Two questions-usb;antenna construction, please help?

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:

for clues.

Even a flat plate reflector will improve the signal. Try it. Piece of aluminum foil located behind the USB dongle.

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.

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?

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 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.

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.

What maker PCMCIA card? What model PCMCIA card? What laptop? What OS? What does this have to do with a USB antenna?

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)?

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?

Ummm... please fix the English. Which antenna? Coax or USB cable?

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?

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 wrote in news: snipped-for-privacy@4ax.com:

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.

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

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.

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: in the section on feeds, illumination, spillover, etc at:
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:

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:

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.

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:

None. Here's how it works. As long as the antenna gain is fairly low (i.e.

Ok thanks for your most recent reply, apologies if I was short tempered. Your latest reply is very good and comprehensive. I responded to some ot it and will research the rest. Unlike you I cannot devote my life's work to this, haha, but I will learn as time goes by. Like most stuff connected with computers, the more I learn the more I feel overwhelmed by it all, there is simply too much, too much change and too fast. Glad I am not in that field, cuz it must be hard. I am doing pretty good now, just need to get my desktop going and find a good usb

Jeff Liebermann wrote in news: snipped-for-privacy@4ax.com:

The card software only reports link quality and signal strength. I am now up to 66% on link quality and 60% on signal strength on one AP. Interesting the metal venetian blinds positioned downward are reflecting the signal to the focal point and increasing the signal strength. Since the signal improves when the reflector is raised a few inches, I am guessing this particular signal is coming form above and the blinds are reflecting it upwards towards the focal point, since it is down in height from the signal. This is all guesswork and I am just using the reporting software to determine the best position of the reflector/wubber ducky. Probably there is a software package that may give SNR or BER that works on winshit; if you know of a good one please let me know.

OK, now we are communicating thanks. By high gain directional antenna, r u referring to a dish type antenna, or which ones. I see alot of people using Yagi antennas here. Most are using yagi or small panel antennas but they are able to put them high on the roof, and I am stuck indoors. The little dish antennas I see advertised on the net, the desktop models don't look big enough to be high gain on first look. This homemade parabolic is doing pretty good, especially since it was kinda bent outta shape requiring reshaping when in storage, haha.

Ok thanks, good rule of thumb.

would not a dish antenna have the same problem, especially one small enough to be used indoors. Those umbrella home made antennas might be worth a try, but that is about as big as I want to go. Have you seen those with pix on the web, just using the reverse curvature of a common umbrella.

not sure I know what u mean by "vertical collinear" will look it up.

distance to wubber duckey from reflector is about 2inches.

Yes, ur right, parabola is horizontal only. Width of parabola is about

Good tip, thanks.

Sorry for explaining the laws of nature? :-) Ok, same with most things, the closer you get to perfection the hard it is to achieve.

Ok good, that gives me a good direction. Thanks.

Sorry if this is an ignorant question, but don't u also need an adapter to connect to the pins that usually insert into the laptop. Both my desktop and laptop are quite old, and the desktop does not have any place to insert a pcmcia card. What am I not knowing here? The card does have external antenna connectors; that is what I am using to connect the collinear antenna.

Problem is I am not certain. I THINK it is a transmission tower about 3 miles away and about 50 feet high. Most of the rooftop panel and yagis are pointed in that direction. I used to be able to connect with a very small reflector when I was about 1km away, but now I am about 3 miles away. I was not able to connect a few months ago and I think they boosted their setup, cuz now it is easy. But 3 miles? Hard to believe that it is that far away; also the signal seems to be disappearing at night, so maybe it is not municipal, It is not encrypted, that's all I really care about :-). I probably need to buy some type of detector, but as I recall they are quite expensive. I don't think the cheapie ones are going to help me find it. There are too many trees in the direction of the signal, so all I can see are branches and birds, mostly; if it is 3 miles away, like I am guessing, coule not see it even with my binoculars. I know it exists cuz when I was closer I used to connect. Maybe I saved the IP on my box, and will have to look it up and compare it to the one I have now.

well, maybe I just cannot see it? getting good stable connections with the laptop/pcmcia/reflector indoors, but not sure what I will get from usb. Probably if the usb is a good one like u mentioned above I will have no problem. I was debating whether or not to order a dish high gain antenna, and now, based on your comments, maybe a panel antenna, but I am doing pretty good with the homemade parabola reflector, so first is to try a good usb with either that or with some other homemade dish parabola. probably not gonna order one since they are hard to return.

Ok I have a lightbulb reflector that I can try with a good usb in the center (focal point). I have already done the light tests with it, so I have an idea of where the signal is focused. However it is not a true parabola but more concave (deep), but not that far off.

positioned now downward with curvature of blinds facing outside, I am getting the best reflection off them. positioned upward, the signal dies, haha. adjustable reflector venetian blinds, maybe I should try to market them, haha.

using encryption, all they will get is garbage. No I am not trying to do a crime, just don't want marketers pounding on my door and like to remain anonymous on the usenet, so when I have a flame war people don't hold grudges too long, ahhahahhaa. Last time I posted non anon, I got alot of junk mail connected with that and I need to start billing those people for all the extra trips I have to make to the trash, due to all their crap mail and also their junk phone calls.

very funny.

I thought I did, when I asked if a dish would be better? As I said most are using either yagi or panel near me, but they can put a 10 foot tower on their roofs to use them. I cannot.

Yeah that is what I have now since the reflector is fully adjustable. I am trying to avoid multiple trips to the stores when I buy a usb dongle and it doesn't work, haha. I will research that though; I think u already gave me some links I can use on that. Thanks. Also, I don't see without being an engineer, how the shape of a panel antenna or a yagi for that matter can beat the advantages of a parabola. The only question in my mind is if a dish antenna can be adequately directed to the signal. But since I am getting a pretty good signal with a half parabola, my guess it a dish with a usb dongle might work, if the signal is properly directed both in reference to the usb focal point and to the incoming signal. I will have to find some way of determining where exactly the AP antenna is located. Not sure how at this point.

Ok, thanks.

this is a shoestring op, doubt I am going t invst in a ethernet bridge radio. Last time I priced them I think they were around $150 or so. I tried one Buffalo radio, can't recall the model offhand, but it was not strong enough. This little pcmcia card is amazingly good.

Ok, this reply was more than even I asked for. Thanks alot.

Once again, Jeff proves what a gentleman he is.

On Sun, 28 Dec 2008 12:28:29 -0800 (PST), seaweedsl wrote in :

Indeed!

snip!

You can make a DIY setup like below, or purchase adapters like at bottom links. Get netstumbler for testing.