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William Murray

EMC Problems in Modern Electronics

William Murray
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BillWM
BillWM
12/1/2013 3:10:43 PM
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Re: Re : EMC Problems in Modern Electronics
3G -- to get the full power one must be holding the phone during a data call -  Know what you mean about base-stations and occupied buildings -- just should not be permited for buildings occupied by people -- each carrier added significantly increases peak power -- plus the limits were set for an 8 hr working shift , not 14 hrs in a dwelling -- a bad call on the limits by regulators -- one can easily put a tower on a rooftop to get the antennas further from the occupants

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Victor Lorenzo
Victor Lorenzo
12/1/2013 3:01:54 PM
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Re: Re : EMC Problems in Modern Electronics
@William: "the heating due to a cell phone is less than 1/1000th the heating due to a microwave oven"

Microwave ovens use to output about 1kW, class 1 3G phones put about 2W on the air.

In Spain it was found that some correlation exists between cancer incidence (leucemia) and long term expossure to radiation coming from massive 2G/3G mobile antenna sites (usually over the buildings).

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Victor Lorenzo
Victor Lorenzo
12/1/2013 2:50:21 PM
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Re: RF vs EMC
"To use ferrites for power line applications you have to use differential mode" This type of ferrites are specially usefull in the case of common mode conducted emissions (common mode noise) to avoid the power line to act as an antenna. For other noises you will need line filters (ferrites and capacitors combined to form a low pass filter).

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DaeJ
DaeJ
12/1/2013 2:27:58 PM
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Re: Shielding levels
->Under high intensity external electromagnetic fields (EMI), the induced voltage in one PCB track (e.g. data line from external flash to MCU) is directly dependant on the area covered by the signal path for that track.

On this type condition, I highly recommend that ground isolation would be beneficial for noise and radiation suppression. For example, high voltage and low voltage could be separated in the ground view point, if high intensity external electromagnetic is caused by high voltage current closed to data line.

   

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BillWM
BillWM
11/30/2013 12:52:59 PM
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Re: Re : EMC Problems in Modern Electronics
Cell phone radiation is non-ioninzing radiation -- meaning it cannot cause chemical bonds to be broken -- it can still produce a small effect due to heating and stiring of the molecules  -- the heating due to a cell phone is less than 1/1000th the heating due to a microwave oven.   Statisticaly the largest single risk is distraction while doing a safety critical task like driving -- texting and driving, or carrying on an emotional conversation while driving etc.

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yalanand
yalanand
11/30/2013 12:30:58 PM
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Re : EMC Problems in Modern Electronics
@Murray, Thanks for the post. I agree with you that radiation and interference is the serious issue at present days. Not only at FM transmitters ,mobile  phone antennas too causing this interference problems  to electronic devices.  More over this radiation is causing health problems  too.

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eafpres1
eafpres1
11/30/2013 12:20:24 AM
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Re: RF vs EMC
Hi Vishal--To use ferrites for power line applications you have to use differential mode.  This means the power and return lines must pass through the same core.  The way that works, is that the time-dependent power currents cancel each other and the core attenuates noise currents that are one one line or the other (but not both).  Since the power currents cancel, the net attenutation of them is 0.  Thus, the ferrite core selectively attenuates noise.  In many cases a cylindrical core is used, but for board-traces there are SMT designs that can handle 2 or more lines.

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Vishal Prajapati
Vishal Prajapati
11/29/2013 8:30:09 AM
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Re: RF vs EMC
@eafpres, thanks for your suggestion. It looks like you are suggesting to keep only antenna outside the shield and all others including LO, IF and other filters to be inside the shield. As you suggested conducted EMI can be reduced by ferrite beads. Can it be applied to power lines also?

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eafpres1
eafpres1
11/28/2013 12:03:25 PM
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Re: RF vs EMC
I agree conducted EMI must be addressed by other means. One common way if RF choke in either common mode or differential mode, using soft ferrite like chip beads or array. In some cases even narrowband ceramic filter or SAW filter may be needed.

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eafpres1
eafpres1
11/28/2013 11:59:57 AM
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Re: RF vs EMC
For the slits the equation is basically like a cutoff frequency related to opening size. However there can be conducted interference so what you see in test may not match the calculation exactly. Also consider some designs allow use of one piece shield with no openings--the shield is soldered all the way around. In my experience the designers try to get entire RF section including filters etc inside the shield.

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