The point is that RE/CE protect broadcast bands. Making an RE measurement
(E or H field, regardless) from a LAN line a couple meters long is not
representative of what you would measure if the LAN line were significantly
longer, as it might be in situ. Therefore a CE measurement can be better
correlated to predicted RE from a much longer line (at frequencies where the
tested LAN line is electrically short.
----------
>From: Paolo Roncone <paolo.ronc...@compuprint.it>
>To: "'Ken Javor'" <ken.ja...@emccompliance.com>, "'Cortland Richmond'"
<72146....@compuserve.com>
>Cc: "'emc-p...@ieee.org'" <emc-p...@ieee.org>
>Subject: R: R: Conducted Emissions on Telecom Ports
>Date: Fri, Sep 8, 2000, 3:51 AM
>
> 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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