Newbie require help for confirmation

Thread Starter


Joined Jul 29, 2013
Hi all,
I am currently doing a project to prevent Electromagnetic Interference(EMI) in a CPU.
My CPU consists mainly of ;
P8Z77-V DELUXE Motherboard
Power Supply Board M4-ATX
ADATA XPG SX900 SSD (hard disk)
h s marston 890sp-03000-a-100 (External Heat Sink)
h s marston cf1-0816-0400-0816a (Internal Heat Sink)
Thermoelectric Cooler and
a DC-to-DC converter.

I was wondering if there will be any EMF generated(i.e. Heat sink) inside the system. Another question that came upon me is that , the system runs on DC voltage but how does the signal travel from one place to another because signal are normally in the form of analog signal.

It would be good if someone could enlighten me.

Thanks in advance.


Joined Oct 2, 2009
The heat sink has nothing to do with EMI.
All switching circuits such as computer mother boards generate EMI.
To get an idea how much EMI, take an portable AM radio and place it on top of the mother board. Turn the tuning dial across the AM band and listen to the interference.

All signals in electronic circuits are analog. It has nothing to do with whether the power supply is DC or AC.


Joined Apr 27, 2013
Computers relay on the state of the signal line to be low (below 0.8V in most cases) or high (above 2V, depends on the system).

Thread Starter


Joined Jul 29, 2013
Thanks MrChips and LCD3.

I have a few more questions.

Q1: This question is about cable. Is it the higher impedance of the cable , the better the shielding of it?

Q2: cutoff Round waveguide. How much SE(dB) is enough . My project is working on 18GHz . I'm intending to use a honeycomb mesh , hence I relate that the thickness and the diameter of the hole are important factors.
The formulas I'd used were : f= (6.9x 10^9 )/ d and S = 32t / d .
After calculating , the diameter is 0.3833 inches and thickness of 0.71875 inches if I were to put 60dB(this magic number is given by my teacher and I don't know why) . Later I read on the formula , the book stated that" The maximum dimension of the holes is usually 1/8-in, and the panels are usually 1/2-in., thick, giving a t/d ratio of 4 and 128 dB additional shielding from the waveguide effect." from Electromagnetic compatibility Engineering. I wasn't able to figure out :confused: .

Q3: How much frequency can the following filters filter out? Because I went to their company website to check , they only state that it can filter out frequency. The data sheet does not even indicate whether it is a low-pass filter or a high-pass inductive/capacitive filter.
amphenol - ms3102e24-96s (RS-232 connector)
amphenol - ms3102e28-17p (VGA connector)
amphenol d38999/20wb2pn, size 11, 2way

I will really be thankful if someone could enlighten me.
Thanks a million