Two questions-usb;antenna construction, please help?
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Posted by bubblebrain on December 26, 2008, 2:26 pm
Please log in for more thread options Besides proper curvature and whip focal point placement, what other factors are critical to home made construction of an aluminum foil u-shaped (approx) parabolic antenna? I'm getting an ok signal but wish to improve on it. The lead to the antenna is very short, small wire (indoors), should I maybe try to shield it better? This was made from schematics to insure the proper curvature and is about 1 foot wide and 1/2 foot high with 5 inch whip inside at focal point approximately. I used cut foam forms to shape it, the shape is not perfect, but close and aluminum foil to line the inside. I am aiming it from inside a picture window with metal venetian blinds, which amazing do not seem to make a difference if the are open or closed??? I am using a good pcmcia card with this on a laptop. To get my desktop going, what is the strongest radio I can buy in usb or other for it? I have about 8 feet to go to the computer from the same antenna. The transmitting signal I believe is quite strong, municipal, but the problem lies in receive sensitivity. Sorry if this has been covered somewhere, if you have the links to the discussion? Thanks. | ||||||||||||||||
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Posted by Jeff Liebermann on December 26, 2008, 7:15 pm
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Yes. The USB dongle is not an idea feed for a reflector (dish, corner reflector, flat plate, etc). You will get a gain increase, but not as much as could be obtained with a proper feed. Also, the gain will be different in xmit and receive. That's because much of the RF radiated by the USB antenna will go in undesireable directions. See thread at: <http://groups.google.com/group/alt.internet.wireless/browse_thread/thread/7490a07cdc3cfac7>
for clues.
>I'm getting an ok signal but wish
>to improve on it. Even a flat plate reflector will improve the signal. Try it. Piece of aluminum foil located behind the USB dongle. >The lead to the antenna is very short, small wire
>(indoors), should I maybe try to shield it better? Ok, time for a rant. WHAT MAKE AND MODEL USB CONTRIVANCE DO YOU HAVE? It's bad enough that you don't bother to supply a single number (signal is "ok", lead is "short"), but if I have to guess whether your contrivance is a USB ethernet bridge or a USB dongle, I'm out of bright ideas. If you're talking about the USB cable, the limit is about 5 meters. Shielding the USB cable will not have any effect performance. It's already shielded anyway. >This was made from
>schematics to insure the proper curvature and is about 1 foot wide and >1/2 foot high with 5 inch whip inside at focal point approximately. Schematics are for electronic components and wires. I think the correct word is "template". Got a URL where you found it? Photo? Is it this one? <http://www.freeantennas.com>
If so, which version did you build?
You'll have the same problem with a "5 inch whip" antenna as the USB dongle. Much of the RF goes in directions that do not hit the reflector. >I
>used cut foam forms to shape it, the shape is not perfect, but close and >aluminum foil to line the inside. I used to think it had to be very accurate to work. That's true if you want to squeeze every last fraction of a dB of gain out of the antenna. However, your can be very sloppy and it will still work better than the "5 inch whip" alone. >I am aiming it from inside a picture
>window with metal venetian blinds, which amazing do not seem to make a >difference if the are open or closed??? How far apart are the blinds? Are they metal or plastic. If horizontally polarized, the RF will go right through the blinds without hardly any attenuation. However, if vertically polarized, the horizontal blinds will block some of the signal only if they are less than 1/2 wavelength (6.3 cm) apart. Usually, the blinds are slighly less than 4 cm apart so there will be some attentuation. If they're made of plastic, RF goes right through them. >I am using a good pcmcia card
>with this on a laptop. What maker PCMCIA card? What model PCMCIA card? What laptop? What OS? What does this have to do with a USB antenna? >To get my desktop going,
What desktop? You started with what I guess is an access point, then switched to a USB something, then threw in a PCMCIA card in a laptop, and are not working with a desktop. Do you seriously expect me to follow your question(s)? >what is the strongest radio I can buy in usb or
>other for it? Strongest as in most powerful transmitter? Biggest antenna? Best quality? I can't supply a specific answer but in my experience, the range of a wireless system is primarily determined by the antenna. If you can get a decent directional antenna, pointed in the right direction, almost any radio will work. Also, it would be of some interest to know if you plan to install this radio inside the desktop or is external acceptable. Price range? How far are you going to try and communicate? What's on the other end of the link? Any walls in the way? If so, what are they made from? >I have about 8 feet to go to the computer from the same
>antenna. Ummm... please fix the English. Which antenna? Coax or USB cable? 8ft is not very far away, so the thin coax found on some external antenna will work. You could use a cheap PCI internal card, and add an external antenna. However, you haven't disclosed what's at the other end of the link, how far away, how many walls, etc, so I can't be sure this will work. >The transmitting signal I believe is quite strong, municipal,
>but the problem lies in receive sensitivity. Ok, so you're trying to connect to a municipal wireless network. How far away? Line of sight? Anything in between you and the access point? Can you install a directional antenna? Incidentally, what problem and who's receive sensitivity? The municpal networks sensitivity or your proposed hardware? >Sorry if this has been covered somewhere, if you have the links to the
>discussion? Thanks. Suggestion: Please get organized and don't try to mix too many questions together without a clear division. Also, models and numbers are a good thing. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 | ||||||||||||||||
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Posted by bubblebrain on December 27, 2008, 12:23 am
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Go back and read the OP, cuz I don't think you did not understood what I said, or more likely you began answering before you had read the entire post. Maybe I was not clear or not using the proper terminology. Let me try to clarify. I am getting a 40-66% signal strength using a wubber ducky pole antenna with a parabolic reflector behind it. I was asking what construction factors, other than the ones I already know about (proper curvature and placement of the wubber duckey pickup at the focal point) might maximize the reflector efficiency. Reflective material used (using alum foil now), size; what common mistakes are mostly made in homemade construction of these? It is already about as large as I want it to be for indoor use at about 2' by 1' The wubber duckey is about 7 inches long. Second question is which brand/ model of usb dongle has the best transmit receive sensitivity (more important) for use with the same reflector and my desktop computer. I cannot obviously use the pcmcia card with my desktop since I have to go about 10 feet to it and it is designed for laptops. Now I recall that seattle wireless did some testing of these, which I have to revisit, but their tests were not very comprehensive as I recall. I have no idea where the APs are, a visual survey of the area saw no tell tale antennas, one AP I am guessing is far away on a tower about 50 feet high, probably about 3 miles away. No line of sight, so I have no idea what is between us. I have at least 2-3 independent signals I can connect to, so the relevant question is what can I use for the desktop radio and a good usb radio is what comes to mind. I live in an apartment complex, so I am stuck with an indoor reflector or antenna. Since I don't have a line of sight, I am guessing that a dish antenna will not work, since I have no reference point to point it to, nor do I know what lies between me and the AP. I am not going to buy fancy signal detecting equipment for this, it's a shoestring operation. The venetian blinds are oriented horizontally, and metal as I said before, but their adjustment makes little to no diff in signal strength. I'm not going to tell you my OS, radio make, etc. That is information that can conceivable could be used to identify me individually and I don't want that, thanks. I have doubts that there exists a usb dongle on the market that will match the receive sensitivity and transmit power of the pcmcia card I am using. Most users report they are weaker. If you have any concrete suggestions on how to maximize the efficiency of the usb dongle, please state them. At this writing I don't know what else I can use with the desktop since I have to go about 10 feet to it and cannot install an outdoor antenna in these apartments. Maybe a USB with a dish reflector behind it might be worth a try, all homemade. Have seen some cool ones made from an umbrella. You really did not answer my questions, but you did make me think about it more completely, so now I know what to research. > wrote:
> >>Besides proper curvature and whip focal point placement, what other
>>factors are critical to home made construction of an aluminum foil >>u-shaped (approx) parabolic antenna? >
> Yes. The USB dongle is not an idea feed for a reflector (dish, corner > reflector, flat plate, etc). You will get a gain increase, but not as > much as could be obtained with a proper feed. Also, the gain will be > different in xmit and receive. That's because much of the RF radiated > by the USB antenna will go in undesireable directions. See thread at: > <http://groups.google.com/group/alt.internet.wireless/browse_thread/thr > ead/7490a07cdc3cfac7> for clues. > >>I'm getting an ok signal but wish
>>to improve on it. >
> Even a flat plate reflector will improve the signal. Try it. Piece > of aluminum foil located behind the USB dongle. > >>The lead to the antenna is very short, small wire
>>(indoors), should I maybe try to shield it better? >
> Ok, time for a rant. > WHAT MAKE AND MODEL USB CONTRIVANCE DO YOU HAVE? > It's bad enough that you don't bother to supply a single number > (signal is "ok", lead is "short"), but if I have to guess whether your > contrivance is a USB ethernet bridge or a USB dongle, I'm out of > bright ideas. If you're talking about the USB cable, the limit is > about 5 meters. Shielding the USB cable will not have any effect > performance. It's already shielded anyway. > >>This was made from
>>schematics to insure the proper curvature and is about 1 foot wide and >>1/2 foot high with 5 inch whip inside at focal point approximately. >
> Schematics are for electronic components and wires. I think the > correct word is "template". Got a URL where you found it? Photo? > Is it this one? > <http://www.freeantennas.com> > If so, which version did you build? > > You'll have the same problem with a "5 inch whip" antenna as the USB > dongle. Much of the RF goes in directions that do not hit the > reflector. > >>I
>>used cut foam forms to shape it, the shape is not perfect, but close >>and aluminum foil to line the inside. >
> I used to think it had to be very accurate to work. That's true if > you want to squeeze every last fraction of a dB of gain out of the > antenna. However, your can be very sloppy and it will still work > better than the "5 inch whip" alone. > >>I am aiming it from inside a picture
>>window with metal venetian blinds, which amazing do not seem to make a >>difference if the are open or closed??? >
> How far apart are the blinds? Are they metal or plastic. If > horizontally polarized, the RF will go right through the blinds > without hardly any attenuation. However, if vertically polarized, the > horizontal blinds will block some of the signal only if they are less > than 1/2 wavelength (6.3 cm) apart. Usually, the blinds are slighly > less than 4 cm apart so there will be some attentuation. If they're > made of plastic, RF goes right through them. > >>I am using a good pcmcia card
>>with this on a laptop. >
> What maker PCMCIA card? What model PCMCIA card? What laptop? What > OS? What does this have to do with a USB antenna? > >>To get my desktop going,
>
> What desktop? You started with what I guess is an access point, then > switched to a USB something, then threw in a PCMCIA card in a laptop, > and are not working with a desktop. Do you seriously expect me to > follow your question(s)? > >>what is the strongest radio I can buy in usb or
>>other for it? >
> Strongest as in most powerful transmitter? Biggest antenna? Best > quality? I can't supply a specific answer but in my experience, the > range of a wireless system is primarily determined by the antenna. If > you can get a decent directional antenna, pointed in the right > direction, almost any radio will work. Also, it would be of some > interest to know if you plan to install this radio inside the desktop > or is external acceptable. Price range? How far are you going to try > and communicate? What's on the other end of the link? Any walls in > the way? If so, what are they made from? > >>I have about 8 feet to go to the computer from the same
>>antenna. >
> Ummm... please fix the English. Which antenna? Coax or USB cable? > 8ft is not very far away, so the thin coax found on some external > antenna will work. You could use a cheap PCI internal card, and add > an external antenna. However, you haven't disclosed what's at the > other end of the link, how far away, how many walls, etc, so I can't > be sure this will work. > >>The transmitting signal I believe is quite strong, municipal,
>>but the problem lies in receive sensitivity. >
> Ok, so you're trying to connect to a municipal wireless network. How > far away? Line of sight? Anything in between you and the access > point? Can you install a directional antenna? > > Incidentally, what problem and who's receive sensitivity? The > municpal networks sensitivity or your proposed hardware? > >>Sorry if this has been covered somewhere, if you have the links to the
>>discussion? Thanks. >
> Suggestion: Please get organized and don't try to mix too many > questions together without a clear division. Also, models and numbers > are a good thing. > | ||||||||||||||||
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Posted by seaweedsl on December 27, 2008, 2:09 pm
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I'm not going to tell you my OS, radio make, etc. That is information that can conceivable could be used to identify me individually and I don't want that, thanks. LOL! Right. Let's see, uses Windows XP on a Dell inspiron and has a Netgear USB. That narrows it down to about 100,000 people ! Now if I just tune my wifi finder to look for the chip used in netgears and start circling the earth, I'll find this guy sooner or later. Once I do, boy, armed with which operating system he uses, I can really sock it to him ! This guy is pretty confident and testy in his misinformation ! Thus assuring that he will learn for himself. Best way to learn anyway. Though I have seen Jeff get past worst and still help somebody. Happy holidays Steve | ||||||||||||||||
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Posted by Jeff Liebermann on December 28, 2008, 12:41 am
Please log in for more thread options wrote:
>
>Go back and read the OP, cuz I don't think you did not understood what I >said, or more likely you began answering before you had read the entire >post. Both. I read it through twice before responding. I didn't understand what you were asking. Too many computer, too vague a description of your hardware, no clue what you were connecting with, few numbers. Actually, it made more sense reading it starting from the bottom and working up. However, I'm lazy and decided to reply in the order in which you presented your questions. If you want to avoid a repeat performance, try supplying: 1. What problem are you trying to solve? 2. What do you have to work with? (Hardware, software, equipment, network topology, topography, environmental issues, etc). 3. If troubleshooting, what have you done so far and what happened? Also, sorry for the delayed reply. Saturday degenerated into a work day for me. It's difficult to say no to the brats with their new Christmas toys. Once the toys were working, I was bribed into rewiring the home office. >I am getting a 40-66% signal strength using a wubber ducky pole antenna
>with a parabolic reflector behind it. I was asking what construction >factors, other than the ones I already know about (proper curvature and >placement of the wubber duckey pickup at the focal point) might maximize >the reflector efficiency. Thanks. The basics first. Signal strength is NOT the primary determination of download speed and connection reliability. SNR (Signal to noise ratio), which can also be represented by BER (bit error rate) and PER (packet error rate) is generally more important. For example, you can have a good solid connection, but if there's any interference along the path, you're going to see errors. With interference, such errors may not cause a drop is signal strength. The problem is that it's impossible to tune or aim the antenna by watching the SNR indication. This is where a high gain direction antenna is useful. Besides increasing the signal strength by providing gain in the desired direction, it also decreases the gain to the sides and back of the antenna, thus reducing the interference pickup. It doesn't do anything for interference at the other end of the link, but you don't have any control over that anyway. As for building your own reflector, the major issues (in order of importance) are: 1. Accurate parabolic curvature. You're trying to maintain at least +/- 1/10th of a wavelength accuracy. That's about 1.3cm which should be quite easy to achieve. 2. Feed illumination efficiency. This is the major problem with the hang-on reflector. Much of the TX RF goes in directions that don't hit the parabolic reflector. That RF is lost and cannot be recovered. See: <http://www.w1ghz.org/antbook/contents.htm>
in the section on feeds, illumination, spillover, etc at:
<http://www.w1ghz.org/antbook/chap4.pdf>
3. Different TX/RX gains. In transmit, feeding a dish with a
vertical collinear results in considerable illumination loss. That's not the case in receive, where everything that hits the dish will hit the collinear feed. 4. VSWR and matching. Placing a reflector near the antenna will change the characteristic impedance of the antenna. This may cause some additional TX loss. It won't be much, but if you're looking for optimum performance, this should be measured and optimized. 5. Width of the parabolic reflector. Most likely, your reflector is curved into a parabola only in one axis. It's flat in the other axis. The width of the reflector should be at least as wide as the antenna (ideally 1 wavelength or 12.5cm). Any wider will not help as the reflected signal does not go towards the other end of the link, but instead, goes towards up or down. For a clue, replace the collinear antenna with a light bulb (point source) and look at the reflected light pattern on the wall. That's very roughly how your RF is going to be distributed. It won't be a nice clean spot on the wall, but more like a vertical smear, with lots of wasted over spray to the sides coming directly from the lamp. Here's the Coleman lantern version: <http://802.11junk.com/jeffl/antennas/Misc/slides/lantern-reflector.html>
>Reflective material used (using alum foil
>now), Anything that reflects RF will work. Aluminum sheet or foil will work just fine. Most steel's will also work. Stainless steel salad bowl with USB dongle shoved down the pipe: <http://802.11junk.com/jeffl/antennas/Salad-Dish/index.html>
Incidentally, when I do the lamp test with the salad bowl, the result
is an annular ring on the wall. It's not a spot, but more like an out of focus ring. It's far from optimum, but better than the USB dongle alone. >size;
For single axis parabolics, about 1/2 wavelength (6.25cm) is the minimum height. I prefer 1 wavelength high (12.5cm). You don't want a deep dish (high f/D ratio) as reflections from opposite sides of the dish start to cancel each other. See: <http://www.freeantennas.com>
>what common mistakes are mostly made in homemade
>construction of these? None. Here's how it works. As long as the antenna gain is fairly low (i.e. <10dBi gain), you can be quite sloppy and still end up with a usable antenna. The basic design of stuffing a reflector behind a collinear is at best a kludge, but will still work better than the collinear by itself. The reflector can be flat or parabolic, and there will be perhaps 1-2dB differences in gain. For example, compare the dish and the flat plate reflectors based on the Hawkings USB bridge at: <http://802.11junk.com/jeffl/antennas/FullWavePlateReflector/>
7.7dBi for the dish.
<http://802.11junk.com/jeffl/antennas/HawkDish08/> 8.3dBi for the flat plate. Fairly close, methinks. When the gains go above about 10dBi, dimensions and construction techniques become rather critical. Small errors result in substantial changes in gain and pattern. Small goofs are less tolerated. What all this means is that you can be rather creative and sloppy with low gain reflector antennas, and still end up with a usable antenna. It also means that there's little you can do with the design or construction to make any dramatic improvements. Sorry. >It is already about as large as I want it to be
>for indoor use at about 2' by 1' The wubber duckey is about 7 inches >long. You probably won't believe me, but the gain of the rubber ducky (collinear) has no effect on the gain of the antenna. In fact, too much gain causes only a small part of the parabolic reflector to be illuminated, resulting in less effective aperture, and therefore less gain. A 7" rubber ducky will have about 2dBi gain resulting in perhaps a 60 degree beamwidth, which is sufficiently wide to illuminate almost any conceivable reflector. You're fine. You can calculate the maximum possible gain of a parabolic dish antenna: <http://en.wikipedia.org/wiki/Parabolic_antenna>
I can't calculate your 2ft x 1ft antenna without a clue as to how it's
built. >Second question is which brand/ model of usb dongle has the best
>transmit receive sensitivity (more important) for use with the same >reflector and my desktop computer. Sorry. I can't answer what's best. There are some high power USB devices: <http://www.ubnt.com/products/sr71usb.php> (250mw)
In my never humble opinion, there's no such thing as a good USB device. That's not the fault of the radio or chipset. It's the fault of the tiny antenna that's used in the typical USB device. There are some that have real antennas, or external antenna connectors that deserve some notice, but the ones with internal antennas are marginal at best. The generally crappy Windoze device drivers are also of little help. Note the external antenna connectors (MMCX): <http://www.ubnt.com/products/sr71usb.php>
>I cannot obviously use the pcmcia
>card with my desktop since I have to go about 10 feet to it and it is >designed for laptops. Actually, you can. Some PCMCIA cards have external antenna connectors. Instead of a reflector kludge, get a real dish antenna, with 19 or 24dBi gain, 10ft of LMR-240 or LMR-400, and approximately a 1ft LMR-100 or RG-316 pigtail adapter, and you can use the PCMCIA card. I've had good luck with Buffalo cards, but they're banned in the US thanks to patent litigation by CSIRO. >Now I recall that seattle wireless did some
>testing of these, which I have to revisit, but their tests were not very >comprehensive as I recall. Most of the numbers I saw were copied directly from the data sheets. There was some comparative field testing done, but that was for early 802.11b only cards. >I have no idea where the APs are, a visual survey of the area saw no
>tell tale antennas, one AP I am guessing is far away on a tower about 50 >feet high, probably about 3 miles away. You claimed that this was a municipal WLAN yet you can't find the antennas? Use your dish antenna, wave it around, and see where the signal is strongest. Do it from a place where you have a clear shot of the probable locations. There are maps of most municipal networks, but since you don't want to disclose identifying information, I can't help you find them. I'm not sure why you need total anonymity for a public wireless system, but that's your decision. >No line of sight, so I have no
>idea what is between us. I have at least 2-3 independent signals I can >connect to, so the relevant question is what can I use for the desktop >radio and a good usb radio is what comes to mind. I live in an apartment >complex, so I am stuck with an indoor reflector or antenna. Line of sight is important. You might be able to get a connection without line of sight, but you will probably not be able to maintain the connection. It will fade in and out as obstructions in the line of sight move reflections around. >Since I don't have a line of sight, I am guessing that a dish antenna
>will not work, since I have no reference point to point it to, nor do I >know what lies between me and the AP. Actually, I think a dish antenna would work best because it directs the signal where you most want it (and rejects junk coming from the sides). Still, it's difficult to predict without knowing what's along the path. >I am not going to buy fancy signal
>detecting equipment for this, it's a shoestring operation. > >The venetian blinds are oriented horizontally, and metal as I said >before, but their adjustment makes little to no diff in signal strength. Very strange. It should block a vertically polarized signal quite well. Sorry, but I don't have a guess as to what's happening. >I'm not going to tell you my OS, radio make, etc. That is information
>that can conceivable could be used to identify me individually and I >don't want that, thanks. You're more likely to be identified by sniffing your traffic and identifying your logins passwords and surfing habits. I'm always suspicious of people that want anonymity as I tend to assume they're trying to perpetrate a crime of some sorts. >I have doubts that there exists a usb dongle on
>the market that will match the receive sensitivity and transmit power of >the pcmcia card I am using. Agreed. Without knowing what you're using, it's difficult to tell. List of claimed rx sensitivities of various products: <http://802.11junk.com/jeffl/rx-sens/receiver%20sensitivity.htm>
Everyone lies, but that's ok because nobody listens.
>Most users report they are weaker.
It's mostly the differences between a relatively large diversity PCMCIA antenna system, and a tiny ceramic patch or PIFA antenna. The PCB antenna in the PCMCIA card might have about 2dBi gain. The tiny patch or PIFA are typically -2 to -4dBi. (6dB difference is 2 times the range). >If you
>have any concrete suggestions on how to maximize the efficiency of the >usb dongle, please state them. Don't use concrete. It will ruin the USB device warranty. >At this writing I don't know what else I can use with the desktop since
>I have to go about 10 feet to it and cannot install an outdoor antenna >in these apartments. Yep. That's because you haven't asked what to use. You've supplied a list of questions, some of which are relevant to the problem you're trying to solve, but most of which are just interesting diversions. Try asking what *TYPE* of antenna to use. I think a dish in the window is impractical for an apartment. However, panel antennas offer almost the same gain and are less obnoxious. The problem is that you don't know where the other end of the link is located. Therefore, it's possible that the optimum position of a window mounted panel antenna might be an inconvenient angle. If you can fabricate some kind of adjustable antenna positioner, it might be made to work. Look though the panels (and dish) antennas at: <http://www.fab-corp.com>
They also have 10ft coax lengths and pigtails.
You can use USB but I don't like them mostly because the drivers are marginal. I suggest an external USB or ethernet connected wireless bridge radio with an external antenna connector. I'm using various Linksys WRT54G mutations with DD-WRT firmware. It has a client mode that works well enough. It's not as convenient as a USB device, but works much better. There are also devices made for WISP (wireless ISP) service that might be suitable. See: <http://www.ubnt.com/products/>
under the various "Wireless ISP Solutions".
>Maybe a USB with a dish reflector behind it might
>be worth a try, all homemade. Have seen some cool ones made from an >umbrella. Naw, my salad bowl is more cool. However, WokFi is the current high fashion reflector: <http://en.wikipedia.org/wiki/WokFi>
<http://www.usbwifi.orconhosting.net.nz> Far too many Wi-Fi antennas: <http://www.dxzone.com/catalog/Antennas/WiFi/>
>You really did not answer my questions, but you did make me think about it
>more completely, so now I know what to research. Yep. That's the way I work. I explain how things work and where to look. You get to answer your own questions and solve your own problems. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 | ||||||||||||||||
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>factors are critical to home made construction of an aluminum foil
>u-shaped (approx) parabolic antenna?