Noise and interference

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Question by Fransico Wong posted 15 May 2000
icon Noise and interference
I got a number of Cat5 network cables running just 1 inche beside my 19" monitor. Would there be any interference or problems. By the way, my cable modem is also within 1 inch of my monitor, would the cable modem be affected?

Thank you.

Answer by Dmitri Abaimov posted 16 May 2000
icon Dear Fransico,
When it comes to electromagnetic compatibility, it's a frequency that matters. Just because most of the noise that comes on substantially different frequencies, is filtered out by a device's receiving circuits.

Most of the electromagnetic field that is produced by your monitor is within 100kHz range if you run up to 1600x1200 screen resolution, 85Hz refresh rate.

Hopefully, this frequency is too high to interfere with analog phone signal and too low for Ethernet signals.

Besides, the device you're using should be FCC Part 15 Class B compliant. That means it produces less than 100mkV/m of electromagnetic field strength over 10 feet distance in that frequency range. When it's converted to the strength on 1 inch (120 times closer) distance, it's still within the limit that's set for CAT5 cables 3V/m.

So, it may be a problem when you run similar frequency application like balanced VGA signal to remote LCD projector. But if you run voice or Ethernet, I don't see any problem. This noise will not come through.

With regard to the cable modem you have - the receiving signal itself should not be a problem since it's measured in hundreds of MegaHerz, but there may be some circuits inside of the device that operate on similar frequencies to the monitor. It may or may not be a problem - if the device itself works normally - you'll get good connection.
To learn more about the EMC issues, you're welcome to read the document, recently published by Cabling-Design.com. Browse to the Document Section of the website to read it.

I wish you have no EMC problems at all.
Dmitri Abaimov, RCDD

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