A lesson in wireless engineering from the Raspberry Pi
embedded-computing.com
embedded-computing.com
http://www.proant.se/en/news/2017/03/01/raspberry-pi-zero-w-...
The simplest solvers for Antennas do a great job on dipoles or other simple structures, and less well on antennae like the one on the Pi. I found it humorous that a well used tool was called 'Microwave office'[1].
I tried to do some genetic antenna design using a plotter, some conductive ink, and a simple S meter but it is really difficult to reliably connect the plotted antenna to the test fixture.
What I have learned, which matches the author, is that there is a lot of subtlety in antenna design that is not obvious by the traces they use on FR-4 or other substrates. That rabbit hole goes pretty far down.
[1] http://www.awrcorp.com/products/ni-awr-design-environment/mi...
For example if you need a big PCB, cheaper to make a big 2- or 4-layer PCB and put a module on it than to make your entire PCB 10 layers so you can break out a tiny BGA.
I've seen several commercial products that are just Pi-in-a-box, for small runs it's fine.
I setup my pi without keyboard and monitor (ssh only), and used this guide to set it up itself: https://www.losant.com/blog/getting-started-with-the-raspber...
Here's the list of my hardware: https://www.canakit.com/raspberry-pi-zero-wireless.html https://www.canakit.com/raspberry-pi-camera-v2-8mp.html
One is bolted to a utility pole outdoors, 200+ft away from the nearest WiFi access point through several walls. It's not a high link speed, but it works with nothing but that little triangle PCB trace cutout for the antenna.
It has been out for a few years now but is never in stock anywhere for the advertised price of $5 ,it's sometimes available bundled with loads of crap you dont need for 10x this price, also you cant buy a qty of more than one anywhere.
If they've stuffed up the pricing and trying to reduce their exposure I am pretty sure a lot of people would be happy paying $10 instead.
I'm pretty sure there are more Tesla Model 3's being produced than Raspberry Pi Zeros :-)
http://linuxgizmos.com/worlds-smallest-quad-core-sbc-starts-...
Small rx, small tx: low frequencies are better (lower loss).
Small rx, parabolic dish tx (or reversed): frequency does not matter.
Parabolic tx and rx: higher is better.
Small here means something like resonant dipole, so the antenna has to be physically bigger the lower the frequency.
For the case of a parabolic dish, we hold the diameter constant vs. frequency.
Anyway for phones lower bands are better as long as the antenna fits.
But... then you start encountering higher path loss. To make up for that, you need to increase transmitter power (whether by increasing actual power, or by using higher gain antennas, etc) or by adding redundancy to the data stream (e.g. FEC). The added redundancy chips away at your bit rate, but corrects errors.
In practice, whether you get a better net transfer speed on a narrow lower-frequency band or a wider higher-frequency band is going to depend on a lot of factors. Sometimes it pans out, sometimes not.
[1]: https://www.raspberrypi.org/magpi/pi-zero-w-wireless-antenna...
Comsol? You can use it for all physics.
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.
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.
Even if you don't understand log scales and you're trying to decide what to buy it's literally just bigger numbers = better.
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.
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.
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).
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)
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 :)
10^(3/10) = 1.995262315
-4 is not so good. -1 is very good.