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Questions tagged [emc]

Electromagnetic compatibility (EMC) is a branch of electronics related to identifying and solving problems caused by electromagnetic interference (EMI) between devices. It encompasses both attempting to prevent unwanted emissions from a device and also ensuring that emissions from another device will not cause spurious operation.

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2k views

Making aluminium conductive for an RF shield enclosure

I'm not sure if it's appropriate to ask here, but I would assume many people in electronics would have experience with this. I'm enclosing an RF sensitive PCB into an sealed aluminium enclosure. ...
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1answer
967 views

Crystal Harmonics EMC Failed

I have a failed on EMC Test 300MHz and 500MHz due to crystal harmonics. There is a lot of spike with a 25MHz harmonics. The first picture is the Top of the Board and the 2nd is the 2nd layer ...
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PCB design - signal loops

I've read about loops that a PCB designer should avoid them "mostly about ground loops" but i think I've read also about power. so in this case, is this wrong: ???
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160 views

How can I generate a noisy environment to test my PCB?

I am developing a PCB project but i want to use the PCB in noisy environments (which usually contains 7.5-45 kW multiple motors with frequency inverters and also ignition transformers). I made some ...
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1answer
413 views

Arduino Cellular Shield EMC Testing for FCC

I have designed an Arduino shield that uses an FCC pre-certified and PTCRB cellular module and I'm wondering about EMC testing and FCC compliance. However, the main concern here is that I am using a ...
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1answer
368 views

FCC Part 15 Class B Declaration of Conformity (DoC)

I'm familiar with Part 15 FCC testing for intentional radiators (3 meter limits of certain power, must be filed with FCC, requires accredited lab), but I'm a little unclear on the Class B ...
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198 views

Help with deciding my layout for EMC tests and SI. Different alternatives [closed]

I am thinking of what way would be the best to layout my system in order for it to have the best SI and pass EMC tests. My system consists of two PCBs joint by a flat flex cable (up to 7cm) and these ...
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How can I design a robust and professional power supply circuit?

I'm planning on doing a large project that would include an ARM microcontroller @ 50 MHz interfacing with a graphic LCD, user buttons, some sensors and some actuators (DC motors, valves) controlled ...
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359 views

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 ...
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721 views

Why does radiated emission of a PCB decrease as the frequency of the signal increases?

I was just reading Henry Ott's book "Electromagnetic Compatibility Engineering" and chapter 16.3.3 where he discusses how changing reference planes is detrimental to EMI. Quoting from the book: ...
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Difference between radiated and conducted emissions?

The company I work for needs FCC certification for an electronic product we are designing. I have watched a couple of YouTube videos on the subject but I’m not clear about the difference between the ...
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loop area and EMI

I always hear something like "reduce the loop area" when reading materials on EMI reduction. Why we need to minimize the loop area? I have two guesses: Smaller loop area will influence less signal ...
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933 views

At what point does the responsibility of the manufacturer end with regards to FCC/CE testing?

I'm curious as to when the responsibility of a manufacturer ends when dealing with emissions and RF testing, part of FCC and CE tests. I repair TVs as a hobby and as business. I got a TV in from ...
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2answers
514 views

What's the cheapest way to do basic EMI testing?

I need to test that my project will not interfere with radios in the 27 - 72 MHz band. I can't afford a spectrum analyser. Nor can I afford to buy all tx/rx pairs in between 27 and 72 MHz (27, 35, 47,...
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2k views

How to create EMI?

I want to subject my product to large amounts of EMI to see what happens. I figure I need the EMI to be broad-spectrum to be sure it will have the best chance of wreaking havoc. However, I don't ...
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163 views

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 ...
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MCU - What's going to happen if I put a PWM output pin right next to a bunch of ADC input pins?

I'm currently considering a MCU-driven circuit that will do a variety of things, including drive some BLDC motors and do some analog sensing (of position sensors, temperatures and the like). The ...
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4answers
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Why is a caseless PC not an EMI problem?

As I understand it, the case of a PC is metal so that it can form an EMI enclosure around the electronic parts. My view is reinforced by there being conductive fingerstrips around the mating edges. ...
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1k views

Dealing with splits in my ground plane

Whenever I'm making a cheap, 2-sided PCB, I run into this problem: Where I have signal lines (on the top layer here) running over top of a big fat power trace (on the bottom layer). Now, this is ...
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1k views

AC signal and ground plane with another trace passing between - is this bad?

In learning about reducing a circuit's EMI emissions, I've learned the importance of a ground plane, in that it allows the current-return for an AC signal in an adjacent layer to flow directly under ...
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193 views

Spike killer - Why does it reduce spikes?

This application note says that the spikes when the diode stops conducting its due to its reverse recovery time. I thought that the spikes were occuring due to the parastic inductance and the ...
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2answers
288 views

Open-loop Buck LED dimming

About this buck LED driver... TL/DR the questions: 1) I intend to drive the FET from a microcontroller PWM via a suitable FET driver. This open loop control scheme seems too simple. Is it a trap? I ...
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293 views

Does a saturated inductor radiate more?

Background: I am using a shielded inductor in a switching power supply, and am investigating an EMI issue. My hypothesis is that since the inductor is saturated, the magnetic field is no longer ...
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1answer
603 views

Making conducted EMI measurements in the presence of building-wide ground-fault protection for personnel?

As is documented here among other places, the Line Impedance Stabilization Networks used to make measurements of conducted EMI as per CISPR 22, FCC Part 15, and suchnot contain large line-to-ground ...
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496 views

EMC Design Precaution

I'm designing a simple circuit which will charge a big capacitor for 3 seconds, then pass a 5A current for few microseconds, then charge again the big capacitor for 3 seconds, then pump again 5A for a ...
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How can a shield winding in the transformer be helpful without fully covering the core?

This article describes the Apple iPhone charger circuitry in great details. It mentions the shield winding in the flyback transformer. The shield winding is simply an extra most outer winding and the ...
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241 views

Why are engine spark plugs w/o resistor so potent killers of electronics nearby them?

I've recreated the ignition coil part of a small Honda ICE (typically used in lawn mowers or single-digit kW gensets). I use an electric motor to turn a flywheel taken from a dead engine, and I've ...
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2answers
669 views

FCC-approval and "modular" integration

I see that a PCB requires certification even if it incorporates a certified RF module, so EMC tests for spurious emissions will still be needed. Is FCC-approval needed if a Raspberry Pi is shipped/...
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209 views

Kick-off Spread Spectrum Clocking

Need of SSC: Spread spectrum clocking (SSC) is a special way to reduce the radiated emissions of digital clock signals. These levels or energy is radiated and therefore this is where a potential EMI ...
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1answer
682 views

Return Paths of Signals on Flat Flex Cable

I have a 4 layer PCB with a typical stackup (signal-gnd-vcc-signal) and on the top layer there's a CMOS sensor connected with a flat flex cable... I was wondering, since there's no reference plane ...
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TFT LCD pixel clock filtering

I would like to know how to filter the pixel clock in order to reduce emitted radiations. Block diagram The LCD controller is part of a motherboard. A board, connected at the other side of the FFC ...
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1answer
353 views

Looking for good articles about reducing crosstalk and other noise in PCB design

I am designing a rather large PCB with straight parallel traces 20cm long carrying CMOS logic at around 100kHz. On top of that I have 8 MOSFETs supplying 5A switching on/off at around 400Hz which a ...
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909 views

Class D power supply filtering for conducted emissions

I have recently designed an audio player that uses the TI TPA3112D1 power amplifier, and mostly based it on the reference design and schematic. I find however, that the design is failing the ...
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655 views

Power and Ground planes The Henry Ott way or split ground planes

Seeing a lot of mixed infomation around involving ground planes on multilayer boards. For a mixed signal mulitlayer PCB which is the preferred method? I know every board is different and it depends ...
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1answer
2k views

Common mode choke in circuit with multiple ground connections

I'm designing an automotive circuit where I'm using a reference power design from TI. Together with protection circuitry, this design includes a common mode choke. The same circuit has an antenna ...
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2answers
231 views

Thickness of low frequency Mu shield calculation

I am dealing with a low frequency varying magnetic field, say 10 - 100Hz with a magnitude of 0.8T. It seems shielding at this frequency gets tricky. Even though Mu is capable of doing it, there should ...
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1k views

How to maintain EMI shielding whilst penetrating the shield with cables?

I'm trying to shield an ip camera from EMI generated image noise for low light photography. It's enclosed within a metal box that is then grounded. The subject is also inside the box. The camera ...
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1answer
158 views

Cable shield as ground conductor

I have two circuits connected by a shielded cabled. The cable brings 3.3V DC and LVDS communication between the circuits. The shield is being used as the sole conductor for the reference ground to the ...
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1answer
259 views

STM32 microcontroller families and environment conditions (F4 vs G4 vs F7 vs H7)

I want to refresh some product with old PIC18F and use STM32. New product requirement is 8 UART interfaces, a bit more DMIPS and more memory. I probably could use STM32F0 or F1, some UART multiplexing ...
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1answer
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Ground planes disposition in Ethernet connection

I am designing a board that will have sensible analog signals and a processor communicating with the external word via Ethernet and I want to avoid that common mode currents couple into my analog ...
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1answer
336 views

Suppressing "travelling" EMI spikes

I am working on a circuit with a AC to DC power supply module and wireless MCU module. The MCU operates at 240MHz and on the power input to the module there are 2 x 0.1uF capacitors and a 22uF ...
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489 views

Steps needed for low EMI PCB design

As a student, when I needed to make a PCB, I just placed the components & auto-routed on ARES, and they usually worked well. However, now a fresh graduate & novice engineer, I found that this ...
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1answer
216 views

Will FCC EMC tests need to be redone?

In light of the new FCC rules that Chinese (and all non-MRA) labs will no longer recognised in July and all EMC tests need to be done at FCC-authorized Telecommunications Certification Bodies, for FCC ...
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1answer
1k views

Long wire PWMed LED lights

so I plan to build a house (at some point in future) and I'd like to implement some sort of home automation. Now one of the things I'd like to have is PWMed lighting. Most of the lights would be 12V ...
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Where to connect shield and ferrites in PCB with isolated planes

I have a device which has two sections of the PCB completely isolated form each other, but connected by an isolator IC (PN: ????). I think I need to shield the whole device for reducing EMI because ...
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69 views

Layout of multichannel 20-bit DACs

I've been reading various app notes as well as Ott trying to figure out how to lay out multiple converters on a board. Most explain how to route the data lines but not much about routing the power ...
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410 views

Why are "devices utilized exclusively in any transportation vehicle" exempted from FCC compliance testing?

I was researching whether do we need to do FCC compliance testing for a device we developed for a client. Curiously, it seems to be in the list of exemptions (passage taken from here): A digital ...
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636 views

How to detect far field noise outside of a certified EMI lab?

For some background, we recently took a product to the EMI lab for EMI Pre-compliance testing and came close to passing, but we have some issues in the 30 to 100MHz range that just put us out of ...
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1answer
161 views

Sequencing modes for FCC "Intentional Radiator" test

I'm FCC certifying as an "intentional radiator" a product that uses a custom antenna and off the shelf Broadcom WiFi module. The module has an antenna port, so single-modular and limited single-...
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3answers
1k views

safe to use an unshielded jack for 10Mbps Ethernet?

I have a hardware device which includes Ethernet connectivity. I have a surface-mount Ethernet jack, with top entry (as opposed to right-angle). Part number is RIA Connect AJS03B8813, if that helps. ...

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