how to. It kept downloading the ipkg package to the /temp directory. The installer (Add and Remove Software) package could not find the file I just downloaded... and thus I went 'round and 'round. I finally looked up the manual for the Zaurus at Sharp USA (the How to Install Software and promptly saw that you cannot simply load software from the device - you must load it via a removable memory card (SD or CF) or via the sync software. The ironic and most irritating bit about the Zaurus is that it only syncs correctly with Windows. (Those of you who do not understand the inherent irony: the Zaurus is a Linux device... and there is no pre-packaged sync software for Linux... for a Linux device. Crazy!) Luckily, from my last go-around with the Zaurus, I had all of the necessary packages on a CF card in my brief-case. I popped the CF card into the device and started up the install program again. At that point, I was able to see all of the packages I had gathered up until now on the CF card and installed the necessary apps: ssh and terminal. I still am amazed at how difficult the device is to use with other Linux devices. I like it, but I don't like it all the time. Lesson learned: keep a spare CF card around for installing software on the Zaurus. You'll be thankful you did.

Start with SuSe an install CD downloaded from one of the SuSe mirrors. (I still haven't tried nor figured out how to download the complete collection - which is helpful timing-wise when installing the system afresh.)
Boot install CD.
Activate kernel module for the Intel PRO/100 network interface.
Install via FTP using the beginning instructions from Tutorial: How to install SuSE 9.0 via ftp. Essentially, the trick is making sure to use a viable mirror for the sys-install. In the case of the howto I am referencing, the writer uses:

It is a good idea to test different mirrors and see how many hops they are away from your location. I have done extensive FreeBSD installations and have found two mirrors to be relatively close to me. Ironically, the mirror that is theoretically up the road from me at University of Wisconsin - Madison is at least 3-5 router hops farther away than a mirror through Pair.com's service. (Another lesson that net transfer efficiency is related to the logical and not necessarily the physical organization.)
After downloading the latest YAST program, YAST started and I made the appropriate selections. Because I didn't have anything on the Windows partition to worry about, I took the chance and allowed YAST to automatically partition the hard drive. After all selections of desired configurations and programs were made, I let YAST go to work and download the needed files from the gov's mirror (finally, my tax dollars at work for me).

     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...