
A lesson in wireless engineering from the Raspberry Pi - sohkamyung
http://www.embedded-computing.com/iot/a-lesson-in-wireless-engineering-from-the-raspberry-pi
======
alias_neo
One thing the article entirely neglects to mention is that the well engineered
design came, via licensing, from an antenna specialist company called "Proant"

[http://www.proant.se/en/news/2017/03/01/raspberry-pi-
zero-w-...](http://www.proant.se/en/news/2017/03/01/raspberry-pi-zero-w-
nbi16.htm)

~~~
jcrabtr
There's a huge number of people involved in the design of the rpi. The antenna
is a great example of a subsystem designed by a separate team; another is the
new PMIC for the 3B+[1].

[1]: [https://www.raspberrypi.org/blog/pi-power-supply-
chip/](https://www.raspberrypi.org/blog/pi-power-supply-chip/)

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ChuckMcM
I would really like to have access to an antenna chamber like that one :-).
Lately I've been building/programming/characterizing SDRs and that generally
also includes antenna. I realized I had forgotten most of what I had learned
in school about electrodynamics so I've been refreshing all of those neurons
as well.

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...](http://www.awrcorp.com/products/ni-awr-design-
environment/microwave-office)

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wintorez
I'm far more impressed by Raspberry Pi Zero W than by the original or even the
latest Raspberry Pi. I'm using one as a streaming server for a security
camera, and also a web server, and its working beyond my expectations.

~~~
jhallenworld
It's nice, but I think you can't easily buy the chips. So still no good for
product design.

~~~
pjc50
You can buy it as a module, but this really isn't the Pi's intended target
market.

I've seen several commercial products that are just Pi-in-a-box, for small
runs it's fine.

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boznz
What is it with buying an RPi zero?

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 :-)

~~~
StudentStuff
Its definitely a loss leader with very limited availability, but thankfully it
did spur a wave of sub-$10 single board computers, most of which are on par
with much more powerful Raspis.

[http://linuxgizmos.com/worlds-smallest-quad-core-sbc-
starts-...](http://linuxgizmos.com/worlds-smallest-quad-core-sbc-starts-
at-8-dollars/)

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jhallenworld
It's interesting to understand the frequency dependency on antenna size by
studying the Friis equation. There are three cases:

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.

~~~
jeffreyrogers
Aren't the higher frequency bands wider so data rates are higher?

~~~
tonyarkles
Yeah, it's a really fun set of tradeoffs to play with. You're correct to a
first approximation. Channel bandwidth is is easier to come by at higher
frequencies (a 20MHz wide channel at 150MHz would be a giant swath of the
band, but a 20MHz channel at 5GHz is very small relative to the centre
frequency).

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.

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zokier
Without comparison to other typical PCB and/or ceramic antennas, it is pretty
difficult to judge from the article how good the RPiW antenna truly is.

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vkuruthers
Quite good performance from that antenna for it's size and cost yes. I wonder
what tools they used to design it?

~~~
jcrabtr
According to [1] (which has more info on the antenna design), the resonant
cavity antenna was designed by a company called Proant [2]. I remember reading
the the antenna is the same on the Pi 3 and Zero W. There are a few options
for PCB antenna design software out there, but I had never seen this type of
PCB antenna before the Zero W. Not sure what software they use, or whether
it's off the shelf or proprietary. Any antenna designers out there?

[1]: [https://www.raspberrypi.org/magpi/pi-zero-w-wireless-
antenna...](https://www.raspberrypi.org/magpi/pi-zero-w-wireless-antenna-
design/)

[2]: [http://mob.proant.se/en/home.htm](http://mob.proant.se/en/home.htm)

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barbegal
Typically you'd use a ceramic antenna on a product like this. What is the
difference in radiated efficiency between this antenna and a ceramic one? I'm
guessing there are other design considerations though, such as cost and
circuit board area consumed.

------
jmblock2
The ceramic chip antenna manufacturers are in a panic!

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mkesper
Someone needs to come up with a better unit for antenna efficiency. Which non-
expert can understand how much -3.5dB and -1.25dB differ?

~~~
spapas82
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).

~~~
logicallee
>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](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)

~~~
spapas82
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 :)

~~~
logicallee
Thanks for the followup! This was all quite instructive.

