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O'Reilly's Antenna Shootout
nickynicky9doors writes: "From Rob Flickenger O'Reilly Network's Systems Administrator :
'Gregory Rehm hosted an Antenna Battle Royale between a Lucent popsicle stick, a couple of Pringles Cans, our Coffee Can, a Hunt's Tomato Sauce can, and a 40oz can of 'Big Chunk' beef stew. Who was the winner?'" Let's just say it doesn't come loaded with saddle-shaped styro-chips.
If you're doing no better than omni, you may have an impedance mismatch to overcome. Pattern might be just fine.
But hey, it's a quarter wavelength. I guess anything's possible. If you'll excuse me I'll go and attach an N connector to that birdcage now.
icqqm [ICQ:11952102]
yes you have to boot both sides to get maximum range, but these are directional.. so you have to have your laptop in aspecific location and never ever move it. Or, use it as a point to point link like the other 98.765% do.
Basically, if people quit trying voo-doo antenna designs and buy a ARRL handbook and learn a bit about what they are doing they would get a 95% sucess rate. antenna is the least of problems..
here's what you need to do. If your wireless card isnt within 5 feet of the antenna you have to buy super expensive $22.95 a foot hardline and $80.00 connectors for each end. Moral of the story? put your couputer acting like your end of the link in the attic within 5 feet of the antenna, and use Belden 9913 and N connectors. anything else is just a waste of time and power. (RG58 has a 25db loss per 100 foot at 2.5ghz that is 2.5db per foot or you lose 50% of your signal every foot of RG58 wire... so those that use it are wasting their time.) impedance mismatches cause huge problems at 2.5ghz your soup can is NOT a 52Ohm load unless you have everything perfect as to the stub length, position in the can. and position from the back wall of the can. it's easier to modify a old KU band sattelite feedhorn than make a working soupcan. your impedance bump will cause about 2-4DB of loss... another 50% of your signal gone.. (that's both transmit and recieve folks!)
Now, use a nice old primestar dish? Awesome linking.. they are great and deliver approx 30-50DB gain... the best is to use 7foot spun aluminum dishes... but the neighbors whine about those.. (but you get 100-140Db gain)
There;s a reason other than greed as to why the professional antennas are pricey.. do some reasearch and get good at aluminum machineing by hand and you can make commercial quality stuff.
Do not look at laser with remaining good eye.
The point of building this particular antenna was to create a unidirectional unit for building point-to-point wireless networks. Making it unidirectional also cuts down on the noise.
the lucent popsicle is nothing more than a 5/8ths wave antenna.. signals not at the horizon will suffer (up.down)
The pringles can is nothing more than a basic beam.. 1 driven element and 1 reflector (the metal bottom) it is not acting like a waveguide because the "metallic substance" is not electrically conductive (in my tests... if people in other parts of the country would test theirs? it would be interesting.)
The metal cans are a type of waveguide... more of a feedhorn design.. they would be awesome pointing at the focal of a dish. if you were to put a 45Deg cone around the opening you would further increase the gain of the can.
The best thing to do is modify a existing 2.4ghz feedhorn or antenna. you'll find them on Primestar dishes and KU band old sattelite dishes. they need a bit of tweaking (filing on the stub) but work best and the little aluminum concentrator on the old sattelite dish types ( the set of concentric rings around the feedhorn opening) will give another 2-3db not in gain but in selectivity and rejection of off axis signals. (better noise floor)
Do not look at laser with remaining good eye.
You might try this guy out - its mainly build for AO-40 work in the 2.4 ghz range - should work really well for you 802.11 distance freaks :).
http://www.n3iyr.com/
Second, people have done the Primestar dish thing before and report 22db gain with it, not 30-50.
Third, according to the ARRL antenna handbook, the 200" optical receiving antenna known as "Mt. Palomar" has 148db gain. Frankly, I don't think anyone's satellite dish compares to this (or could, at microwave frequencies)
Remember, 100db gain means 10 million watts of effective radiated power for every milliwatt of input power.
Antennas with over 30db of gain simply are not that common.
Serious answer: http://www.borg.com/~warrend/guru.html
These things perform miserably, for a much better design, have a look at:
http://users.bigpond.net.au/jhecker/
For a 2.4GHz hellical that is simple to build, these things are great.
This page gives actually useful measurements and a great bulding guide. I would (and do) use one of these over these non-functioning cans any day.
In the article, he describes having to point the antenna to one side of the target. This sounds rather like the antenna dimensions were wrong. In a yagi array, the main lobe will be to the front, with minor lobes coming off at various angles. The same should be true of any antenna (directional) either waveguide or dish. I couldn't see where he'd allowed for 'velocity factor' in any material length calculations. Also, when constructing a half wave di-pole radiating element, the capcitance across the antenna will cause actual dimensions to be shorter than theoretical. Driven element spacing also affects the shape of the pattern. It can be that a lower overall gain acheives better results than by having a better radiated pattern, the pattern can be affected by driven element position etc. Its a very technical subject, its worthwhile looking at the 'VHF & UHF Handbook' for more information. Still, a very interesting article combining two of my interests!
Merlin --- We're an autonomous collective... Help, Help, I'm being oppressed!!
A waveguide antenna feeding into a dish reflector is called a feedhorn. They work very well.
The truth shall set you free!
the 'regulations' define the allowable total output power, the amount of 'focusing' you do is not controlled, since this does not ever actually increase the total output power.
the 'soup can' is a very crappy setup, it lowers the total ouput power a LOT (due to impedance mismatches) and gains a little by focusing this lower power reasonably. the helical actually has an impedance transformer, so uses all the power you have, a much better setup.
may I sugest you read up a little on radio transmission, and all will become clear.
You can find other 802.11b antenna experiments in Finland and in Belgium with HomeMade antennas (this is in french, sorry). The 'KoekelBerg2 experiments' show the signal strength for a 3.9 km link with home made helicals and tin cans. We also got -85/-98 dBm with a can on a side and a simple lambda/4 wire on the other (the measure is on this side). We don't know if the apparent better performance of tin cans over helical antennas (which are much more difficult to build) is due to some error in our helical design (based on Jason Hecker's design) or not. I've got some other links here And, just a note about dB's : adding 6 dB allows you to double the distance.
No such thing as a Yogi.....you mean yagi. The link you have on your post is talking about STACKED Yagi's. By stacked, I mean they take 2 or more yagis and mount them on a boom with the elements paralell to each other and then have a different wiring. A piece of coax comes from each antenna and meets to form one piece of coax that's fed back to the radio. This has a way of increasing your directional gain alot. This is why this config is used for EME work on 2 M woith a 100 wat all mode 2 M rig. It can also be used for satellites.
You may be takling about a log periodic antenna where all elements are the same length, but are connected much differently together.
The O'rielly article is pretty amatuerish for even an amatuer. He stated that a Yagi is hard to build. Yagis are not hard to build, you just have to know what your doing. I can build a yagi for 2m cheap with a good metal hanger. Yagi's for 2.4 GHz are different, but they are doable, even by an amatuer antenna maker. That ARRL antenna book he bought is a good book and it can teach him how to build an antenna that he likes.
If you are just looking at increasing the omni directional range of your 802.11 card, these antennas won't do you any good. They concentrate the signal in a certain direction. They could be used successfully in linking (bridging) parts of a community wide 802.11 network, but where there would be a concentration of people, you would want an omni directional antenna on the AP. a 5/8 wave antenna would be good, but maybe they should look at a full wavelength aerial. At the frequency, it should not be that long (consider that CB'ers use a full wave all of the time on their pick-ups and tractors....).
Gorkman
What I find interesting about the shootout is the fact that while the antenna design is definitely not exactly what you call optimum, this is truly homebrew electronics design at its best.
I'm sure anyone who's read the ARRL handbooks on antenna design will come up with a slightly more expensive, but still home-built design that will substantially outperform the food can antennas. Indeed, one other poster mentioned a homebuilt antenna built in Australia that really worked well for 802.11b wireless networking using PVC tubing.
Here's an old article, where a fellow achieved 14km in testing (not just signal strength, but actual data flowing).
Also reports of 57km achieved by Lucent engineers, staying within FCC specs.
-me
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