Here is the template for the antenna I will construct from this template:
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Here are some photo examples:
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I will do much better with the construction-more precise in curve and focal point than the examples shown. Can't remember the dBi, but author claims this is a high gain antenna when made correctly.
Antenna will be used indoors only from an apartment, pointed at the window:
a) As far as reception power goes, will it improve or worsen reception to make the reflector larger beyond the dimensions of the the whip antenna? I was thinking of doubling the size in both dimensions which will make it significantly larger than the antenna. Instead of 1' by 1' approx 2' by 2'. Directions call for it to be equally tall as it is wide, do they have that right?
b) what else can be done simply to improve the receive portion of the signal in construction of this antenna.
c) I will use a 10 foot usb extension to my radio, does that cut the power of the tranceiver at all? Does the placement of the usb extension wire factor into receive sensitivity?
d) the antenna screws into the top of the little usb radio. The usb radio is about 2-3 inches in height itself. Does the radio body take part in any signal pickup or interference thereof?
e) where exactly is the pickup inside most of these antennas as shown in the pictures?
But now I prefer the Windsurfer from the same site.
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on photo paper for thick stock, with aluminum foil glued to the sail, provides a substantial boost in signal. Leave the "tabs" longer than indicated on the drawing, for easier assembly.
No. Primarily because they have been from different eras, and I've used different tools to measure the gain, as well as different routers and laptops.
I have used three of the reflector patterns from freeantenas.com . The windsurfer is the prettiest of the them, and shows good gain in Netstumbler, as well as a noticeable improvement in drop out rate on some inferior WiFi clients.
My current laptop is so much better than the old equipment that I probably don't need the reflector for it.
NetStumbler, if I recall correctly, has some maximums, so this graph probably shows a max verses the non-reflector, and not the true difference.
Not really. If you double the aperture size of the antenna, you'll get a theoretical increase in gain of 3dB. However, that doesn't include reflector efficiency, cancellation due to multiple paths (more on this later), feed overspray, etc. Also, antennas of this type tend to have different gains in TX as in RX (due to overspray). To get them equal, matching the feed pattern to the dish f/D (focal length to diameter) ratio is important. With an uncontrolled feed (i.e. omni rubber ducky antenna), much of the RF radiated by the feed does NOT hit the dish, and therefore is not sent out the window in the desired direction. If I arbitrarily assume that half the radiation from the omni does not hit the dish, the TX gain is automatically 3dB less in TX than in RX, where all the RF that hits the dish ends up somewhere on the omni antenna.
Start here:
and especially read the section on feed design and overspray (spillover) and matching the feed to the dish.
There's no technical requirement that the antenna be symmetrical. It's just easier to calculate that way. The gain is mostly determined by the frontal area (aperture size), which can be rather asymmetrical. However, make an effort to make the antenna longer than the omni antenna feed or RF off the end of the omni will miss the reflector.
Simplify it. There's really no need for a parabola. A flat plate reflector or two flat plates forming a corner reflector will work almost as well. See:
This is a comparison of a parabolic dish, as found on a Hawking something client radio, and an equivalent sized flat plate reflector.
7.7 for the dish, and 8.3 for the flat plate. A corner reflector will do better, but I'm too lazy to model one.
What you must realize is that as antennas get bigger, and gains increase, the dimensions and limitations become more critical. The reason the aforementioned antennas, and most of the salad bowl and kitchen accessories reflectors work is that all of these offer an improvement over a simple rubber ducky antenna at low gains. However, to use the same techniques for higher gain antennas just isn't going to work. A slight construction or dimension error, and it just won't work as well as expected.
Nope. The xmit power at the end of a USB cable will be exactly the same as the xmit power when the USB dongle is plugged directly into the computah. The only loss is in the +5V DC power to the device, which is adequate for most such dongles. On the other foot, 10ft of coaxial cable has a rather high loss at 2.4GHz and should be avoided if possible.
Nothing you do to the antenna affects the "receive sensitivity". That's measured at the receiver input, without an antenna.
The gain of the antenna is affected by the placement of the USB cable. It's best to run it through the center of the dish, where it doesn't block the signal in any way.
A little. The radio itself is not very well shielded and can radiate quite a bit of RF without any antenna. Most of the RF comes out of your unspecified model USB radio, but there is a little leakage from the case. If you mount the USB radio in the aperture of the dish or reflector, it's going to block some of the signal. Same with the cable. Look at it from the optical point of view and pretend your working with light instead of RF.
I can't tell because you haven't bothered to supply what device you're using. Usually, it's a tiny ceramic antenna at the very end of the USB dongle, which will form a rough hemispherical pattern.
Now, I have a question. A few months ago, you posted this photo:
and engaged in an irritating and pointless dialog over its purpose, despite several people having successfully guessed the manufacturer and its function. Wanna explain what that was all about?
Jeff Liebermann wrote in news: snipped-for-privacy@4ax.com:
You are a thorough bloke aren't ya? Hehe, I like you Jeff, so as one sometime irritator to another I will answer.
I was getting open wifi connections from several of those pictured devices that could not seemingly be found to be emanating from any other AP. While I knew ahead of the post that these devices are *supposedly* fiber optic hardware of some kind, after alot of exploring I could find no other probable nearby source of the APs I was connecting to. Neither antennas, nor any other conceivable source of the signal. The signals were also strongest when pointed directy at those devices, and dropped off when pointed away. I concluded, rightly or wrongly that the signals were coming from the pictured devices, located in areas that suggested some type of mesh network. I was attempting, with some success, to draw out replies from a group that is usually either ignorant or anal- retentive in trying to answer questions from anyone who is not (stupidly) paying $40 a month for a simple wifi connection. In fact this group would be rather worthless if it was not for the occasional good answers coming from you. Since I am no electronic guru like you, it was impossible for me to determine if the wires leading away from those devices were power cables or not and cannot answer your question about that. In fact RF wifi communication is so bizarre I frequently wonder if etheral spirits are guiding it's weird permutations. I have no desire to enroll back in college to attempt to gather the math necessary to get to your level of expertise in these matters, which I what I would have to do to fully understand WHAT THE HELL IS HAPPENING??!! :-) Have a nice day, Jeff.
I try to be thorough. Sometimes, I'm even correct.
That's not as far fetched as you might expect. About 10 years ago, a consortium of companies that normally hate each others guts, got together and proposed an LMDS system, where the 30GHz radios were mounted on telephone poles. You would be expected to buy cordless phones (similar to cell phones but at 15 times the highest frequency), and use them instead of wired POTS phones. In addition, CATV video was to be provided via LMDS, as would internet access. In effect, it eliminated the "Last 30ft" drop between the pole and the house. There were plenty of things wrong with this idea, not the least of which was AT&T's proposed 128Kbits/sec data rate for internet. However, the rationalizations behind this abomination are still in place. There's nothing to prevent someone from doing the same thing at Wi-Fi frequencies, but I doubt it. If deployed, it certainly would not be packaged in cable splice housings.
Locally, PG&E (the local power utility) is installing Smart Meters on gas and power boxes that use 900Mhz spread spectrum. There are 2.4GHz models, but they're both frequency hopping, not DSSS, so you won't see them with a Wi-Fi sniffer. You need a spectrum analyzer. The PG&E pole mounted DCU radios used to interrogate the meters are rather obvious and festooned with antennas.
Last resort: Climb the pole and look inside the box.
Hint: You get better answers when you thank those doing your research rather than insulting them.
All you had to do was mention your suspicions and ask how you could verify that they're belching RF. I do that all the time tracking down sources of interference. It takes the biggest dish I can carry (24dBi), and small SHIELDED radio attached to the dish, and whatever spectrum analyzer software happens to be installed on my laptop this week.
RF is Magic.
Forget the math and take some physics. You'll get enough math as you go along.
The phone is ringing endlessly, it's going to be very hot today, there's a huge crane outside my window dropping several 150ft fir trees, and I just bought some test equipment that blew up after several hours of operation. I'm not having a nice day.
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