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.
Edit: http://www.cv.nrao.edu/course/astr534/AntennaTheory.html
"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.
https://www.scientificamerican.com/article/first-practical-m...
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).
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.