Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

Questions tagged [emissions]

52 questions
17
votes
6 answers

Failed radiated emissions test on USB cable - USB module hardware and firmware improvements

I posted a few days about ago how our product failed ESD testing. Well, it also failed radiated emissions testing so I thought I'd make a separate post. The product is a 5V USB powered, non-radio, 3v3 LDO regulated, 2 layer PCB inside a plastic…
Geo
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7
votes
4 answers

Radiated emissions from WS2812 LEDs

We have a product which is failing EMC testing on radiated emissions. It fails by approx. 25 dBuV at the peaks. The product has a large 550x900 mm opaque 5mm acrylic window. Behind this, at a 50 mm distance sit 300 2812 LEDs arranged in a 15 x 20…
srlevitt
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7
votes
2 answers

Twisted pair for mains AC load wiring?

Working on an enclosure in which there will be low voltage high precision circuitry (my area of more experience) coexisting with fairly high current (~15A) 120VAC load wiring (my area of less experience). Would be it be advisable to twist those AC…
ChateauDu
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7
votes
4 answers

How to fix EMC problems for existing designs?

I'm going to be looking at a few products that have failed EMC radiated emissions testing and will need to apply fixes in order to make them pass (unfortunately, in these cases, two of the designs can't be modified to fix the problem at board…
Amr Bekhit
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6
votes
2 answers

How good is coaxial cable?

My question relates to the accumulated AC voltage that will appear on the screen of a length of coax: If the cable is properly terminated at one end and fed with data (or any signal) at the other end, what will be the voltage on the screen relative…
Andy aka
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6
votes
5 answers

What could be generating this waveform in an EMC Compliance test?

We are having trouble with a CISPR-11 (EN55011) Radiated Emissions Class B compliance test in one of our solutions. The troubling part of it is basically an industrial motherboard (with a commercial SSD and commercial RAM) within a well grounded…
Javier Cambiasso
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5
votes
2 answers

EMC emission harmonics

I have a crystal associated with an Ethernet-to-PCIe bridge operating at 25 MHz. I observe spikes at 62.5 MHz and 312.5 MHz. Those harmonics are 2.5 times and 12.5 times the crystal fundamental frequency. My questions: Can the harmonics be 2.5…
user220456
4
votes
2 answers

When to employ RF shield cover on PCBA?

During reparations and teardowns I have frequently come across PCB-mounted RF shields and covers. While I don't typically work with GHz processors or design RF modules I wonder if such covers could be a way to efficiently avoid EMI issues in…
NoobPointerException
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4
votes
2 answers

EMI/RFI emissions and computer cases

I have designed a computer case (enclosure) for mini-itx motherboards. Its bottom and rear are made out of 2mm thick aluminium and the sides and top out of 4mm plastic (ABS). I'd like some advice please on EMI/RFI emissions. I am thinking of making…
user18459
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4
votes
3 answers

EMC 30-50 MHz emssions

I was trying to pass EMC tests for my 48V 5A BLDC driver and failed in 30-50 MHz range. I think I found the problem in my drive circuit, but I have a few questions that got me thinking, maybe someone can help me to answer. If my PCB is not too…
Eugen
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4
votes
0 answers

Do I need to get a device certified by the FCC if it uses the ESP32/8266?

I plan on making a device that the user can control with their phone via a WiFi connection to an ESP8266 or ESP32. If I end up selling this device, will I need to get it certified? The ESP32/8266 has an FCC ID written on it. Does this count, or do I…
888
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4
votes
3 answers

SIM900 Conducted Emissions Fail

I'm currently having trouble getting a product through EMC. Radiated emissions were comfortably under the limit, but conducted are failing badly. Here are the results: The noise appears to be largely common mode, with the exception of the first few…
Skov
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3
votes
2 answers

Density of braid shielding

Does the shielding braid density depend on frequency range to provide good cable shielding? I have read that braiding works well for low frequency but that at high frequency the effectiveness decreases because of holes.
Rishab
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3
votes
2 answers

PWM controller to meet EMI/EMC regulations

I'm designing an application in which the current running into a load is controlled by PWM. A microcontroller generates a PWM cycle at 20kHz and this signal is used to control a MOSFET which is directly connected to the load. The MOSFET operates at…
Francesco
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3
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2 answers

Why are radiated emissions standards for consumer electronics different from industrial?

Why are radiated emissions standards for consumer electronics different from industrial? Source:??
Will
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