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O'Reilly's Antenna Shootout 149

Posted by timothy
from the my-that's-a-large-can dept.
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.
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O'Reilly's Antenna Shootout

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  • If you're doing no better than omni, you may have an impedance mismatch to overcome. Pattern might be just fine.
  • Antenna? (Score:4, Funny)

    by 5arah (308173) on Saturday February 16, 2002 @11:15PM (#3020525)
    They should get together with the Sliiiiiiiiiiiiinky [firstpr.com.au] guy. Although there might be issues with reception..."HEY MAN! Quit shaking it!"
  • Waveguides? (Score:3, Informative)

    by icqqm (132707) on Saturday February 16, 2002 @11:16PM (#3020528) Homepage Journal
    They certainly don't look like Yagi antennas. But even then, wouldn't dishes be better for this sort of thing? I just can't imagine how a Pringles can can radiate power like that without reflecting a lot of it back.

    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.

  • Does this really do the job? I know nothing about wireless networks (even though mine works great) but I have to wonder if beefing up one end of the system really works.

    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?
    • What to prevent you from installing this on your laptop also (providing you can remove the antenna)?

      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)

      by Lumpy (12016)
      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.
      • Uh, that's 0.25 dB/foot.

        That's losing half your power (3 dB) every 12 feet.

        --Blair
      • by rcw-home (122017) on Sunday February 17, 2002 @12:46AM (#3020718)
        First off, at 2.4ghz RG58 loses .25db/ft, not 2.5db/ft.

        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.

        • Remember, 100db gain means 10 million watts of effective radiated power for every milliwatt of input power.

          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
        • First off, at 2.4ghz RG58 loses .25db/ft, not 2.5db/ft.

          What he said is:

          RG58 has a 25db loss per 100 foot at 2.5ghz

          But then he says:

          ...that is 2.5db per foot

          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?
          • Yeah, math at 3am creates foggy thinking and everything is off by one decimal point. Which also skewed my antenna gain calculations... I was including the gain of the feed-can in the antenna dish gain... effectively tripling the gain numbers.

            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.
        • Rob Flickenger confuses a few numbers in his article, but this should not discourage anyone from trying to make an antenna. Remember, a db (decibel) figure is simply a ratio. positive dB means gain, negative dB means loss. He uses the sample of 9dB equalling a power gain of about eight. The actual figure is closer to 7.94, the antilog of .9, and anyone who points this out should be shot. -9dB would be a power attenuation of 8 to 1. He also talks about dBm, which is the ratio of power to one milliwatt and dBi, which is gain or loss relative to a perfect lossless antenna (isotropic). You can buy one of these at the same store that sells frictionless bearings and perfect insulators. That being said, you may safely ignore it. Rob gives tables of figures showing that some designs have better performance than others. His measurements are crude, and hardly suited to a college thesis. The reader who complained about not seeing noise temperature did not understand the tables or the measurements. Noise temperature was lumped with other noise, a perfectly acceptable way to get data for quick comparisons. I was involved in building telemetry antennas on a government project once. We had the guidance of an experienced professional engineer who taught us the basics and had proper test equipment for checking voltage standing wave ratios at any frequency we wanted. The antennas were built from scrap metal, broken connectors, welding rods, scrap coaxial cable, and anything else we found useful. We could prove them to perform equally to commercial antennas costing hundreds of dollars. Rob is telling you how to build good antennas cheaply. If you want parabolic antennas with hyperbolic reflection to the base of the parabola, feeding a low noise preamplifier to your network card, then build it. If you can do so cheaply, publish. Others may want their own. But don't snipe at the man who has a cheap working solution until you can show how to improve it.
      • Re:Serious question (Score:3, Interesting)

        by SectoidRandom (87023)
        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 [d128.com] 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.
    • Re:Serious question (Score:2, Informative)

      by doctorjohn (528164)
      Serious answer: http://www.borg.com/~warrend/guru.html
    • Does this really do the job? I know nothing about wireless networks (even though mine works great) but I have to wonder if beefing up one end of the system really works.

      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.... ;) The big iron in the banks in that NZ harbor went down real quick. These things can light up flourescent light tubes from km's. Hell, these RADAR's have to emit enough power to light up an inbound missle skimming the ocean, a missle with a REALLY small RADAR reflection coming up over the horizon at around 30km. Admittedly, with those things travelling at the speeds they do, the doppler effect tends to cause them to stand out like dogs balls. But the Navy would still like to know about anything and everything around them, a lot further than 30km, if it is stupid enough to be flying high enough that is.

  • Is there anything on the books (FCC, et al.) now that would stop me from *legally* implementing any of these solutions?

    (And I'm not talking about ISP usage agreements and such.)
    • Is there anything on the books (FCC, et al.) now that would stop me from *legally* implementing any of these solutions?


      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.
    • by Phork (74706) on Saturday February 16, 2002 @11:51PM (#3020604) Homepage
      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
  • The only question I have is when Georgia Tech (my school) will ban pringle cans on top of dorms...

    DAMN would a 802.11b network be cool to run there... Massive internal gnutella network, here we come!
    • Gnutella network? Maybe you should consider using Nutella [nutella.it] jars then!

    • Makes you wonder.. which uplink is LAWN using? Considering Resnet/Eastnet's is HOSED, it's possible that LAWN is on the academic feed :)

      Internal bandwidth is not an issue, here (small house, eastnet). I can pull 900K to/from unloaded internal sources.
  • Wouldn't a conical waveguide work a little better? A dish would be best but probably rather large for the band they are trying to operate in.
    • Re:Conical waveguide (Score:2, Informative)

      by GregWalrath (9458)
      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.
  • a dish? (Score:3, Interesting)

    by itzdandy (183397) <dandenson&gmail,com> on Saturday February 16, 2002 @11:37PM (#3020572) Homepage
    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.
    • Re:a dish? (Score:4, Interesting)

      by Phork (74706) on Saturday February 16, 2002 @11:55PM (#3020614) Homepage
      You could use two antennas, but it is not as simple as connecting the wires, you need to use a 2 to 1 RF transformer meant for 2.4ghz, but there are plenty of these devices made these days because of the proliferation of 2.4ghz devices. I see them advertised in rf design all the time.
    • Re:a dish? (Score:2, Insightful)

      by IsaacW (543020)
      i believe the FCC limits these 2.4Ghz signals to 100dB

      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!
    • These cans are meant to concentrate the signal unidirectionally. If you put one on your dish it might amplify the signal, but only if it were aimed very precisely at the satellite. It would probably be tough to get things aligned properly, but I don't know since I've never tried it.
    • A waveguide antenna feeding into a dish reflector is called a feedhorn. They work very well.
  • explinations... (Score:5, Informative)

    by Lumpy (12016) on Saturday February 16, 2002 @11:43PM (#3020587) Homepage
    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)
    • > The pringles can is nothing more than a basic
      > 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.
    • The metallic layer of a Pringles can most certainly is conductive. You have to poke through a plastic film to get to it, though.

      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)

    by Skuld-Chan (302449) on Saturday February 16, 2002 @11:54PM (#3020611)
    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/ [n3iyr.com]
    • The trouble is, the feeds used on these antennas are helical polarization. Most 802.11b antennas use either vertical or horizontal polarization.

      Of course, you can still use two of the n3iyr antennas, one one each end. Or have the other end use a helical antenna.
      • ah true - I just know this guy from my experience using amatuer sattelites :) - I've never actually worked 2.4 ghz before, but he definately has a nice solution.

        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.
      • Oh just remembered - one thing you could do is change the feedhorn out for a more traditional Ku style antenna (same band mostly). I think most dbs dishes (like direct tv and dish network) have these kinds of antennas already. Not sure how they are polarized though.
        • I once tried to use a Ku band dish for 802.11b, with the stock feedhorn. It didn't work; although the feedhorn worked great for recieving it didn't transmit very much, if at all.
      • Re:2.4 ghz antennas (Score:3, Informative)

        by Technician (215283)
        Be sure to get a pair that are the same polarization. You change polarization only when the signal is reflected. Same = line of sight. Oposite = bounced off a reflector or passive repeater.
      • One big advantage of circular polarization is that it will talk to both horizontal and vertically polarized antennas. You do have to make sure that if you're using two circularly polarized antennas, that they have the same sense, i.e. LHP or RHP.
    • I'm trying to pick up what I can on this topic... I know very little, but learning. So I have some basic questions.

      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?

      • Yeah - I recomened it because I am an amatuer radio operator where the legal limit is technically 1500 watts - although I think it is much lower on that band (not to mention if you plan on running 1500 watts you'll require a station inspection)

        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.
        • I see as you say your coming from the amatuer radio world, but 150Watts at 2.4Ghz is a heck of a lot as I understand it! :) The legal limit in the free unlicenced 2.4Ghz spectrum is 4Watts yes four.
    • We've been doing some experiments at our local HAM club - check out: FRARS Homepage [frars.org.uk] and for wlan stuff: FRARS wlan pages [frars.org.uk]
  • by yoghurt (2090) on Saturday February 16, 2002 @11:55PM (#3020615)
    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.
    • Its on the second page: http://www.turnpoint.net/wireless/antennas/perform ance.html
    • Oh so true. The whole article shows a lack of knowledge. That and he probably does not have a way to measure SWR at this frequency or even know what SWR is at least before he wrote the article. SWR can kill your radio....literally. Although, the frequency at this wavelength does make it a bit easier to disregard SWR a bit because there are alot of losses just in the feedline (no such thing as a lossless feedline). If your measurements are close to being the right wavelength (1/4, 5/8 or Full Wave), you should be close enough to have a decent SWR. To maxmise your power, you really should look into getting or building a SWR meter.

      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.
  • by ubiquitin (28396) on Saturday February 16, 2002 @11:55PM (#3020616) Homepage Journal
    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 [ve3gk.com]
    • by Chanc_Gorkon (94133) <gorkon AT gmail DOT com> on Sunday February 17, 2002 @08:17AM (#3021297)
      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....).
    • it's not a yogi... someone duped you with a word they made up. It's called a log-periodic beam antenna. been around for about 50 years. Hams have been using them and all of the home TV antennas you can buy (you know the big aim-able ones) are all log-periodic antennas.

      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!
    • What I want to know is why anyone would want a Yogi antenna when you can have a Boo-Boo antenna... it costs the same but it's smaller and doesn't require as much maintenance.
  • But with slightly different subject matter, and a different set of suckers. See here. [northwestern.edu] It's amusing to see this kind of hoax fool people.
    • In this case, I doubt it's a hoax. The soup cans comprise a waveguide/feedhorn at the frequencies that the 802.11 cards operate at. Certain cans (such as old Hi-C cans) are fairly good feedhorns because they're shaped right and are the right length to get a good signal in them. I know, HBO used to use 2GHz beamed signals to households (Before cable was prevalent- it was more economical than satellite, etc.) and there was plans, etc. out at that time to snag the signals they were sending out so that you didn't have to pay the monthly service fee for the rig they were using to broadcast it. The varying plans for these recievers usually included an antenna design using a certain sized Folger's or Hi-C can for a feed horn and a metal dish sled for the parabolic reflector. Worked pretty good as a makeshift 2GHz antenna. I'm sure the feedhorn part would make for a decent unidirectional range booster for an 802.11 card with an antenna jack.
    • 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.
      • You, too, miss the point that Dinda and Placeway had in inserting those entries. From a Zephyr message by Dinda following up the letter being published by Stereophile:
        The "moose", along with "Squid in vegetable broth" and "evaporated

        haggis", were an attempt to make it obvious that we were kidding.
        Perhaps they should have tried a little less subtle satire for the benefit of less sophisticated readers.
  • by Dr. Awktagon (233360) on Sunday February 17, 2002 @12:01AM (#3020631) Homepage

    ...this design for a do-it-yourself, VERY inexpensive antenna made from the a recycled junkfood container is as cool as the other side of the pillow.

    That's definitely a phrase I need to use more often.

  • And it's sad to think that we'd let corporate interests stamp out this kind of experimentation and hardware hacking because it interefered with their conception of intellectual property.

    Of course, it's also funny as hell. Go geeks! :)

  • ...about using old DSS/Primestar dishes for this type of thing. You should be able to pick up the dishes for cheap/free now a days. Would anyone care to post some links to resources on this subject?
  • why not just 8x?
  • A Better Design.. (Score:3, Informative)

    by thesupraman (179040) on Sunday February 17, 2002 @01:18AM (#3020782)

    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.
    • But the question remains, does attaching this higher performing antenna end up exceeding the effective radiated power beyond the limits set by regulations? If it does, you've got problems. The soup can doesn't and gets passable gain improvements over a bare card with a diversity antenna.

      • 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.
        • This topic was covered [slashdot.org] in the Cringley Bank Shot discussion.

          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]
        • 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.

    • I read the article and you can tell the builder of this PVC-pipe antenna must have really read up on antenna design (ARRL antenna design handbook or something similar). This antenna will definitely way out-perform the food can antennas by a substantial margin.
    • I have tested two pairs of these helicals,
      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.
  • lol. I worked for Procter and Gamble Global IT for the past couple years and we've been experimenting with wireless deployment at certain locations. I wonder if it would be more cost efficient to recycle our Pringles cans toward this operation. It'd be fun to see Pringle's can antennas all over the place. Nice way to recycle.
  • by feldkamp (146657)
    hmmm... why isn't the network up....
    ...
    God dammit mom! you recycled my networking equipment again!
  • Now i know to use a chunky beef stu can to set up a wireless network to my friends house.

    alls thats left is to level all obstructions inbetween the mile strech. That will be the fun part.
  • Quoth the editor:
    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)

    by Pass_Thru (79608) on Sunday February 17, 2002 @04:07AM (#3021045)
    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!
  • while we're discussing cheap, homebrew antennas to increase TRANSMISSION range, has anyone successfully modified an 802.11b laptop card to increase the range at which it will receive a signal?
    • That would be very difficult. "Increasing reception range" usually means one of three things:

      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.
  • by drwho (4190)
    Instead of screwing around with tin cans, wlan enthusiats would be better off learning real antenna design, and building something appropriate to their situation. In addition to the blind and ignorant 'dB gain' that the slashdot wlan crowd seems to be fixated on, an intelligent consumer would be concerned with the beamwidth, the front/back ration, SWR, and the bandwidth of an 802.11 antenna, and not the oversimplified, crude, and possibly harmful (SWR too high can break radio gear. This may include your 802.11b card) pringles-can type of gear that seems to get a lot of geek press. This doesn't mean that you have to spend hundreds of dollars on a Lucent Orinoco antenna just ot have decent performance, but you do have to do some research into figuring out what you need, and then find a vendor that will provide you that at a reasonable price. guerrilla.net provides provides free plans for an engineered antenna (as opposed to the gross hacks which appear here). Yes it's an omni. Still, you may get better performance, because not so much of the signal is wasted due to poor SWR!
    • 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.
    • As a radio engineer, I am with you. The design procedures featured on the site, as well as the performance indicators, are abominable. The designs they propose will never be better than a real antenna, but at least they're trying. While a hacked antenna requires little intellect to "design", it requires consequently less intellectual invenstment as well - no need to learn field equations. At least it keeps them happy and out of our hair.
    • Quick definition please. What does SWR standfor/mean?

      • IIRC it's standing wave ratio, or put another way the proportion of power bounced back from the antenna to the transmitter. That's why the impedance mismatch is so bad. If the SWR is really bad you can blow the output stages of the transmitter because the RF power is absorbed at the transmitter instead of being radiated. (Oversimplified to excess by a chemist.)
  • Other tests (Score:2, Informative)

    by xof (518138)
    You can find other 802.11b antenna experiments in Finland [saunalahti.fi] and in Belgium [reseaucitoyen.be] with HomeMade antennas [reseaucitoyen.be] (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 [bigpond.net.au]) or not. I've got some other links here [skynet.be] And, just a note about dB's : adding 6 dB allows you to double the distance.
  • by PhotoGuy (189467) on Sunday February 17, 2002 @10:35AM (#3021502) Homepage
    Here's [mac.com] 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
  • Once upon a long time ago, I lived a day's hike from any TV stations, and was too broke to buy a real TV antenna. So I made one out of what was to hand:

    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!

  • by LM741N (258038) on Sunday February 17, 2002 @02:04PM (#3022184)
    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.
  • ...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...)

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