
Electromagnetic interference mapping - pizza
http://charleslabs.fr/en/project-Electromagnetic+interference+mapping
======
lifeisstillgood
This is the most awesome thing I have seen on HN for weeks.

It marries such distinct component disciplines together to come up with a
simple, immediately graspable device.

Being able to see radio waves has long been a wish of mine - we walk through
this invisible world suffused around us, and anything that steps towards
revealing that world I am a fan of.

~~~
donquichotte
Agreed! And every component is highly complex, i.e. the design of the probe
[1], or object tracking in videos. While the author is obviously standing on
the shoulders of giants, he appears to be pretty tall himself.

[1] [https://interferencetechnology.com/diy-near-field-probes-
pre...](https://interferencetechnology.com/diy-near-field-probes-
preamplifiers/)

------
mysterydip
This is excellent! EMI testing is one of the things I have to do with my
projects, but there hasn't been an affordable way to visualize them. I've
played with an RTL-SDR for ADS-B traffic so this is right up my alley. I'll be
sharing this with coworkers for sure!

~~~
jononor
Got any resources on EMI testing on the cheap? Would be a great thing to share
in our makerspace, as many do semi-professional electronics.

~~~
xondono
If you have a decent oscilloscope, you can actually get pretty far with that
and some DIY probes.

------
krapht
This is pretty neat! The next step: create an array of common-clocked RTL-SDRs
connected to patch antennas, and mount them on a rail. Use beamforming
techniques so you don't have to manually wand the device. Connect an antenna
to a signal generator to roughly calibrate your array response. Slightly more
expensive (the big cost would be a signal generator, but a lab should have one
of these anyway), but a lot more potential for automation.

I actually built something similar to the above setup for work, years ago.
RTL-SDR wasn't available back then, so it was a lot more expensive. It would
be awesome to go back and do it over again, just to see how much it would cost
today.

------
asteli
I'm doing EMC work at the moment. I've fantasized about putting a near-field
probe on a 2-axis motion stage and building a 4-dimensional (X, Y, Frequency,
Power) visualization with the data.

The place I work is pretty well outfitted, so I imagined it using a spectrum
analyzer, a couple of Zaber motion stages we have sitting around, and a nice
set of H- and E-field probes. Probably several thousand dollars worth of
equipment.

Now, reading Charles' blog post, I'm blown away by how he's basically done the
same thing in a very clever way using about $50 worth of parts.

------
PaulHoule
I remember doing something like this manually with a C-64 and oscilloscope in
my high school physics lab.

~~~
HNLurker2
Can you elaborate? Is this a project a freshmen can tackle?

~~~
PaulHoule
Get a loop of wire, hook it up to the oscilloscope, read the amplitude of the
oscilloscope.

Move the loop and repeat.

I did this in the late 1980s in my high school physics lab. We had a bunch of
tube-type Textronix oscilloscopes that we inherited from the Raytheon factory
where they made Patriot missiles. When they broke we shuffled parts around
between them to keep them working, the way my physics teacher did when he was
in the air force.

The preamp stage of the oscilloscopes were good enough that we didn't need any
extra electronics to do the work.

------
xondono
While it's a nice hack, the problem with the EM certification world (and why
it's so expensive) is not about the devices themselves but about calibration
and measurement stability.

Most EE will be able to guess the patterns this setup generates just by
looking at the boards themselves.

~~~
bravo22
This is useful when you fail your EMC testing. You have a baseline measurement
and you're looking at relative change. For example you may have be over the
limit by 6dB at 430 MHz. You would take a reading using this setup, and
normalize it against your lab plot.

You then try a number of fixes, and take readings using this setup. It is easy
to determine if you're close to 6dB drop that you need.

~~~
xondono
The problem is that even with a professional setup you should expect about
+/-3dB tolerances.

Since there’s no expectation of that uncertainty being systematic, taking a
relative change pushes your error bars +3dB.

That 6dB drop is under the error bars, so it’s pretty meaningless, and that’s
with a professional setup.

In other words, there’s no expectation that the numbers you’ll get from these
will translate into anything useful, at most you have a ‘hotspot’ detector.

~~~
bravo22
Professional setup has much tighter tolerance than 3dB. I was using 6dB as an
example. Usually you're trying to kill peaks that are 10-20dB over.

This kind of debugging is very routine. You do it manually with E/H field
probes and a spectrum analyzer in between lab visits. This setup makes it more
repeatable by automating it.

~~~
xondono
>Professional setup has much tighter tolerance than 3dB.

To comply with CISPR (as an example), a lab only has to validate <4.5dB (in
the 30 MHz to 300 MHz range), and up to 5.2 dB (from 30 MHz to 1 GHz). See for
instance [1].

By the way, if you are doing this kind of testing routinely, you need to check
your PCB layout process. This fine grained tweeting should be a last resort
option.

[1][http://ing.univaq.it/emc-chap-
it/download/MUinEMC_Revision%2...](http://ing.univaq.it/emc-chap-
it/download/MUinEMC_Revision%20of%20CISPR%2016-4-2%20doc.pdf)

------
amelius
I don't understand the need to build a video image out of the information.

Why not link the probe to a buzzer/led, so it tells you when the interference
is high as you sweep the probe across the device?

~~~
gloflo
It's fun, it's visual, it's a whole new dimension!

------
homero
What's the big antenna for?

------
dang
Url changed from [https://www.rtl-sdr.com/using-an-rtl-sdr-and-opencv-to-
creat...](https://www.rtl-sdr.com/using-an-rtl-sdr-and-opencv-to-create-an-
emi-heatmap-of-circuit-boards/), which points to this.

