Ken and Cortland and many others that entered this subject :
First, radiated emissions are best measured with radiated (not conducted)
measurements. There is a correlation between CM currents and RE but that's not
all (resonances, cable layout etc. count a lot).
Second, you say that CE are easier to measure than RE ? Agree if you talk about
emissions on AC power cords (as per CISPR22 and FCC part 15). But for the new
requirements on telecom ports, I suggest you to take a look at the new (3.ed.)
CISPR22 or EN55022 (sec. 9.5 + annex C.1) and may be you change your opinion !
Radiated emissions above 30 MHz are already covered.
If you wanna take care of lower frequencies (< 30 MHz) take a loop antenna
(remember the old VDE rules ?) and measure radiated H-fields with your system
in the same (typical) layout used for the higher frequencies (with whatever
cables you specify, UTS, STP etc.). I am sure that is much quicker, easier and
repeatable than all the nonsense (ISNs, CDNs, clamps, current probes,
capacitive probes, ferrites, 150 ohm resistors, signal generators, impedance
measurements, voltage measurements, current measurements and more) in the new
CISPR22.
As for the question of "outside world", I think in this ever more connected
world the border line between INSIDE and OUTSIDE is getting more and more
blurred, BUT I also think that a line must be drawn by the standard bodies,
otherwise it's gonna really get too much confusing (hope some CISPR/CENELEC
member gets it).
If we spill over the line (office, floor, building... whatever), emissions
requirements are triggered. But within that line it's to be considered an
"intra-system" (what's the system ? that's another good question to be settled)
interference potential and the manufacturer should take care of it without need
of enforcement because he has all the interest in making a product (system)
that works properly and reliably.
One last point: based on David Sterner's note, looks to me that North America
has a pretty extensive Ethernet and-the-like network. I honestly don't know if
the FCC has already enforced emission limits on LAN ports. Anyway, based on
David's note looks like there are no complaits of interference with TV and
telephones. And please note, this is the very bottom line of it. Emission
limits should be intended to protect public services ... and physics works the
same on both sides of the Atlantic... or not ????
My personal opinion ...
Paolo
-----Messaggio originale-----
Da: Ken Javor [SMTP:ken.ja...@emccompliance.com]
Inviato: giovedì 7 settembre 2000 18.43
A: Paolo Roncone; 'eric.lif...@ni.com'
Cc: 'emc-p...@ieee.org'
Oggetto: Re: R: Conducted Emissions on Telecom Ports
Although I don't work commercial EMC on a regular basis and I do not know
over what frequency range the telecom port CE are controlled (I assume here
150 kHz - 30 MHz), I believe that there is a mistaken premise inherent in
the comments to which I am responding. The purpose of controlling common
mode CE on any port is not to protect equipment at the other end of the
cable, or other co-sited cables, but rather to control radiated emissions in
a frequency range in which CE are easier to measure than RE. In turn, the
purpose of controlling RE is to protect broadcast radio reception.
----------
>From: Paolo Roncone <paolo.ronc...@compuprint.it>
>To: "'eric.lif...@ni.com'" <eric.lif...@ni.com>
>Cc: "'emc-p...@ieee.org'" <emc-p...@ieee.org>
>Subject: R: Conducted Emissions on Telecom Ports
>Date: Thu, Sep 7, 2000, 9:45 AM
>
>
> Hi Eric,
>
> I 100% agree with you. The scope of emissions standard should be to protect
> the "outside" (i.e. public) environment from interference. So only ports
> that connect to public telecom networks should be covered by the standard.
> The problem is (as pointed out in one of the previous notes) that the new
> CISPR22 / EN55022 standard clearly includes LAN ports in the definition of
> telecommunications ports (section 3.6) no matter if they connect to the
> "outside world" or not.
>
> Regards,
>
> Paolo Roncone
> Compuprint s.p.a.
> Italy
>
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