The hotspot was some kind of public service provided by the Romanian town as it's name suggested. The ip WhoIs also confirmed that it was a Romanian one.
Every now and then the connection would have had slowed down and I would do some "Voodoo magic" on the aluminum foil to fix it(Not sure if it was me though, it seemed like if I move the dish slightly or fix a bump in the foil the connection would improve).
This was probably like 7-8 years ago and I was able to get something close to 6-7Mbps as far as I remember.
It gets even better if you drill a hole in the center and stick an antenna vertically in there. Now you've got a wi-fi antenna with all the advantages of a satellite dish! The Chinese call it wok-fi.
And Cisco Press do some good books on the basics of WiFi network design.
So, if a new antenna in client side improves signal reception by 3dB, it also improves transmitted power by 3dB. If you used the same antenna on the other side, the 3dB would be added again in both reception and transmission, for a total gain of 6dB each direction.
"An antenna can be treated either as a receiving device, gathering the incoming radiation field and conducting electrical signals to the output terminals, or as a transmitting system, launching electromagnetic waves outward. These two cases are equivalent because of time reversibility: the solutions of Maxwell's equations are valid when time is reversed."
I find this quite common among people that consider themselves technically minded. One of the key indicators I have for truly 'smart' people is an inclination toward curiosity with new things, and perhaps a degree of humility.
Does this actually make sense to you? Gain is a factor; it needs to be multiplied by something. Here's the obvious thought-experiment: consider an (ideal) parabolic mirror in (a vacuum). Put a lightbulb (infinitely tiny) at the focus. Light will come out parallel and will be just as strong no matter how far away the receiver is. i.e. the distance will be irrelevant when the sender is at the focus. Now try reversing their roles, with the lightbulb far away and the receiver at the focus. How strong is the received signal at the focus? You're claiming it won't matter how far away the sender is from the focus, which makes no sense.
> You're claiming it won't matter how far away the sender is from the focus, which makes no sense.
You are correct in that it makes no sense, but the claim was "every improvement in sending is completely equivalent in receiving for a system that uses the same antennas for both directions", key word improvement. While this is not entirely correct, this approximation (that antenna improvement works both ways equally) is pretty close to reality in practical far field applications.
I don't get why you put "necessarily". You do not, period.
> [...snip...] but the claim was "every improvement in sending is completely equivalent in receiving for a system that uses the same antennas for both directions", key word improvement.
Yes, the claim is wrong:
1. With the sender at the focus and the receiver farther away, the mirror reduces the loss (due to distance, since everything else is assumed ideal as you already acknowledged) to ZERO. You literally cannot do better than reducing your loss to zero.
2. With the receiver at the focus and the sender farther away, the mirror DOES NOT even remotely reduce the loss due to the distance to zero. Loss is still ~1/r^2. Because the mirror only gets so much of the omnidirectional light. This should be very obvious.
I don't care how you slice and dice this, and I'm tired of arguing something this obvious, so I won't keep commenting. 1 is not equal to 1/r^2.
You're arguing a scenario that is impossible both practically and theoretically and then calling others pedants for pointing out the fundamental flaws in your thought experiment. You're literally arguing against the textbook and then asserting that your thought experiment is close enough to make your point. It might be time for you to stop assuming that everyone else is an idiot and entertain the notion that you might actually be wrong.
But you're right that "every improvement in sending is completely equivalent in receiving for a system that uses the same antennas for both directions of communication" is wrong; there are different ways of improving TX and RX, even though some overlap a bit, to some extent.
Unless by "feel free to ask" you mean "I don't plan to answer", this doesn't really seem like a sincere suggestion. I already did this and you didn't answer.
Have you studied physics and antenna theory?
No it won't, it's diffraction-limited. The best you can theoretically do is an https://en.wikipedia.org/wiki/Airy_disk
You cannot construct, with any arrangement of mirrors or lasers, a beam that does not diverge.
The fact that you can't have perfectly collimated beams and must make do with antenna pattern "lobes" is actually important here.
Or a TV satellite dish. If you were correct, you could rip off the dish and point the antenna forwards instead of backwards, and still watch TV. Not gonna happen.
You shouldn't need to talk about noise or interference for the argument to make sense. Just imagine there isn't any. The argument yields absurd results either way: the power certainly does depend on how far the sender is from the focus.
Gain is the same in both ends, but my concern about receiving is that gain is applied to everything. This includes interference and noise. So at the receiving end if the SINR is already bad, the antenna gain is not going to help much. This is why you apply the "Low Noise Amplifier" right after the antenna. To make sure that an already bad SINR will not get even worse in the rest of the receiving stages.
Some celestial bodies like the moons of Jupiter, are too dim for us to see, because the amount of light that hits our pupils is too small for our retina to react to. But the light from the moons isn't pointed directly at our pupils, it goes in all directions. If the area of our pupils were twice as large as it is, we would be getting twice as much light from Jupiter's moons — and everything else (except a laser pointed at your eye, please don't point lasers at people's eyes). Telescopes work by being a HUGE pupil, collecting all the light from a wide area and pointing it all right at our pupils (that's not the only thing they do, but it's an important part).
An antenna is like a pupil, and a satellite dish, or this piece of aluminum foil, are like a telescope. Some of the signal from your laptop in the bedroom goes and hits the antenna with a weak signal. A lot more of the signal misses the antenna and hits the foil, and then gets reflected where some more hits the antenna (since the foil was curved, more of the signal hits the antenna on the rebound than on the first pass).
Then you follow the assembly instructions, which are indeed a bit minimal; The six "bumps" (called "tabs" in the instruction) sticking out the "Windsurfer" part are probably supposed to stick into the six cut-lines of the rounded rectangle piece you cut out from the bottom of the sheet.
This will make the "Windsurfer" part a particular curved shape. I suppose this is the "reflector", so you probably should glue the aluminium foil only to this part.
Then there's the two crosses on the "Windsurfer" part, which you also cut out with a sharp knife, and seem to me to be just the right kind of holes to pierce the whole thing on a wifi-antenna. Get the picture?
Some kind of photo of the finished end-result would have been nice indeed :)
Disclaimer: I know almost nothing about radio signals or antennas etc, the above is just my interpretation of the instructions on the site.
What he's likely do is shielding the wifi receiver from co-channel interference, which is likely reducing the noise floor at the AP - which is giving him effectively more range, because now the AP can hear stations that are further away with greater ease.
I don't think this is giving expanded tx coverage lobes as his diagram indicates, its likely a function of lowering the noise floor that gives the extra coverage.
It won't be a satellite dish as the comment thread on the page mentions, though, which is both a passive reflector and a focusing device, whose curvature requires at least some level of precision to be of any help.
For something much more helpful, see http://ham-radio.com/k6sti/wifiyagi.htm
It may very well be working in more than one mode - but I strongly suspect its a far better shield, than it is a forward power reflector. It also may strongly effect the VSWR of the existing dipoles used here.
But to be fair, it's a wild guess. It's a semi-flat piece of foil placed at an angle, at a random distance from 3 individual antennas. That's why I linked to the nice and simple, easy-to-calculate yagi-uda for if you want to hack with antenna gain.
No disagreement that the yagi thing you pointed out would work better.
That said, this is a MIMO router, so that may change the modulus on the multipath problem.
A regular home Wi-Fi network is already a complex multi-path system, as the primary propagation mode is reflections from walls and ceilings, leading to plenty of self-interference with many hot- and cold-spots from constructive and destructive inteference. We are at most introducing a few stronger reflections in an already extremely reflection-heavy environment. The big question is whether it does any good, either through attenuation or gain.
As for MIMO, I must admit to not knowing much about it—I know it utilizes spacial separation to increase bandwidth, but I do not know much of its actual implementation, and thereby weaknesses.
Might put a crimp on your cell phone reception ...
https://www.lessemf.com/paint.html (Warning: this site gets a little silly)
You might need to replace a couple of older pieces of equipment, but it's a hell of a lot cheaper than turning your house into a Faraday cage.
When messing with antennas, things like distance needs to be thoroughly calculated. Foil can help in many ways, but it can also make things worse—antenna calculations are tricky.
Especially at high frequencies. One of the first things I did when I got access to a computer as a kid was to write an antenna calculation program for Yagi antennae.
Impressive gain by the way, a factor of 8 (almost 9 dB) from that super simple mod.
In short, I'm looking for logic to repeat this for my router's dipole antenna and possibly with custom wires (not #14 or paperclips of unknown thickness mentioned there)
Otherwise, there's plenty of 3-element Yagi-Uda calculators online where you can stuff in various amounts of parameters and get the unknowns—the author used fancy antenna simulation software, but you don't need that.
A few links:
Of course you'd have to do the same thing at the receiver.
Anyone more knowledgeable able to chime-in on the effect of creases here? I couldn’t find any mention of it in the article...
If you can keep the size of the largest crease/feature/defect in your foil smaller than this, you should be okay.
So something like:
Source ----------------------------------- Dest
By the time the reflection gets back to the transmission line, you have a phase offset of half a wavelength relative to original signal on the transmission line. If you add two signals that are half a wavelength apart, they combine destructively (cancel each other out). So the quarter wave stub acts like a very basic filter, and you actually won't see much of your signal at "Dest" when your transmission line has a quarter-wave stub like this.
Microwave engineers use all sorts of tricks involving transmission line segments that are a quarter wavelength long. So when you're trying to build an antenna (e.g. out of foil, or if you're adding metal support structures to a large antenna), it's helpful to use the heuristic: "if you need to add features that are not part of the original design, try to keep them smaller than a quarter wavelength."
blackguardx is right that restricting the maximum feature size to 1/10 of the wavelength is probably a better rule of thumb if you want good performance. If you can get it down to say, 1/2 of a quarter wavelength (1/8 wavelength), there's a reasonable chance it'll still work.
Would love to dig into the science behind this a bit more — I don't really know where to start — i.e. why you're dividing by four.
So as not to waste your time, is there a named phenomenon that you can link me to to learn more about this?
I would say that you want to be less than 1/10 of the wavelength to minimize the effect though.
That has the look of a rule of thumb, which as a civil engineer that ended up in IT, sounds a bit familiar.
How is the author drawing those diagrams? Can I map my room with the strength of wifi signals at different points?
I want to do these small hacks but also want to see the change validated in some way. Any pointers will be appreciated.
It also should work equally well when receiving and transmitting, whereas an amplifier would work for only one direction (so you'd need two, one to output more power, another to amplify the received signal).
I did some pretty interesting stuff with 19 element Yagi's and very low power transmitters.
I use one at my Dad's house (next door to mine) so that I can access my wifi. Our houses are brick, and in spite of that, the extender I got does a pretty good job. I've tried various extenders in the past few years, and they were all pretty flaky, but the latest generation of extenders seems to perform much better than older ones.
I'm using the Wirecutter's current favorite, the TP-Link RE450. Having said that, the RE450 was recently found to be spamming NTP servers with an excessive amount of requests.
Good usb dongles are:
1. Alfa AWUS036NHA – $28.97
2. TP-LINK TP-WN722N OR TP-WN722NC $15.99
have "your" wifi on a separate channel, you have your own subnet, firewalled (nat) from your neighbor's net.
It also lets you put your devices on their own subnet/NAT, which is nice from a security perspective (I've do this at home quite a lot - re-purposed router connects the main network on 2.4GHz and treats it as a WAN, then provides its own connections on 5GHz).
The red circle in his first image will like be much more distorted in practice by the bomb shelter, meaning his home WiFi will have a lot of trouble reaching whats behind the shelter (i.e. the bathroom and the Mr Bedroom in particular). Basically he got a pretty horrible spot for his router. Study/bedroom3 would have been substantial better.
Large public buildings maybe still need shelters by law.
It could barely sustain a connection, never mind actually doing anything. So I cut up the neck of a bottle, covered with aluminium foil, and even added a little reciever at the focus point of the dish.
Signal bars went to a solid usable III.
In transmit , the reflector provides focusing, which puts more power in less of the volume. In receive, the increased aperture allows the antenna to capture a greater area of the incoming wave giving more receive power. The effects are equal and usually just thought of as"gain" which is reciprocal for transmit and receive.
It worked, but other directions are difficult. I also had success by changing the channel with less interference in my router settings.
https://eero.com or the UniFi Mesh
But for home use multiple AP's with powerline to connect them is actualy a simpler solution than mesh as using wifi for the DS (distribution system ) is always going to be slower than a wired.
if not, why aren't there cheap and effective such designs on alibaba - why have to DIY?
There are tons of products for sale. You can get a replacement antenna that is a directional dish for example, instead of the typical omnidirectional dipole (stick).
AFAIK, many countries limit the EIRP, which increases with the antenna gain.
It's more complicated for 2.4 GHz point-to-point. At 1 watt transmitter power you are allowed a 6 dBi antenna. But for every 1 dBi you reduce transmitter power, you are allowed an additional 3 dBI of antenna gain to a maximum of 30 dBi antenna gain at 160 mW transmitter power.
5 GHz has even more complicated rules, I believe.
how does that work? isn't all wifi traffic encrypted by something between devices and AP?
(I skimmed your link and did a find for encry on it but saw nothing.)
I have a basement with thick walls.
I was staring at a blank page with a single image for over 10 seconds before the article text loaded. No loading indicator or anything.
How else would you add live comments without JS? This page is effectively a big chatroom. You can write at the bottom of the page and the website fetches the new messages async.
Don't tell me you would have a big http refresh every 5 seconds to load in the new chat messages, that's even worst than using JS.
Well, the website is called jiffchat.com and is a collection of chatrooms.
I hate sites that require JS and are not viewable on archive.is or Wayback Machine.