A non-expert doesn't care about antenna gain - he just wants his wireless connection to work (or his radio signal to be clear). When he starts researching antenna gains he delves into the hobbyist scene. I know that hobbyists are not experts but understanding how dB work is simple enough after you understand the practical rules:
1. A difference of 3 in dB means times 2, a difference of 10 means times 10.
2. Because dB are in logarithmic scale adding dB multiplies the effect.
3. Negative numbers work the same but with loss instead of gain.
Thus a 3 dB gain antenna will double your signal strength while a 9 dB antenna will make it (9=3+3+3) 8 times stronger (8=2x2x2). Another example: 23 dB is a 200 times gain (23=10+10+3).
>1. A difference of 3 in dB means times 2, a difference of 10 means times 10.
How can this be right? Aren't you kind of fudging it a little?
Here's my train of thought:
First I was thinking "What the hell is going on with your math? There's no clear factor to turn base 2 into base 10 what the hell. How can what you say be true? How does this work?"
My next thought (based on your incorrect statement) was, oh, they didn't choose base 2: they chose every 3 to be another factor of 2 - so let's see why that works, why +10 is the same as * 10 if every +3 is * 2. Well, you can get to 10 by going 3 + 3 + 3 + 1 and you can also get 10 by going 2 * 2 * 2 * (1.25) = 10.
Okay, so if every +3 converts to * 2 then why exactly does the last term, +1 convert to * 1.25?
I thought, and thought about it. I couldn't make it work, based on your rules. So I checked. And the answer is it doesn't: 2^(1/3) isn't 1.25 as we would expect, it's 1.2599. That might seem "close enough" but I think it's not exactly how you say and your statements are misleading.
Thus 23 dB isn't 200 times stronger as you state (23 = 10 + 10 + 3), it's only approximately 200 times stronger. 200x stronger is 23.0103 dB, and 23 dB is 199.52 times stronger. [1]
While it's useful, and the error is pretty small, it doesn't help for those of us used to thinking in terms of bitfields or something that converts quite exactly.
It's definitely a very useful mental estimation trick though!
[1] which I checked with an online calculator here - https://www.rapidtables.com/electric/decibel.html (first I entered a level of 200 and clicked the top "convert" button, then I entered a dB of 23 and clicked the second "convert" button)
Well these are practical rules that are more or less used by people working with dBs. These people are usually don't think in term of bitfields - when you have a 43 dB gain antenna you don't care if it amplifies 20 000 times or 19 952 :) Also it's a nice way to show-off to people that do not know this rule!
In any case, I never said that you get 100% accurate results; if you want accuracy then you should use your calculator (or your logarithmic ruler); but why use a calculator when you roughly want to understand how much a 15 dB gain would be?
Finally, there's a nice way to find out how much 1 dB is with the mentioned rule: Notice that 1 = 10-3-3-3 thus it's 10/2/2/2 = 1.25 so 1 dB is approximately 1.25 gain as you said :)
Yeah, it's not exact, but in RF/microwave work you often get on order of a dB of loss through the cable or connectors anyway. Plus signal sources and spectrum analyzers are not spec'ed to be as accurate as you might expect. So you end up with error bars in your head.
The logarithmic scale is appropriate to represent things that behaves in a logarithmic way. A linear scale would be hard to manage since you'd often end up with extremely small and extremely large values next to each other which would be painful to represent and think about. Take a typical filter response graph for instance: https://iowegian.com/wp-content/uploads/2015/04/rcfreq.gif
Try graphing that with a linear scale, there won't be a lot to see I wager. It's true that it does take a little time to familiarize oneself with non-linear units at first (especially if one wants to add or subtract them for instance) but they have their uses. For measuring a signal they're clearly appropriate.
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.
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.
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.
There are too many things to be an expert in these days to be an expert in all of them.
Understanding log scales is easy. Understanding how a decibel rating on an antenna relates to your network-connected lawn ornament's expected range in meters is a whole different kettle of worms, and bigger numbers are better when they're range but not when they're cost.
