One of my jobs in the PC industry was regulatory compliance testing.
PCs (and their power supplies) must meet FCC and international specs for
both Radiated and Line Induced EMI before being marketed. Much more
often than not the cheap Asian short run knockoffs cut so many design
corners that they do not, nor ever could meet, the EMI specs. So those
companies cheat like hell on EMI testing and documentation in order to
get their products to market. By the time regulatory agencies catch up
to the problem, which is usually many, many months, that product is no
longer being produced (or the company doesn't exist anymore) therefore
no real action is taken. It then falls on the end user to clean up the
offending emissions. If one is fortunate enough to have the schematics
it is usually not much of a problem (for a Ham) to determine the cause
or causes. If not, then your usually shooting in the dark with a
shotgun.
Reid, K7YX
______________________________ Reply Separator
_________________________________
Subject: Re: [TenTec] DSP & COMPUTER NOISE
Author: "Ed Tanton" [SMTP:n4xy@att.net] at MSXGATE
To: <tentec@contesting.com>
Date: 7/20/98 9:39 PM
I believe the interference that can form on those 2 wires (and not be
filtered by components to ground from each of the two wires) is called
"common mode" and is definately a factor needing appropriate filtering. A
capacitor and transient suppressor is also desireable directly across the 2
wires.
At 07:30 PM 7/20/98 -0400, Carter Grabarczyk wrote:
>
>Steve Ellington wrote:
>>
>
>> And if you think about it, the cap between black and white is redundant
>> since the other two caps effectively bridge across them anyway.
>
>Not true...look at how all AC surge surpressors (or at least the better
>ones) are wired (and yes, I realize these are over-voltage devices, not
>capacitors). It's the old longitudinal vs transverse noise trick..
>
>73/Carter/K8VT
>
73
__________________________________________________________
Ed Tanton N4XY EMAIL: n4xy@att.net
189 Pioneer Trail
Marietta, GA 30068-3466 TEL: (770)579-3933 V/MBX/FAX
__________________________________________________________
INTERESTS: QRP BoatAnchors Test Equipment Photography
CW: 99.9% Mercury Paddle # 0214 QRP to 150W: 95%
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"Think you can, think you can't: either way you're right!" Henry Ford
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