Conducted Emissions - Accurate Pre-compliance EMC test results (automotive)

[@angelodemichele]

Hi, why did you use two lisn? One lisn was that enough?

[@furiousbullet]

I am also curious of this

[@angelodemichele]

​@@furiousbullet hi, from the tekbox manual that you can find on the lisn manufacturer's website: if the DUT is grounded to the vehicle chassis with a power return line shorter than 20 cm, a single 5μH LISN is sufficient and the conducted noise will only be measured on the positive supply line. If the power return line of the DUT is longer than 20 cm, two 5μH LISNs are required. The positive supply line is connected to the DUT via one LISN and the power return line is connected to the DUT via another LISN.

[@joselopezbernal7849]

Very well done

[@MachOneDesignEMC]

Thank you! Cheers!

[@marcin8132]

Hello, I am wondering why in the tekbox setup there is a significant higher noise floor from 30MHz? Second question, should LISN ground connection be connected from both sides? Thanks for the answers :)

[@MachOneDesignEMC]

Hi Marcin, that is a great question. I was wondering the same, then I checked Murata's set-up, apparently, they used a low noise amplifier between the LISN and the spectrum analyzer. if you connect a Low noise amplifier (LNA) before you SA, you lower the noise figure. That is why. But I don't think you need that for conducted emission test.

[@marcin8132]

@@MachOneDesignEMC Thank you for your quick reply. Could you share with us Murata's document used for this comparison?

[@topQuark12]

The Murata app note radiated test only goes up to 300 MHz, but I want to validate my setup up to 1 GHz for radiated test, do you know of any good boards for this purpose? Thanks!

[@MachOneDesignEMC]

i was searching, will let you know once i find sth. let me know if you find sth as well

[@shridharchendake8586]

Hi, is there any external preamp used on the measurement line from LISN?

[@yeaveny3629]

Can you tell me whether USB chargers plugged into the cigarette lighter socket are regulated under CISPR 25 (EN55025)?

[@MachOneDesignEMC]

This is a great question. I would assume yes

[@yeaveny3629]

@@MachOneDesignEMC Thank you. I assumed so too, due to the fact that the device is plugged into the car's mains. However, when I started to check how the labs in China test it they don't use CISPR 25 standards at all (they don't use 5uH LISN etc.), they just "test" like a normal multimedia charger under CISPR 32 (EN 55032). The result is that it is difficult to find a car charger that does not cause interference - even audible on the radio, let alone passing EN 55025.... I have checked a dozen such chargers bought online and in supermarkets. And I began to wonder whether I was actually exceeding the requirements. There is also EN 50498 - but I don't have it and don't know what levels are required, nor do I have the receiver scripts for it.

[@balazsmarki9475]

Hello, Thanks for the nice video! It made me curious if my home test setup can give me similar results. Can you share which Murata document you used?

[@MachOneDesignEMC]

Hi, sorry for the late reply. it is community.element14.com/products/manufacturers/murata/m/files/382

[@oly463]

What is the rf seal achieved on the tent door ? , It appears to be velcro ?

[@MachOneDesignEMC]

Hi Peter, yeah, it seems like it. But they must have added some meshed conductive material to make it seal tight.

[@plinsburg]

Hello, thank you for the video. I have a question. When you use a battery, what did you connect the ground plane to? I'm using the Ground contact from the bench power supply but I have much higher noise floor. 30dBuV with 100kHz bandwidth. Reducing bandwidth helps to lower the noise floor, but 100kHz is mandated by the standard. So I'm curious what can I do with the power supply and the ground plane in order to help the situation.

[@MachOneDesignEMC]

Hi Denis, the LISNs need to be connected to the ground plane either via a 1uF cap or short. See www.tekbox.com/product/tblm1-lisn-mate/. To keep the noise floor low, you either put the DUT in a tent like I did. Or choose a time where lots of equipment in your office/workshop are switched off. Be aware of the LED lights, they are terrible emission sources that can easily push up your ambient noise. I noticed that the LED ceiling lights in my office pushed the ambient noise by at least 10dB. so I always switch them off. Bandwidth wise, yes, below 30 MHz, RBW is 9kHz, from 30MHz, 120kHz.

[@plinsburg]

@@MachOneDesignEMC Thanks, I 100% agree with the point about LED lamps. I do connect the LISN to the ground metal plate of course. The question was, should I connect the ground plane itself to something "grounded" while providing the power from the battery. The battery does not have a ground terminal as a bench power supply does. So should I, for example, connect the ground plane to the ground knob of the power supply while providing the power to the system from a battery? Or should I connect the ground plane to the negative terminal of the battery?