6 ms·

Electromagnetic interference mapping

142 points by pizza 8y ago

lifeisstillgood 8y ago
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 8y ago
  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-preamplifiers/ https://interferencetechnology.com/diy-near-field-probes-pre...
dang 8y ago
Url changed from https://www.rtl-sdr.com/using-an-rtl-sdr-and-opencv-to-create-an-emi-heatmap-of-circuit-boards/ https://www.rtl-sdr.com/using-an-rtl-sdr-and-opencv-to-creat..., which points to this.
amelius 8y ago
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?
- deleted 8y ago
  [deleted]
- gloflo 8y ago
  It's fun, it's visual, it's a whole new dimension!
mysterydip 8y ago
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 8y ago
  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 8y ago
    If you have a decent oscilloscope, you can actually get pretty far with that and some DIY probes.
- Junk_Collector 8y ago
  It's worth noting that his bandwidth is only 2MHz on his SDR so this will require a lot of manual testing and tweaking for good EMI/EMC results. It might be useful for crosstalk but a directional probe would be better for that because you can account for trace alignment. A directional probe can be made in much the same way as his loop probe, but will be a mono-pole design and will probably require an amplifier.
xondono 8y ago
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.
- de_Selby 8y ago
  I don't think this is aimed at people doing certification though, it seems like it's more for the prototyping stage. It doesn't matter if the device isn't fully calibrated in that case.
  - xondono 8y ago
    Yes, I got that, but if you are closing a design loop around a noisy, bad aimed target, you'll get worse results.
- bravo22 8y ago
  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.
  - kaybe 8y ago
    Yes please! Finding the problem and fixing it is voodoo (including magical copper tape and metal charms for the wires..), any help is extremely welcome and can save so much money. (Even better if it improves upon the usual EMV divining rod.)
    - krapht 8y ago
      Do you not find problems in simulation? I used to do modeling in Ansys and CST Microwave Studio, and found them to be fairly accurate.
PaulHoule 8y ago
I remember doing something like this manually with a C-64 and oscilloscope in my high school physics lab.
- HNLurker2 8y ago
  Can you elaborate? Is this a project a freshmen can tackle?
  - PaulHoule 8y ago
    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.
homero 8y ago
What's the big antenna for?
krapht 8y ago
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 8y ago
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.

142 points by pizza 8y ago

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 8y ago
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-preamplifiers/ https://interferencetechnology.com/diy-near-field-probes-pre...

dang 8y ago

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

amelius 8y ago

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?

deleted 8y ago
[deleted]
gloflo 8y ago
It's fun, it's visual, it's a whole new dimension!

mysterydip 8y ago

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 8y ago
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 8y ago
  If you have a decent oscilloscope, you can actually get pretty far with that and some DIY probes.
Junk_Collector 8y ago
It's worth noting that his bandwidth is only 2MHz on his SDR so this will require a lot of manual testing and tweaking for good EMI/EMC results. It might be useful for crosstalk but a directional probe would be better for that because you can account for trace alignment. A directional probe can be made in much the same way as his loop probe, but will be a mono-pole design and will probably require an amplifier.

xondono 8y ago

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.

de_Selby 8y ago
I don't think this is aimed at people doing certification though, it seems like it's more for the prototyping stage. It doesn't matter if the device isn't fully calibrated in that case.
- xondono 8y ago
  Yes, I got that, but if you are closing a design loop around a noisy, bad aimed target, you'll get worse results.
bravo22 8y ago
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.
- kaybe 8y ago
  Yes please! Finding the problem and fixing it is voodoo (including magical copper tape and metal charms for the wires..), any help is extremely welcome and can save so much money. (Even better if it improves upon the usual EMV divining rod.)
  - krapht 8y ago
    Do you not find problems in simulation? I used to do modeling in Ansys and CST Microwave Studio, and found them to be fairly accurate.

PaulHoule 8y ago

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

HNLurker2 8y ago
Can you elaborate? Is this a project a freshmen can tackle?
- PaulHoule 8y ago
  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.

homero 8y ago

What's the big antenna for?

krapht 8y ago

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 8y ago

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.