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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.
They should get together with the Sliiiiiiiiiiiiinky guy. Although there might be issues with reception..."HEY MAN! Quit shaking it!"
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.
might one of these antenas be mounted in reverse, on a small DSS/primestar style dish to improve reception?
just place the end of the pringles can at the focal point of the dish? i would suspect a significant gain from this, but then again the whole point of a pringles can antena is to be cheap, how cheap can a person get a dish?
also, what do you suspect the range to be on one of these homebrew antenas? could it span 2 miles to a passive repeater, then two more miles? or would the repeater have to be and active 802.11b access point?
if i were to hack an 802.11b access point to install a pigtail for a homebrew antena, could i install two pigtails for two antenas? and would it be advisable to further hack the accesspoint to boost the signal to 80-90dB?? i believe the FCC limits these 2.4Ghz signals to 100dB, but dont quote me on that.
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.
yes, the regulations are all about ERP(effective radiated power), not how much power your putting into your feed line. For many services this means that if you are running the maximum power, and add an antenna with more gain, you must drop your power. But for point to point networking in the 2.4ghz ISM(industrial, scientific, medical) band you are are allowed to use directional antenna for point to point communictations, upto i belive 6db gain and still run maximum power. Above that you must drop your power, but the requiered drop is something like 1db less power for every 2db of gain, so it's not to bad. Keep in mind that my numbers are not correct.
But the other thing to consider is that i think most cards dont run the maximum allowed power, so you should be able to use a high gain antenna with any problems.
ALso, keep in mind that the regulation allowing high gain antennas without lower power specifies point to point communications, so that 20db gain yagi ontop of your car might not be legal.
The other thing to remember with 802.11b, is that 802.11b isnt the only thing on the 2.4ghz ism band, and ISM isnt the only thing 2.4ghz is allocated for. There is also amatuer allocation covering the same frequencies, and there has been at least on case of someone having to shutdown an 802.11b network do to interference it was causing. Also always keep in mind
-- free as in swatantryam - not soujanyam.
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/
He makes a big deal about which antenna had the most raw gain. This is only *half* the story. He only makes some vague hint about needing to consider the receiver noise but doesn't consider it like it needs to be considered. Antenna reception is rated in G/T (gain over noise temp). The story talks about G but no one knows what T is. Thus G/T is unknown and his conclusions are somewhat less than useful. A big signal is of no use if it is drowned in a heap of noise.
Yoghurt
That's right, not a yagi but a yogi antenna. It is similar to a yagi (classic unidirectional antenna) but has logarithmic descending elements. In a traditional yagi antenna, all elements in the array are the same size/shape.
I hooked one up to my TiBook via a hacked-together pigtail and lucent/orinoco connector to avoid the weak internal TiBook antenna, and got about 12 dBi out of it, this with no external power. For some yogi antenna info, see: www.ve3gk.com/stacked.htm
http://tinyurl.com/4ny52
That's definitely a phrase I need to use more often.
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.
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!
With the computer in the attic, there is a far better way of doing it, although slightly more expensive. Use an access point (such as LinksysWAP11 / SMC2655W) with power over ethernet, place the AP in a weather proof box, with just the CAT5 connection to it, screw that to your antenna mast (or base if it) and your set. See 1km 802.11b in Egypt for some nice pictures of it.
For cost I guess if your just doing ptp links it is going to cost more, but not that much really, at least here in Australia excluding the cable savings, PoE adaptor, etc, an AP such as the Linksys or SMC can cost less than $450, (mine was $420 cost price) a standard Wireless PCI card will cost at least $300.
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.
These guys are obviously not English majors. From their article (parent linked), one of the cans was filled with "chocolate moose". They must live in the far, far northwest where perhaps one can buy Moose meat coated with chocolate. Doesn't sound as appetizing as chocolate mousse.
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
Love many, trust a few, do harm to none.
On my web site http://www.pythonemproject.com there are some FDTD Python programs that you can use to simulate waveguide antennas. Now these are not GUI based, and there is a learning curve. You basically set up the metal so that its tangential E fields are 0, thats called PEC, perfect electrical conductor. Each bit of metal corresponds to a matrix element. I've been meaning to try out a slotted waveguide antenna on one of my programs, maybe I will get to it and post it there. All of the FDTD programs are GPL, and you can use Animabob to view the E fields in real time.