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N9038A MXE EMI Receiver - Conducted / Radiated Emissions

Question asked by Zack on Jul 27, 2016
Latest reply on Nov 14, 2017 by bchen94
  • Comment • 1


1) For conducted emissions, should the EMI mode be always set to DC coupling? We noticed when set to AC there would be a high noise floor on the frequencies below 1 MHz.

2) For radiated emissions, Should we keep the EMI mode at AC coupling?

3) It's constantly asking us to keep the receiver aligned. Is this normal? It takes 5-10min to do the full alignment.

bchen94
bchen94 Employee Nov 14, 2017 11:25 AM
Correct Answer

Hello, Zack!

 

For reference, this is the product in question:

 

http://www.keysight.com/en/pdx-x201870-pn-N9038A/mxe-emi-receiver-3-hz-to-44-ghz?nid=-32508.1150210&cc=US&lc=eng&pm=ov&state=0

 

On that product page, if you go to "Resource Center" and find tab "Application Notes", there is one titled "Making EMI Compliance Measurements - Application Note". Click on it, and it'll prompt you to fill in some information, then you can download it.

 

In the AppNote, it considers conducted emissions testing to be between 9 kHz and 30 MHz, and radiated emissions from 30 MHz to 1 GHz (or higher, like stated.)

 

  1. This is not a matter of what mode the receiver is in, but rather how the two coupling modes themselves work - the AC coupled mode's lower limit is 10 MHz, but specifications are always written with leeway, therefore you are seeing the high noise floor at 1 MHz. The way that AC coupling circuits work is that there is a capacitor to filter out low frequencies, therefore in this range DC coupling mode is preferred. Page 8 walks you through a conducted emissions measurement.
  2. Depends on what frequency range you are trying to measure. AC and DC modes have tradeoffs depending on the range, so you would want to manually change it back to DC mode if you're also trying to measure lower frequencies in radiated emissions. But if your range of interest is same as mentioned in the AppNote, then you can stick with AC coupling. Page 4 and onward details different international regulations. Page 12 is a good guide on radiated measurements.
  3. Without any context as to what you are doing, yes this is a normal alignment for a receiver. Does it prompt you to keep aligning after an alignment? Does it force you to align each time? A workaround might be to turn the auto-align off after the initial alignment, do the measurement, and then turn the alignment back on.

 

Hope this helps!

Bertie

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