5 ms·

If you don't understand logarithmic scales, maybe you shouldn't be specing parts for a network-connected gizmos?

by sannee 8y ago

lovelearning 8y ago
Out of the first 10 or so results for "wifi routers" on Amazon, atleast half of them mention antenna dBi values. What is Joe Buyer supposed to infer if one router says 5 dBi and another says 6 dBi? Is it 5 times more powerful? Is it 10 times more powerful? I've read through the Wikipedia article on antenna gain and I still can't tell for sure. Negative values are even more confusing for people. Ultimately, I think the loss is entirely that of router manufacturers because their preferred units don't help potential buyers judge which is better and by how much. They can use dBi for research and development, but customers really need something more user-friendly. It's a matter of usability.
- gh02t 8y ago
  To answer your question: The gain in dBi is 10 * log10(linear gain), so the linear gain is 10^((gain in dBi) / 10). So 5 dBi is a gain of 3.16, and 6 dBi is 3.98. Log rules mean you can just subtract, so the difference is 1 dBi, meaning a 6 dBi antenna is 1.25 times more powerful than 5 dBi. I'm not sure what alternative units you could use, because log units are more natural. Joe consumer can understand "6 dBi is 1dBi better than 5 dBi," he doesn't need to know the details any more than he needs to know exactly how much faster his car will go with 10 extra horsepower. It's the relative comparison that matters (more horsepower == more speed) and using dBi makes those relative comparisons simpler.
- squarefoot 8y ago
  They use dBi (dB gain related to an isotropic radiator) on commercial devices because it's more accurate by referring to a theoretical antenna having gain of exactly 0. Antennas can't amplify signals; to have some gain in one direction they have to lose it in others, so that the isotropic antenna has a radiation pattern of a perfect sphere and its gain is 0, a dipole which loses gain in directions parallel to its axis shows some gain perpendicularly, a patch antenna uses a reflector behind it so that they get more gain in one direction, and a Yagi one also uses directors to narrow that direction even more, thus getting more gain in that direction. The downside to using dBi is that being a number related to a theoretical antenna it is higher and welcomed by advertisers: if you take out your router external antenna having a gain of say 2dBi to swap with a higher one that gains 9dBi, you don't get a gain of 9dB, but vendors still can write 9dBi on its box. For home devices, usually smaller dipoles or longer collinears are used because they are the best choice in a scenario where the user needs to cover his/her house and not the neighbors (just keep the antennas pointed up or down, not sideways). There are many other kinds such as slotted, grid, helical, sector, patch, Yagi, etc. each one with its best use case. Building them is also fun and cheap.

If you don't understand logarithmic scales, maybe you shouldn't be specing parts for a network-connected gizmos?

by sannee 8y ago

If you don't understand logarithmic scales, maybe you shouldn't be specing parts for a network-connected gizmos?

Out of the first 10 or so results for "wifi routers" on Amazon, atleast half of them mention antenna dBi values. What is Joe Buyer supposed to infer if one router says 5 dBi and another says 6 dBi? Is it 5 times more powerful? Is it 10 times more powerful? I've read through the Wikipedia article on antenna gain and I still can't tell for sure. Negative values are even more confusing for people. Ultimately, I think the loss is entirely that of router manufacturers because their preferred units don't help potential buyers judge which is better and by how much. They can use dBi for research and development, but customers really need something more user-friendly. It's a matter of usability.

gh02t 8y ago
To answer your question: The gain in dBi is 10 * log10(linear gain), so the linear gain is 10^((gain in dBi) / 10). So 5 dBi is a gain of 3.16, and 6 dBi is 3.98. Log rules mean you can just subtract, so the difference is 1 dBi, meaning a 6 dBi antenna is 1.25 times more powerful than 5 dBi. I'm not sure what alternative units you could use, because log units are more natural. Joe consumer can understand "6 dBi is 1dBi better than 5 dBi," he doesn't need to know the details any more than he needs to know exactly how much faster his car will go with 10 extra horsepower. It's the relative comparison that matters (more horsepower == more speed) and using dBi makes those relative comparisons simpler.
squarefoot 8y ago
They use dBi (dB gain related to an isotropic radiator) on commercial devices because it's more accurate by referring to a theoretical antenna having gain of exactly 0. Antennas can't amplify signals; to have some gain in one direction they have to lose it in others, so that the isotropic antenna has a radiation pattern of a perfect sphere and its gain is 0, a dipole which loses gain in directions parallel to its axis shows some gain perpendicularly, a patch antenna uses a reflector behind it so that they get more gain in one direction, and a Yagi one also uses directors to narrow that direction even more, thus getting more gain in that direction. The downside to using dBi is that being a number related to a theoretical antenna it is higher and welcomed by advertisers: if you take out your router external antenna having a gain of say 2dBi to swap with a higher one that gains 9dBi, you don't get a gain of 9dB, but vendors still can write 9dBi on its box. For home devices, usually smaller dipoles or longer collinears are used because they are the best choice in a scenario where the user needs to cover his/her house and not the neighbors (just keep the antennas pointed up or down, not sideways). There are many other kinds such as slotted, grid, helical, sector, patch, Yagi, etc. each one with its best use case. Building them is also fun and cheap.