9 ms·

This seems great for sending but how does it work for receiving? Or did you somehow do this on both ends?

by throwaway613834 9y ago

gonzo 9y ago
Most antennae are retro directive. Gain is gain.
- throwaway613834 9y ago
  I replied here: https://news.ycombinator.com/item?id=16012484 https://news.ycombinator.com/item?id=16012484
aylons 9y ago
It's not needed to do it in both ends. Naturally, improving both antennas is better than doing in only one, but every improvement in sending is completely equivalent in receiving for a system that uses the same antennas for both directions of communication. 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.
- throwaway613834 9y ago
  > It's not needed to do it in both ends. Naturally, improving both antennas is better than doing in only one, but every improvement in sending is completely equivalent in receiving for a system that uses the same antennas for both directions of communication. 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.
  - hunter2_ 9y ago
    Think of a parabolic dish on a microphone at a sporting event. The dish blocks noise and interference from the directions you don't want to listen to, and less noise and interference is as useful as if the sender had more power. Same result of better s/n either way. 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.
    - throwaway613834 9y ago
      > The dish blocks noise and interference from the directions you don't want to listen to 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.
  - TeMPOraL 9y ago
    The trick here (in this Wi-Fi example) is that the end you control is the end with parabolic antenna - if you can make it to collect enough energy for RX from an omnidirectional source, you can also make it send enough energy towards that source for its antenna to pick it up. 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.
    - aylons 9y ago
      No, as long as antennas and signal power is concerned, I stand by what I said: every improvement in transmission power has a equivalent improvement in receiving power. If you have a more specific doubt, please, feel free to ask.
      - throwaway613834 9y ago
        > If you have a more specific doubt, please, feel free to ask. 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.
- pjc50 9y ago
  I don't know why people are arguing so much with this when it's straight out of textbook antenna theory. Evidently it's very HN to work things out inaccurately from first principles. Edit: http://www.cv.nrao.edu/course/astr534/AntennaTheory.html 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."
  - aylons 9y ago
    Thanks for the reply. I'm on the move, in my phone, and has regretted on posting the comment as it is hard to elaborate further given the situation.
  - deleted 9y ago
    [deleted]
  - Obi_Juan_Kenobi 9y ago
    > Evidently it's very HN to work things out inaccurately from first principles. 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.
- Foivos 9y ago
  It has been ten years, since I had antenna classes in the uni, so I might be wrong, but I do not completely agree. 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.
adrusi 9y ago
I don't know much about radio, so your question had me stumped for a second, and the other replies didn't help me much. Here's my explanation: 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).

This seems great for sending but how does it work for receiving? Or did you somehow do this on both ends?

gonzo 9y ago

Most antennae are retro directive. Gain is gain.

throwaway613834 9y ago
I replied here: https://news.ycombinator.com/item?id=16012484 https://news.ycombinator.com/item?id=16012484

aylons 9y ago

It's not needed to do it in both ends. Naturally, improving both antennas is better than doing in only one, but every improvement in sending is completely equivalent in receiving for a system that uses the same antennas for both directions of communication. 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.

throwaway613834 9y ago
> It's not needed to do it in both ends. Naturally, improving both antennas is better than doing in only one, but every improvement in sending is completely equivalent in receiving for a system that uses the same antennas for both directions of communication. 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.
- hunter2_ 9y ago
  Think of a parabolic dish on a microphone at a sporting event. The dish blocks noise and interference from the directions you don't want to listen to, and less noise and interference is as useful as if the sender had more power. Same result of better s/n either way. 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.
  - throwaway613834 9y ago
    > The dish blocks noise and interference from the directions you don't want to listen to 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.
- TeMPOraL 9y ago
  The trick here (in this Wi-Fi example) is that the end you control is the end with parabolic antenna - if you can make it to collect enough energy for RX from an omnidirectional source, you can also make it send enough energy towards that source for its antenna to pick it up. 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.
  - aylons 9y ago
    No, as long as antennas and signal power is concerned, I stand by what I said: every improvement in transmission power has a equivalent improvement in receiving power. If you have a more specific doubt, please, feel free to ask.
    - throwaway613834 9y ago
      > If you have a more specific doubt, please, feel free to ask. 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.
pjc50 9y ago
I don't know why people are arguing so much with this when it's straight out of textbook antenna theory. Evidently it's very HN to work things out inaccurately from first principles. Edit: http://www.cv.nrao.edu/course/astr534/AntennaTheory.html 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."
- aylons 9y ago
  Thanks for the reply. I'm on the move, in my phone, and has regretted on posting the comment as it is hard to elaborate further given the situation.
- deleted 9y ago
  [deleted]
- Obi_Juan_Kenobi 9y ago
  > Evidently it's very HN to work things out inaccurately from first principles. 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.
Foivos 9y ago
It has been ten years, since I had antenna classes in the uni, so I might be wrong, but I do not completely agree. 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.

adrusi 9y ago

I don't know much about radio, so your question had me stumped for a second, and the other replies didn't help me much. Here's my explanation: 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).