O'Reilly's Antenna Shootout 149
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.
Pringle Canners Don't Give Up! (Score:2, Informative)
Pringle canning is dying (Score:1)
Re:Pringle canning is dying (Score:1)
Antenna? (Score:4, Funny)
Waveguides? (Score:3, Informative)
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.
Serious question (Score:2)
I mean, if the card in my laptop still sucks can improving the base station really help? Don't you need to improve both sides for a system that sends and receives?
Re:Serious question (Score:1)
Or, as another idea, how about:
Wired network
|
WAP in a bridge setup
|
WAP as the other half of the bridge
|
WAP with a crossover cable or connected via a switch
Now you have a VERY remote connection to your network, all wireless. Need to extend in another direction? Setup another bridge to feed another WAP.
Re:Serious question (Score:3, Informative)
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.
Re:Serious question (Score:2)
That's losing half your power (3 dB) every 12 feet.
--Blair
Your numbers are a bit off (Score:5, Informative)
Second, people have done the Primestar dish thing before [wwc.edu] 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.
Re:Your numbers are a bit off (Score:2)
You mean I could actually get out there with my Radio Shack HT? I don't suppose that I can get that 200" dish on the back of a car...
--Josh
Re:Your numbers are a bit off (Score:1)
Raise your cup to these gents, boys, SALUTE!
Re:Your numbers are a bit off (Score:2)
What he said is:
RG58 has a 25db loss per 100 foot at 2.5ghz
But then he says:
I guess I don't fully grok the exponential scale for decibels wrt loss/foot. I'd think 25db per 100 feet == 0.25db per foot. Care to clarify?
Re:Your numbers are a bit off (Score:3, Interesting)
Yes some have calculated a 22dbi gain from a promestar dish but that is a rarity. It's actually closer to 12-14 in normal attempts with tuning and finer adjustment it creeps toward 20dbi and a 7 foot dsh will give you approx 20-30 dbi with an awesome noise floor and off axis rejection. Arrgh.. I multiplied the dish gain by the feedhorn gain... which giving nice numbers caused some electromagnetic impossibilities.
Re:Your numbers are a bit off (Score:1)
Re:Serious question (Score:3, Interesting)
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.
Re:Serious question (Score:2)
Re:Serious question (Score:2, Informative)
Re:Serious question (Score:2)
Does this really work? I don't know since I don't have a wireless network yet.
I mean, if the card in my laptop still sucks can improving the base station really help? Don't you need to improve both sides for a system that sends and receives?
No. Improving antenna gain, improves both radiated signal strength and also sensitivity to received signals. But of course, doing both ends justice will yield the best results, assuming the antenna designs are appropriate for the task. Having a dish for both ends is overkill and most likely completely ineffective for anything other than fixed point to fixed point comms.
When I get my wireless network gear, I'll be building antennas depending on what I want to do. Half wave verticle for just the home network, but a parabolic dish for links to my local free-to-air geek network. But then, I was working in RADAR in the late 80's and have a few ARRL antenna books since then.
Top notch RADAR systems use little antennas inside VERY highly engineered waveguides pointing to parabolic dishes (for the really high power stuff). If I were these guys, I'd forget the mucking around with this and that, and learn the science to build something that is damn good. There are of course gains to be had with a bit of experimenting, but theres nothing like learning something and then building something which works really well.
BTW, out of interest, the Navy RADAR's are MEGA watt. Eyeball popping at point blank range. If you see a Navy ship in a bay, with it's main RADAR spinning around, it is most likely NOT radiating, they can and do spin at times without any radiating, those BIG dishes can stop in an instant and can also elevate (which is cool to see, since they look like they'd take a while to get up to speed if you did'nt know otherwise). I heard a story years ago about an Aussie ship in a NZ harbor, main RADAR spinning but not radiating... some sailor accidentally switched that bad boy ON....
Re:Navy Dishes (Score:2)
Yeah, I have heard a few times that when au Navy ships in Sydney move out past the heads, into open water, poor unsuspecting seagulls near the ships drop dead into the water when they fire up the main RADAR.
BTW, I was told back then, that our eyes have no natural cooling mechanism (no natural need I guess), which is not good when you get a face full at close range.
Any *current* legal issues? (Score:1)
(And I'm not talking about ISP usage agreements and such.)
Re:Any *current* legal issues? (Score:2)
I don't think you run into legal issues until you start selling them commercially. Then they probably need to be FCC certified, which costs losts of money, etc. Also, there may be some restrictions on maximum signal strength on the ISM bands that 802.11b uses...but that, I'm not sure about, they might just regulate power output.
Re:Any *current* legal issues? (Score:5, Insightful)
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
802.11b Network (Score:1)
DAMN would a 802.11b network be cool to run there... Massive internal gnutella network, here we come!
Re:802.11b Network (Score:1)
Gnutella network? Maybe you should consider using Nutella [nutella.it] jars then!
Re:802.11b Network (Score:1)
Internal bandwidth is not an issue, here (small house, eastnet). I can pull 900K to/from unloaded internal sources.
Conical waveguide (Score:1)
Re:Conical waveguide (Score:2, Informative)
a dish? (Score:3, Interesting)
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.
Re:a dish? (Score:4, Interesting)
Re:a dish? (Score:2, Insightful)
100 dB above what reference? A certain number of dBs of signal doesn't mean anything unless you specify a reference level, like 1 mW or such. Decibel readings are a relative measurement only. They are based on the base-10 logarithm of the ratio of two absolute measurements. I can't imagine that the ratings that you may quote are in dBmW, because 100 dBmW is 10 megawatts!
Re:a dish? (Score:1)
Re:a dish? (Score:1)
Re It's called a feedhorn (Score:3, Informative)
explinations... (Score:5, Informative)
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)
Re:explinations... (Score:3)
> beam.. 1 driven element and 1 reflector
Next time, please actually take a look at the building plans first.
The pringles antenna does not consist alone of the driven element. They are using 5 washers which can probably be seen as director elements. After all its still a weird design, but i think its more of a yagi than of a feed beam.
Re:explinations... (Score:1)
I am not certain that the metallic layer is electrically connected to the back of the can. I don't know if it matters.
A friend and I have made electrical contact between an N chassis connector and the metallic layer. I don't know if this is necessary, but we made contact by putting screws through the screwholes in the N chassis connector and screwing them into threaded flanges with two sharp "teeth" bent out of the flange. (I forget what they're called. My friend found them at a hobby shop.) The teeth pierce the plastic film, the metallic layer, and the cardboard. The metallic layer is connected by the teeth to the flange, by the flange to the screw, and by the screw to the N connector.
Again, I don't know if this electrical contact is even necessary. Every waveguide illustration I see is sort of unclear, but a physics postdoc (friend's brother) tells us we'd best make that connection.
2.4 ghz antennas (Score:4, Informative)
http://www.n3iyr.com/ [n3iyr.com]
Re:2.4 ghz antennas (Score:2)
Of course, you can still use two of the n3iyr antennas, one one each end. Or have the other end use a helical antenna.
Re:2.4 ghz antennas (Score:1)
I wonder what the matchup would be like with most 802.11 equipment? I mean lets face it - from some of these experiments I've read it doesn't sound like anyone really cares about polarity.
Re:2.4 ghz antennas (Score:1)
Re:2.4 ghz antennas (Score:2)
Re:2.4 ghz antennas (Score:3, Informative)
Circular polarization is fine (Score:1)
Questions... (Score:1)
100 watts? On the link listed, that's what they say. But as far as I know, the legal limit to boost a signal in the US is 1 watt. More than that, and someone will hunt you down to shut you down. Right?
It says TRANSMIT, doesn't that mean it's not a bi-directional antenna like you need for 802.11b? Wouldn't something sold over at HyperLink Tech. [hyperlinktech.com] be better, seeing as they are more specifically designed to be used with 802.11b?
Why all the hype on the directional antennas? I would be MUCH more interested in an omnidirectional antenna so some neighbors and I can ALL see each other, not just 1 to 1. Is it just that they are harder to make?
Re:Questions... (Score:1)
Legal limits are all governed by the bands and licenese (or lack there of) they run on.
Omni-directional antennas are more convienant but they offer less gain. If you were to go around your run of the mill omni-directional antenna with a field strength meter you might notice a nice figure 8 pattern - while with a directional antenna you'll notice a considerable amount of the radiation is reflected down what I like to call parasitic elements (elements of the antenna that direct the signal) - the advantage is just distance - you can get a clearer signal into a system with a directional antenna.
Thing is with more amatuer radio sattelites - they are somewhat hard to use with just omni-directional antennas. Take for instance AO-27 - which is a FM sattelite more info here [amsat.org]
With omni directional equipment you'll need a pre-amp - ie something that will amplify the signal coming into your reciever and you'll need at least 25 watts (if not more) going into the uplink. Where with a directional antenna I've actually used this same sattelite with at little as 2.5 watts on the uplink and no pre-amp.
Re:Questions... (Score:1)
Re:2.4 ghz antennas (Score:1)
what was the noise temperature? (Score:5, Insightful)
Re:what was the noise temperature? (Score:1)
Re:what was the noise temperature? (Score:2)
Oh and several of the people on here mention leagal issues.....yeah there may be some, but I don't think that the equipment you have would do anything to push you close to the ERP. Most wirless networking stuff is pretty low power (come on it's being powered by a laptop....). Probably the most dangerous things from a legal standpoint would be spurious emissions. With a properly tuned antenna, you don't get these and that means a antenna with a good SWR (1:1 is ideal, but 1:2 can be acceptable). When an antenna is not tuned properly you can get harmonics OUTSIDE of the band and those harmonics sould be what causes you trouble.
What they need to try next is a yogi. (Score:3, Interesting)
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 [ve3gk.com]
Re:What they need to try next is a yogi. (Score:4, Informative)
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....).
Re:What they need to try next is a yogi. (Score:2)
Re:What they need to try next is a yogi. (Score:2)
Basically, if you want to do this stuff, get out your ti-85 and buy the ARRL antenna handbook and start learning.. antenna theory and RF calculus can be more fun than programming in lisp!
Re:What they need to try next is a yogi. (Score:1)
I've seen this done before.. (Score:2, Interesting)
Re:I've seen this done before- not the same thing. (Score:2)
Re:I've seen this done before.. (Score:3, Funny)
Re:I've seen this done before.. (Score:1)
the other side of the pillow (Score:5, Funny)
That's definitely a phrase I need to use more often.
Re:the other side of the pillow (Score:2)
This is what made America great in the first place (Score:1)
Of course, it's also funny as hell. Go geeks! :)
Re:This is what made America great in the first pl (Score:2)
I'de really like to know... (Score:1)
Re:I'de really like to know... (Score:2)
Check out http://trevormarshall.com/biquad.htm
I have the dish, I have the biquad, now I just need to marry them together and VERY high gain antenna, thank you.
"3 doublings"? (Score:1)
A Better Design.. (Score:3, Informative)
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.
Indeed- that's a really SLICK antenna there. (Score:2)
Re:Indeed- that's a really SLICK antenna there. (Score:3, Informative)
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.
Re:Indeed- that's a really SLICK antenna there. (Score:1)
In short: EIRP (effective isotropic radiated power) is regulated, directivity ("focusing") is significant, and the rules are different for directive and point-to-point systems. See here for an overview:
The FCC's Part15 Rules and Regulation and 802.11b emissions in the ISM 2.4GHz Band [lns.com]
power output (Score:1)
The regulations do state that if you use a more powerful gain antenna that you have to reduce your power from the maximum by a certain amount for each dBi above the allowed limit.
So in a sense the amount of focusing is limited.
However the Orinoco (Lucent) cards are not anywhere near the maxiumum power, so with a stock card you just can't get an antenna that will make you break the law.
To really do this right you need a bidirectional amplifier like made at hyperlink [hperlinktech.com]. A commercial antenna, lightning protector, low impedence cable, and professional adapters are handy too. Hyperlink sells nice kits with all of that.
Re:A Better Design.. (Score:2)
Re:A Better Design.. (Score:1)
and neither surpassed the performance of a Pringles can antenna.
The antennas in one pair were 1.5 ft long. The antennas in the second pair were 3 ft long. At a distance of 580 meters, the signal/noise ratio was
17dB using the short pair, 20dB using the long pair, and 25dB using a pair of Pringles can antennas. Also at 580 meters, we achieved 50dB signal/noise with parabolic dish antennas we bought mail-order.
recycling (Score:1)
arg! (Score:1)
...
God dammit mom! you recycled my networking equipment again!
now i know. (Score:1)
alls thats left is to level all obstructions inbetween the mile strech. That will be the fun part.
Those ain't no chips pardner! (Score:2, Funny)
Let's just say it doesn't come loaded with saddle-shaped styro-chips.
As any discerning antenna hacker knows, Pringles are CRISPS, not chips. Sheesh...
Directional Antenna (Score:3, Informative)
802.11b high gain antenna (Score:1)
Re:802.11b high gain antenna (Score:1)
1:increasing received signal at the demodulator input (preamplifier)
2:increasing antenna gain
3:reducing noise floor/increasing demodulator sensitivity.
Forget about number 3. If you're going to spend 60 bucks on a wireless card, the RF side is going to be shitty.
Number 2 is great, as it requires no extra *active* hardware, and it gives you the same boost on TX *and* RX, and it may help reject other signals (directional antenna).
Number 1 could be done, if you wanted to hack up a 2.4 gig preamp to automatically switch out of line when the card's transmitting. Best bet would be to get a tx/rx amp, boost your outgoing signal as well.
Antennas are my favorite solution. Simple, good projects, and super-effective.
Annoyed (Score:1)
But you have to admit they tried.... (Score:3, Informative)
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.
Re:Annoyed (Score:1)
Re:Annoyed (Score:2)
Quick definition please. What does SWR standfor/mean?
Re:Annoyed (Score:1)
Other tests (Score:2, Informative)
Old article, achieving 14km (Score:4, Informative)
Also reports of 57km achieved by Lucent engineers, staying within FCC specs.
-me
Re:Old article, achieving 14km (Score:2)
my homemade TV antenna :) (Score:2)
About 100 feet of 4-strand telephone wire run from TV, out the window, to the metal roof of a large shed some 50 feet away, with a large tangle of barbed wire hanging from one corner of the roof (the barbed wire seemed to be critical to reception).
It worked amazingly well. Tho it's a wonder the TV didn't blow up.
Of course, it wasn't nearly as portable as a Pringles can!
Re:my homemade TV antenna :) (Score:2)
Don't they have cable TV in prison yet?
Re:my homemade TV antenna :) (Score:2)
Simulate the antenna first (Score:3, Interesting)
This is funny... (Score:2)
...but I worked with a fellow back in the '80s who built, for his MSEE thesis, a stripline antenna out of pieces of a Coke can for a GPS receiver. As I recall, his thesis included photos of the antenna that showed enough of the Coca Cola logo that everyone could see what it was made out of. It was fun conducting tours of the labs and telling high school kids that ``this project here is tracking satellites with an antenna made from a Coke can''. Loved the look on their faces. (Wonder where Sam is now...)
He tested it on Valentine's Day. (Score:1)
He may have too much time on his hands, but at least he knows how to spend it. Who needs romance anyway??? Right, CmdrTaco?
;-)
Check out Girl Geek's journal. [slashdot.org]
Re:He tested it on Valentine's Day. (Score:1)
The Adventures of Girl Geek! [slashdot.org] Comments enabled.
Re:Attn: HR - please discard (Score:1)
savvy
know. -n. knowingness; understanding.
[Pidgin alteration of Spanish sabe usted
you know]
Re:Attn: HR - please discard (Score:1)
Re:on Valentine's day? (Score:1)
Re:Big can of stew (Score:2)
Some of my favorite foods are vegeterians