bmoore314

Here is some pictures of some antennas i made/use the one on my compaq laptop is just taken from a mac g4 case, it worked ok, good for a really portable setup. The other two I designed, using calculations from the ARRL Antenna book, very useful book. Anyways here they are, the cans are dole pineapple cans, work well and are about the right size for an efficient waveguide.

http://www.forgottenfords.org/antenna.jpg

http://www.forgottenfords.org/myant.jpg

http://www.forgottenfords.org/newant.jpg

gcrocker

I just got some metal air conditioner duct for my next cantenna. It comes in 3" and 4" diameters, 48" long (or longer if you want). I haven't made one yet, but I think it's going to kick ass. There are even caps, though 5" was all I could find at Home Depot.

-glenn

bmoore314

If I remeber correctly, 3"-4" is the right range of size the waveguide needs to be for the most efficient waveguide in 2.4 ghz. The pineapple cans I used are about 3.5" diameter, and are around 4.5"-5" tall. When I get home, I'll put in the 3" and 4" and try and get you the correct placement for the probe in the can (probably around 4" from the back). The antenna book is awesome, and has all the formulae required to make a very efficient can. Just for some comparisons of my design, the 2 pineapple can design works about equal to or maybe 1-2db SNR better than the long pringles can design, and had similar directivity. 4 pineapple cans gave me about 3-4db better SNR in stumbler, but was noticeably more directional than the 2 can design. The 2 can design with a cone collector on the end works significantly better than the 4 can desgin, giving me 4-5db SNR over the 4 can design, and 8-9db SNR over the pringles can. It also was less directional than the 4 can design, but still more directional than the pringles can.

gcrocker

Interesting numbers. Thanks!

Here's a nice site with some Javascript that'll do the probe placement calculations (and likely frequency range for a given can diameter):

http://www.turnpoint.net/wireless/cantennahowto.html

-glenn

lincomatic

bmoore314, thanks a lot for the info. interesting numbers.
so the ARRL antenna book is a good resource for designing microwave antennas as well? i haven't been able to find a copy to peruse in the local bookstores before buying it...but you may have just pushed me over the edge

btw what are the dimensions of the screen funnel? is accuracy critical when making it?

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~lincomatic

bmoore314

For the cone, it is 3.5" diameter at the can, and 11" diameter at the openeing. I used coat hangers, with a wire screen for it. The coat hanger between the two circles is 7.5", didn't really measure how far out it ended up. The important part is that the angle of the cone needs to be about 30 degrees. I chose 11" because thats about the diameter of one of thoes huge economy size white soap buckets, which i have alot of lying around. The opening could be as large as possible, but the larger you make it, the more transmit power you need, but the better your recieve signal will be. The correctness of the collector isnt as critical as the dimensions, and probe placement in the can, but the closer to perfect, the better the performance will be. Mine didnt turn out very good, but the performance was still pretty good. For the transmit, recieve power, using an 11" opening gives me better recieve than transmit. It ends up being weird while trying to aim, because I can get a decent signal in stumbler, but end up not having a good connection, because the other end isnt seeing my packets. The other end is an omni directional antenna, so if you were doing two antennas, the extra recieve power would probably make up for the connection. Anyways, I now aim my antenna using ping instead of stumbler, and aim it for the least ammount of packet loss.

The antenna book has quite a lot of information on antenna design, and most of it will scale to microwave. It has a small section on microwaves, and high frequency, but not a whole lot. I would still recommend getting it, there is lots of good information about radio transmission in general, and it has been immensely helpful in all my antenna designs. Another book that has lots of good information is the ARRL UHF/Microwave experimenter's manual, antennas, components, and desgin. It has lots of good information, and some on building amplifiers as well, and it is only $20. A third book, with good information on building amplifiers and stuff is the ARRL Uhf/Microwave Projects manual. It doesnt have any antenna information in it, but it has lots of good amp projects, its also only $20. I picked up all the books at a local ham shop, along with my cable. I think I will take some more pictures of the can with collector antenna tonight, and take some of my pringles antenna, which is the design that has some of the reflector outside of the can as well.

Other parts of my setup are an orinoco silver card, cheap pigtail from ebay that broke after like 3 or 4 uses, that I managed to solder back together, 10 feet of RG-8X, Silver N connectors on the cable (expensive, like 8 bucks each), and my main machine is a emachines eOne. The eOne is a great computer for a base station, it has 2 pcmcia slots built in, and an ethernet card built in. Very cool. I am hoping to build/buy an amlifier sometime, but I am really broke right now and I can't afford it. Some other nifty things that are on my wish list is an SWR meter and a spectrum analyzer, to help with antenna tuning, and amp tuning. Anyway, thats the end of my long post, questions/comments would be welcome and apreciated

bmoore314

Also, good site for the javascript calculations, it matched up from what I got in the antenna book. I like the antenna book cause it has the formlae for it, and more explanations on how they work. I think my next antenna design is going to be a helical design, giving a circular polarization. Hopefull that will be able to extend the range and overcome some of the interference in a residential area. It should only lose a few db from the mismatched polarization, but should do slightly better when it comes to reflections and such

lincomatic

thanks. your last post was a veritable treasure trove of info.

that's interesting...i didn't realize that the cone would cut the transmit gain while increasing the receive...but i guess it makes sense that i would spread the signal over a wider area.

i haven't been able to find any cans with smooth sides or flat bottoms...all i could find have ridges...do you think that affects the gain in a noticeable fashion?

i've been trying to decide which ARRL book to get, the Antenna Book or the UHF/Microwave experimenter's manual; my budget doesn't allow me to get both. if i were only to get one, which one would you recommend? can u give me a brief synopsis of what kind of antennae are discussed in the UHF/Microwave book? i've found lots of homebrew designs on the net, but very few analyses of the designs (i.e. formulae use to design them).

have you tried any antenna modeling software? i'm just getting started with NEC2, but it's very time consuming to input the designs.

are you using the eOne as your base station? what kind of AP software are you using?

thanks for your help sorry to swamp you with questions. btw, in case you haven't seen it, there is a homebrew antenna thread in the hardware section of the forum:

http://forums.netstumbler.com/showth...&threadid=2034

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~lincomatic

bmoore314

For the antenna cans, I think most ridges in the cans are small enough that they dont affect the signal that much at all. They are usually really small, in the 2.4 ghz range, the wavelength is about 13 cm, and 1/4 wave is close to 3 cm. the ridges on cans are (guessing here) about 1/2 cm or less, which shouldnt cause a significant ammount of loss. Altho it isnt much of an affect, there is some. Perfectly smooth would be ideal, but at the power levels of wavelan, you probably only lose about 1-2 db if even that. I havent tested, just guesstimating.

With the ARRL books, the uhf/microwave book has basically yagi's, parabolic, helical, and some waveguide/dish feed designs. I feel that the uhf/microwave book antenna section is really just a supplement to the antenna book, and it repeats some information as well. It doesnt really provide a whole lot on calculations for antennas, just gives you dimensions based on wavelength and such. I would suggest getting the antenna book first, it has more explanations, and information on the antennas, and calculations and graphs, and then at a later time get the uhf/microwave book later. I bought the antenna book first, and the microwave book afterwards. For antenna design, the uhf/microwave project book is not usefull at all, it mostly has amplifiers and transverters. The experimenters book has some circuit desging information(tuning, trace width etc.) as well as a section on antennas.

For the transmit and recieve power, basically the larger the antenna you have, the more power you need to give it, because the signal is more spread out. There is also some more things to have to do with it, which im not quite sure of but my dad, who was a radar tech in the air force, also agreed with my observations on recieve/transmit powers with the antenna size. I think one analogy that might be somewhat similar relating to power requirements is stereo speakers. A small tweeter doesnt require much power to be heard, because there isnt much to vibrate, while a subwoofer requires a substantial ammout of power to be heard as well. Sound frequency plays a part with that, but just the ammount of electrical energy required gets larger as the size increases. This probably isnt a *great* analogy, because sound frequency and stuff has an affect, but you get the idea.

My eOne isn't running as a base station, its just using the orinoco client software, connecting to another network and using the NAT function in wingate to gateway to the other network. I also have a linux machine, running a prism card in peer mode acting as a 'base station', bridging local wireless machines to my physical network. I could set the linux box into AP mode, but with this card, the farthest machine away couldnt get a signal, for some reason in peer mode it works fine. The linux box is using a SMC card and the far machine uses a linksys card (or the other way around, i dont remember) The orinoco cards connect fine to it as well in peer mode. Hope that awnsers all your questions

bmoore314

I just noticed in my previous post, I said it would be about 4" from the back, I meant it would be about 4cm from the back. Anyways, here is some pictures of my pringles antenna. I found that the pringles can wasnt sufficiently strong enough to hold the longer reflector stable, so i used some plexiglass pieces to make for easy holding, and stability. Worked well, but it didnt do very well in the rain, got soggy and now the probe moves around some (very bad thing) I don't really use it much anymore, the cans are definately better. Also is another picture of my pineapple antenna with collector. (the collector isnt as bent looking as the picture seems to show, its just a trick with the light on the mesh)

http://www.forgottenfords.org/pringles1.jpg

http://www.forgottenfords.org/pringles2.jpg

http://www.forgottenfords.org/collect2.jpg

lincomatic

i've already ordered the antenna book at borders.

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~lincomatic

Fritzo

Yikes....is every antenna maker in this forum such a SLOB???? Man....those rooms were filthy! Call your moms and have them clean that mess up! Heheheheheeh....

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Maybe in order to understand mankind, we have to look at the word itself: "Mankind". Basically, it's made up of two separate words - "mank" and "ind". What do these words mean ? It's a mystery, and that's why so is mankind.

blackwave

I just looked at the photos... I have to admit I had trouble focusing on the intended object. I also have learned that organic matter and computers shouldn't mix. In the past though I have had to sleep on computer parts and books... but that was generally because the mastermind in my head decided to start looking for some type of adapter that i know I had and spent 5 hours looking for it before passing out...


Overall I have seen worse, and let me tell you that seeing it is a lot better than smelling it..

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-=BW=-

ARPAN3T

bmoore314--

i too am in the South Bay. Where is this local ham radio shop you speak of? I wanna spend my U.S. dollars!!!

bmoore314

Its in sunnyvale, off lawrence, near the disk drive depot. close to lawrence and central expressway.

My room isnt always a disaster, just most of the time :P