Re: Telecom ISNs for CISPR 22:2006

[neven11]

I'd be very curious to see what the others think of the clause that Bill
quoted.

I know the standard specifies ISN and it is "available" - if the definition of
available means one can buy it. Therefore it can be read as ISC "shall" be
used. I also know that what the standard specifies does not always mean it is
appropriate, and if there is any chance I could use any cllause that says I am
OK to use some of the clamp methods, I'd opt for it.

The ISN does not necesserily make it worse, it can make the result better too.
The point is that the effect of thje ISN on the signal and the test results is
not well defined. The same goes for CND for condicted immunity.


Neven


From: "Bill Owsley" 
To: neve...@comcast.net, "jim hulbert"  , emcp...@aol.com
Cc: emc-p...@ieee.org
Sent: Friday, March 6, 2009 7:22:14 AM GMT -08:00 US/Canada Pacific
Subject: Re: Telecom ISNs for CISPR 22:2006


 
Would this have any bearing  on which test method can/should/shall be used? 
Or is this only for the soon to be past?
EN 55022:2006 

Endorsement notice 

The text of the International Standard CISPR 22:2005 was approved by CENELEC
as a European 

Standard with agreed common modifications as given below. 

COMMON MODIFICATIONS
...
9 Method of measurement of conducted disturbance at mains terminals 

and telecommunication ports 

9.5 EUT arrangement 

9.5.1 General 

Add the following paragraph at the end of the subclause: 

Where alternative test methods are described in the following subclauses,
compliance with the 

requirements of the subclause may be demonstrated by either or any of the
methods 

described.
 


- Bill
Indecision may or may not be the problem.

--- On Fri, 3/6/09, emcp...@aol.com  wrote:



From: emcp...@aol.com 
Subject: Re: Telecom ISNs for CISPR 22:2006
To: neve...@comcast.net, jim.hulb...@pb.com
Cc: emc-p...@ieee.org
Date: Friday, March 6, 2009, 12:12 AM



Hi Neven,
 
I agree with this statement, however the standard specifies ISNs for 
common
interfaces such as Ethernet. So I think we are stuck with using ISNs whenever
possible. The capacitive voltage clamp and current clamp methods are left as
an option for when there is a non-supported telecom interface.
 
Thanks,
Tim
 
 
In a message dated 3/5/2009 2:07:52 P.M. Pacific Standard Time,
neve...@comcast.net writes:


For high-speed differential interfaces (e.g. Ethernet) I'd 
strongly prefer
any non-invasive method over effectively cutting into the cable and adding an
ISN/TLISN in series, which changes the characteristics of the cable under
test. That is especially so because of the mode conversion in the Ethernet
connectors (one on each side of the ISN/TLISN), possibly exacerbated by poor
layout inside the ISN, and with (in my strong opinion based on a lot of work
there) inadequate specification of the balance (LCL) which only takes into
account balance of the individual pairs and not their coupling and conversion
caused by the inter-pair coupling and conversion which is considersable.

Regards, Neven



- Original Message -
From: " Jim Hulbert" 
To: "emc-p...@ieee.org" 
Sent: Wednesday, March 4, 2009 11:44:28 AM GMT -08:00 US/Canada 
Pacific
Subject: RE: Telecom ISNs for CISPR 22:2006



What is the opinion of this group on the alternative method of 
C.1.3, using
a current probe and capacitive voltage probe?

 

Jim Hulbert

Pitney Bowes

  

From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Pettit, 
Ghery
Sent: Wednesday, March 04, 2009 1:41 PM
To: Pettit, Ghery; emcp...@aol.com; EMC-PSTC@LISTSERV.IEEE.ORG
Subject: RE: Telecom ISNs for CISPR 22:2006

  

Update.  It turns out that at least one vendor is making ISNs both 
ways.  I
can’t say that one design is preferred over the other as the standard
does not make that statement. 

  

Fun thing about this business, you’re always learning something new. 

  

Ghery 

  

  

From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Pettit, 
Ghery
Sent: Tuesday, March 03, 2009 4:20 PM
To: emcp...@aol.com; EMC-PSTC@LISTSERV.IEEE.ORG
Subject: RE: Telecom ISNs for CISPR 22:2006

  

Interesting question, and one that made me look carefully at CISPR 22 
and ask
questions of the other members of CISPR SC I WG3.  Here’s what I have
found out so far  - To the knowledge of the members of the working group (at
least, those who commented), other than some gold units made for
investigations back in the 90s when the 

Calmp to GND in FXS/FXO/xDSL....

[neven11]

Please, can anyone help me clarify this? In telco interfaces, e.g. FXS, FXO,
xDSL, if I have a clamp device for lightning protection connected from lines
to the safety GND, is the safety isolation requirement still met? Assume that
without the clamp device all the clearances and hi-pot are OK. Thanks, Neven -
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http://www.ieeecommunities.org/emc-pstc From: Doug Nix To: Peter Cc:
emc-p...@ieee.org Subject: Re: Machinery safety and emergency switch Date:
Fri, 29 Aug 2008 14:42:42 + Content-Type: Multipart/alternative;
boundary="NextPart_Webmail_9m3u9jl4l_15979_1220068411_1" 
Peter,

I realized this morning that I neglected to discuss the question of adding
e-stop devices in my message last night. Nick was correct in stating that
e-stop device must be daisy-chained - that is they must be connected in
series, not in parallel as you suggest in your message, Remember that a basic
requirement of the emergency stop is that it must override all other controls,
the operator device must require manual reset, and reset of the e-stop system
cannot re-start the machine, only permit the re-starting by other means.

The outcome of your risk assessment must be used to determine the degree of
control reliability required from the system. This will determine the need for
single or dual channel construction and monitoring requirements.

-- 
Doug Nix, A.Sc.T.
IEEE PSES&n bsp;
Kitchener-Waterloo Section, Ontario, Canada

d...@ieee.org 
mobile (519) 729-5704
fax (519) 653-1318

Find me LinkedIn at http://www.linkedin.com/in/dougnix


On Aug 28, 2008, at 15:43, Peter wrote:



Hi experts,
 
I have a question about requirements for emergency switches used in 
machinery
placed on market in EU.
The machine complies to MD by compliance with amongst others EN 
60204-1:2006
and has a full compliant emergency switch installed for USERS easy activation
during normal use.
 
Now my question is i have no where seen a requirement that another 
emergency
switch should be available for SERVICE personel on say the back side or other
place of the machine, as he/she might not have easy access during a service
situation. The machine is not very large but a service person might not be
able to reach the normal users switch when working on the back f.ex.
 
Can anyone point out a requirement in EN 60204-1 or any other MD related
standard that states the need for this ?
The service person can of course disrupt the power using the main safety
switch off device (lockable), and further he is expected to be somewhat more
aware of dangers related to his job.
 
Another question, is it allowed to add several emergency switches in 
parallel
with the existing if wanted (currently it has one NC and one NO contact
connected through a safety relay), but it would be possible to add screw
terminals for further expansion (limited only by relays capacity) if needed.
 
Hopefully above makes somewhat sence and a machinery experts likes to 
comment
on this, have a nice day.
 
Best regards
Peter
 
 
 
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48V supply on VoIP

[neven11]

On powered Ethernet interfaces, 48 VDC is delivered from Ethernet switches to 
IP phones with + over one twisted pair and - over another pair of a CAT5 cable. 
The power is not permanently connected to the connector or cable. It is 
switched to the socket/plug only if an IP phone is detected on the other end of 
the cable. If someone disconnects the phone, the power will be disconnected 
from the socket by a switch (or relay).

In the integrated types of connectors/socket, with transformer and some other 
components built-in, the distance between + and - of 48V can be as little as 
0.02" on a surface of a little PCB. 48 V over 0.02" gives E field strength of 
94 kV/m.

Is there any safety or reliability concern with 48V possibly permanently across 
0.02" spaced pads on a PCB surface? I believe safety-wise it is okay, but I am 
not sure if electromigration or something else may cause long-term problems, 
since the phones are more-less permanently connected.

Any comments? I am not particularly interested in the power-supply design 
aspect, but more in this specific situation with 48V across small creepage 
distance.

Thank you, Neven

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RE: EMC E&H close field probes / Mindcruiser

[neven11]

Agreeing with both, I wish to add that while the probes are very useful in 
locating the source and are not (very) useful in predicting the absolute level 
of far-field emission they may be also useful to predict relative far-field 
difference in emission, because with all other things equal the far field level 
will be proportional to the near-field level. Thus it is possible to correlate 
change in near field with the change in far field.

Neven
> 
> I fully agree with Ken. I have many times used house-made "sniffer" probes to 
> locate sources (and also coupling paths and/or antennas) of radiated 
> emissions. 
> They helped me identify and fix a number of compliance issues by pointing to 
> the 
> critical elements. 
> That is the real plus of these tools. On the other end, there is no point 
> trying 
> to correlate near and far-field readings.  
> 
> Regards,
> Paolo
> 
> 
> -Original Message-
> From: Ken Javor [mailto:ken.ja...@emccompliance.com] 
> Sent: Friday, November 22, 2002 12:24 AM
> To: Jim Bacher; Emc-Pstc (E-mail)
> Cc: 'tkrze...@genius.org.br'
> Subject: Re: EMC E&H close field probes / Mindcruiser
> 
> 
> 
> My opinion only, curious to see what others say.  The relationship between
> what is measured very close to a source and what is measured at three or ten
> meters depends very strongly on the efficiency of the radiating element.
> For example, if a chip by itself were radiating intensely close-in, you
> would get a very different 3 or 10 m signal than if the chip were connected
> to a long path on a PCB, and it would radiate still more if that path had a
> discontinuity in the ground plane beneath it (assuming a high enough
> frequency) and ground bounce then drove an externally connected cable.  So
> my opinion, for what it's worth, is that trying to correlate measured
> amplitudes close-in with 3 or 10 m signals is not practical in the general
> case of troubleshooting a test item.  The probe is useful for locating the
> source of an emission.
> 
> --
> >From: Jim Bacher 
> >To: "Emc-Pstc (E-mail)" 
> >Cc: "'tkrze...@genius.org.br'" 
> >Subject: FW: EMC E&H close field probes / Mindcruiser
> >Date: Thu, Nov 21, 2002, 3:46 PM
> >
> 
> >
> > Forwarding for Thomas Krzesaj, please copy Thomas when you respond.
> >
> > --
> > EMC E&H close field probes Message ID: 538546
> >
> > Hi,
> >
> > I would like to get more informations about close field probes and the
> > measurement methods.
> > What close field value can we consider as critical ?
> > How to interpret the result from the probe ?
> > We actually bought Agilent  11941A & 11940a probes and FischerCC E&H close
> > field probes.
> >
> >
> > My idea is to get an EMC-scanner like the DetectusAB one
> > (http://www.detectus.se/) to get more repeatibility. Can I get some advices?
> >
> > Thanks,
> > Thomas Krzesaj
> >
> > Genius Instituto de Tecnología
> > Av. Açaí, 875 Bloco E
> > 69075-904 Distrito Industrial
> > Manaus - Amazonas
> > Brasil
> >
> > Tel: +55 92 614-6578 / Fax: +55 92 613-3144
> > mailto:tkrze...@genius.org.br
> > http://www.thomask.fr.st
> > http://www.genius.org.br
> >Posted on Nov 20,2002 at 07:15am
> >
> >
> >
> >
> >
> >
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Re: Measuring inside a TEM cell

[neven11]

The usual parameters given with TEM cells are field uniformity and input 
impedance (or VSWR). Although they may appear to be very good up to the 
declared frequencies of operation, which depend on the transversal size of the 
cell, they are only good for empty cells. Presence of any conductor in the cell 
significantly reduces the upper frequency limit, by introducing strong 
resonances and/or change of propagation mode. Vendors usually won't tell you 
that. That is true even if the size is smaller than usually stated max useful 
dimansion of 1/3 of the height between the septum and the floor.

Measuring from the outside, say S11 or S21, will usually not show large change 
of reflection or transmission of the cell. However, you can easily see the 
peking of the field if you want to use the cell for calibrating a field probe. 
The probe will measure strong peaking (+ or -) of the field, depending on the 
relative orientation and size within the cell and type of the probe (E or H). 
I've extensively studied it as a part of a research project about ten years ago 
in Austrian Research Center Seibersdorf (the report might still be available 
somewhere there). This is the largest limitation on use of TEM cells.

Unless you have large mismatch of impedance at the tapered sections, which you 
can easily check with TDR (a network analyzer in TDR mode can also tell you 
that), I suspect that you see what I have described.

Neven
> 
> Hello all,
> 
> I have a problem regarding E and H field generation inside a TEM cell. I 
> have built a standard cell with Zw of 150 Ohms, which I need to generate 
> a known magnetic field strength around 90 MHz. The separation of the top 
> and bottom conductor is 25 cm, the overall length is about 130 cm.
> 
> But I don't get the expected results, only at lower frequencies up to 20 
> MHz the results are usable. At higher frequencies I suspect that I get a 
> standing wave inside my room, or that the cell dimensions in itself are 
> so large compared to the wavelength, that I get an unwanted resonance 
> inside the cell.
> 
> I have been looking for material about this in the 'net, but so far I 
> have not found pay dirt.
> 
> What am I missing here???
> 
> Greets
> Jochen Feldhaar
> Telejet GmbH
> 
> 
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Re: common mode immunity coupling units

[neven11]

Little belated response, but I thought it may be worth sending it anyway.

Laboratory Report: "Common-mode impedance measurements on cables in the 
frequency range 10-1000 MHz", report no. EIE 92004, by Mart Coenen from Philips 
in Eindhoven, the Netherlands, is probably the best reference on this subject.

If you connect a piece of long wire to a network analyzer, you can measure any 
impedance, from sub-Ohm to above kOhm. However, if you create the condition of 
cable-resonance, which is what the emission-testing is about when you maximize 
emission, then it can be shown that statistically the impedance is close to 150 
Ohm. The report describes a test results where a cable was set on a long bench 
over a plane, with an absorption clamp on it. One end of the cable was 
connected to a network analyzer (NWA). The clamp output was connected to the 
other NWA port and movedalong the cable to achieve max S21 (= max. emission 
condition). Then the input impedance of the cable was measured. All that was 
performed in many different configurations, and the measured impedances 
analyzed. The results support 150 Ohm as a reasonable "expected" value for the 
common-mode impedance of the cables.

BTW, if you look at the antenna theory, and realize that a cable in resonance 
is just a simple linear antenna such as monopole, half-wavelength or full-
wavelength dipole, then you'll see that its expected impedance at resonance is 
between about 30 Ohm and 300 Ohm, which again supports the 150 Ohm selection.

Neven


> 
> Please forgive my ignorance but can anyone tell me why above are designed to
> give load and source impedances of 150 ohms?
> 
> Cheers
> 
> Chris Colgan
> Compliance Engineer
> TAG McLaren Audio Ltd
> The Summit, Latham Road
> Huntingdon, Cambs, PE29 6ZU
> *Tel: +44 (0)1480 415 627
> *Fax: +44 (0)1480 52159
> * Mailto:chris.col...@tagmclaren.com
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> 
> 
> 
> 
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Re: Ethernet Radiated Emissions

[neven11]

> Pardon my naivety, but how does '100 Mbit' relate to 
frequencies of 30 and 60 kHz? Is this 100 Mbit per week? 
(;-)
> -- 
> Regards, John Woodgate, OOO - Own Opinions Only. 
http://www.jmwa.demon.co.uk 


First, a little background on auto negotiation. The IEEE 
802.3u 100BaseTX auto negotiation specification uses a 
modified version of the link integrity test defined for 
10BaseT devices. The link integrity test for 10BaseT 
devices uses the Normal Link Pulse (NLP), a burst pulse 
every 16 (+/- 8) microseconds. For 10/100 Mbps auto 
negotiation, a Fast Link Pulse (FLP) is used. The FLP 
includes the same NLP burst every 16 (+/- 8) msec for 
backward compatibility plus additional pulses every 62.5 
(+/- 7) microseconds. The FLP burst generates code words 
that are used for compatibility exchanges (duplex 
settings) between link partners. If a device (such as an 
Ethernet switch) sends FLP, but only receives NLP from 
it's link partner (such as a server or workstation), it 
will stop sending FLP and enable standard 10BaseT 
operation.

I suppose you can figure out that the frequency for 100 
Mbps link pulses is 62.5 kHz. If not, calculate 1/16 us.

Second, I recommend refraining from sarcastic comments 
in this forum, since that doesn't seem it was about 
naivety. I was actually trying to help.

Best regards, Neven


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Re: Ethernet Radiated Emissions

[neven11]

You are seing a spectrum of MLT3 signal, which is 100 
Mbit coding. Increased broadband emission is caused 
because some of the differential mode (DM) signal is 
either converted into common mode (CM) due to imbalance 
in the differential signalling or because you have some 
power/"ground" "noise", most likely power/"ground" 
bounce caused by the intentional signal over some common-
impedance (e.g. bonding "gnd" wire in a chip).

The parts of the story that have something to do with 
the first case are balance of the output driver 
(impedance and signal timing and slope), balance of the 
components/layout on the way of the signal to the 
Ethernet connetor, including the (im)balance in the 
pinout (1-2 vs. 3-6) if you are using regular and not 
integrated connectors (this happens even at the 
relatively low frequencies that you have problem with). 
Lack of good balance in the center-tap of the 
transformer may also significantly increase DM-CM 
conversion.

If you have "noisy" environment, where a part of the 
intentional signal is converted into (CM) noise on the 
power/"ground" structure, then it can increase the 
CM "driving" voltage (relative to the chassis 
i.e.enclosure) on the pairs. Center taps on both sides 
of the transfromer may be paths for CM noise to override 
the CM chokes and get on the UTP. Be careful with how 
and where you connect the center taps.

You may get some idea of what is happening if you 
can "force link", in which you activate the Tx without 
actually establishing link with the AUX equipment. Your 
SW guys should be able to help you with that. That will 
keep the Tx active regardless of what you connect. I can 
not help you with the details here, but I hope you can 
use this and think of some experiments you may perform 
to figure out what is causing the problems.

Good luck, Neven
> Hi Andy,
>  
> Most of the ports are linking to offsite support equipment or looped back to 
> get 
> link. The response seems consistent regardless of how it is linked. There is 
> also some tuning; broadband humps up a little higher in one spot or another 
> but 
> not a real big factor. I have tried 50 ft and shorter 3 to 10 ft on all 
> ports, 
> and tried ferrites on the offsite portions of the cables.
>  
> Using STP on the offsite portion of the cable will be an interesting test.
>  
> Thanks for the input.
>  
> Rick Linford
>  
>  
>  
>  
> -Original Message-
> From: Andy White (EWU) [mailto:andy.wh...@ewu.ericsson.se]
> Sent: Wednesday, October 09, 2002 3:39 PM
> To: Rick Linford
> Subject: RE: Ethernet Radiated Emissions
>  
> Hi Rick, 
> Is the problem only when you link more than 2 cables together? What is the 
> length of link cabling when adding cables? I susepect that the BB noise is 
> directly associated with the increased cabling and the lengths becoming 
> resonant.
> If cable lengths are the issue for the BB, the RE problem is not that easy to 
> resolve. Changing to another UTP will not really improve it, a section of STP 
> (on a link or some of the links) would probably help. I would give it a try. 
> Perhaps a cable ferrite may work on a link cable as well to reduce the BB 
> lump 
> amplitude. 100bT uses a 25MHz source so it may be possible to add some 
> filtering 
> at the pcb but this will probably affect the ENET operation/functionality.
> Hope you find a simple solution. 
> I liked your 'thanks to the marketing dept for the opportunity to learn' 
> comment 
> - classic :) 
> all the best 
> Andy 
>  
> Andy White, 
> Staff EMC Engineer 
> Ericsson Wireless Communications Inc. 
> San Diego, CA 92121 
> Tel 858 332 6214 / 877 877 7799 ext 26214 
> Fax 858 332 7311 
> e-mail andy.wh...@ewu.ericsson.se 
>  
> -Original Message- 
> From:   rlinf...@sonicwall.com [ mailto:rlinf...@sonicwall.com] 
> Sent:   Wednesday, October 09, 2002 1:55 PM 
> To: emc-p...@majordomo.ieee.org 
> Subject:Ethernet Radiated Emissions 
> Having worked on Ethernet (100 MB UTP) EMC for a few years, I now find myself 
> lacking understanding of Ethernet communications and how this may be 
> affecting 
> radiated emissions. 
> What is seen on the OATs is broadband noise between 50 and 150 MHz. With two 
> cables connected and linked, broadband is not even out of the noise floor. 
> With 
> the third and subsequent cables linked the broadband increases  With all 
> cables 
> attached and not linked there is no broadband. Reducing the resolution shows 
> peaks every 60 kHz. Probing on a linked signal shows peaks every 30 kHz  with 
> every other peak (60 kHz) being 20 dB higher. Probed several other types of 
> Ethernet equipment, NICs and switches and this seem consistent across all 
> products and manufactures. I feel the filters and layout is quite good, in 
> that, 
> with cables attached but no link there is no emission. In probing on the 
> board > it self the 30 kHz signature is present only o

Re: Filtering 100 BaseT during immunity

[neven11]

> >On the other (AUX) side of the transformers conect 
the center taps directly to the ground panel. You don't 
care about high-voltage isolation in this application, 
so you don't need any caps. 
> 
> How do you cope with ground potential differences, 
with centre-taps
> grounded at each end of the cable?
> -- 
> Regards, John Woodgate, OOO - Own Opinions Only. 

Center taps are not grounded on each end of the cable. I 
recommended adding transformer in-line, at the location 
of the feedthrough panel.

Each device (DUT and AUX) has a transformer and high-
voltage isolation in the front end. For RF coupled on 
the Ethernet line, which you want to filter out before 
it reaches the AUX equipment, the transformer you put in 
series with line effectively brings common-mode voltage 
on the cable to the voltage of the feedthtough panel 
(hopefully close to such low voltage that can not upset 
the AUX equipment). Additionaly, common-mode chokes in 
the part will further help reduce higher-frequency 
content that might go through due to any imbalance in 
the transformer center tap.

Neven


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Re: Filtering 100 BaseT during immunity

[neven11]

Using fiberoptic link is best if you can do it. However 
even so you need another end of the twisted-pair cable 
connected to another 100 Mbps device. You may check that 
device by looping it back on itself first and performing 
the immunity test on it. If it passes, it is safe to 
asume that it will not fail as supprt equipment to 
another DUT. Absorption clamp is an easy to use device 
too.

What I would recommend if you really want good 
decoupling of your AUX equipment is to use another set 
of Ethernet transformers in line with your cable. The 
transformers must have center taps in each pair, on both 
sides. I recomment GBit 1:1 transformers from BelFuse or 
Pulse. Insert transformers in line to each pair (used 
and unused), close to your AUX equipment, preferably at 
the chamber feedthrough panel. Place 75 Ohm resistor 
from each center-tap on the DUT-side to GND (chamber-
wall/panel) for common-mode termination. On the other 
(AUX) side of the transformers conect the center taps 
directly to the ground panel. You don't care about high-
voltage isolation in this application, so you don't need 
any caps. If you keep the connections from the center 
taps very short and low-inductance, this will be almost 
a bulletproff combination for protecting AUX equipment.

Some other additional measures come to mind, such as 
shielded cable on the AUX side and extra 10-15pF (max)
from each line to GND, but most likely you will never 
really need them.

All this said, there are many products on the market 
that meet 10V and 10 V/m, you can verify it with a pre-
test as I mentioned earlier, so I don't think you really 
need such a bulletproof combination. You can expect much 
more troubles with EFT and AUX equipment than with 
conducted or radiated RF.

Good luck, Neven
> 
> I want to provide isolation for auxillary equipment while performing
> radiated/conducted immunity testing on 100BT LAN. Tests are performed in a
> shielded room, and a bulkhead is used. Right now, cables pass right through
> the bulkhead (with, of course, split core ferrites of varying materials
> clamped to the cables on either side of the bulkhead). But this is not good
> enough.
> 
> Does anyone have an effective means of keeping the RF energy where it
> belongs (behind the bulkhead) ? By the way, this is low level testing, no
> more than 10V/m and 10 Vrms.
> 
> I have an option of using a fiber link (modem) through the bulkhead,
> however, I am not sure if this equipment will be susceptible, and no
> samples are available for test.
> 
> Thanks in advance.
> 
> Paul
> 
> 
> 
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Re: PCI Brackets Problems

[neven11]

Beware that stainless steel has high impedance in GHz 
range, about 50 times higher than copper. That seriously 
degrades performance at high frequencies relative to 
BeCu or other good conductors.

Neven
> 
> Rick,
> 
> Chomerics' Springline product line is an off-the-shelf solution:
> 
>   http://www.chomerics.com/products/cardcage.htm
> 
> The spring-fingers on these one-piece gaskets are formed
> toward the rear panel instead of toward the inside, where
> damage due to snagging can be a problem.
> 
> The only negative comment I have about this product concerns
> the stainless steel material. In my experience, mixing stainless steel
> and cold-rolled steel causes corrosion, even though the CRS is Zinc-plated.
> Chomerics has offered to tin-plate the SS for us.
> 
> Over the years, the design group I'm in has tried various
> custom gaskets for this application--strips of tin-plated Be/Cu 
> or Phosphor-Bronze spring fingers between the PCI brackets
> or fabric-over-foam gaskets, both of which have their
> challenges. It seems we've come full-circle and have settled
> on the above off-the-shelf solution.
> 
> Good Luck,
> Dan
> 
> > X-MimeOLE: Produced By Microsoft Exchange V6.0.5762.3
> > content-class: urn:content-classes:message
> > MIME-Version: 1.0
> > Subject: PCI Brackets Problems
> > Date: Fri, 30 Aug 2002 08:54:09 -0600
> > X-MS-Has-Attach: 
> > X-MS-TNEF-Correlator: 
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> > 
> > I am fighting the age old problem of PCI brackets on various PC chassis not 
> making adequate electrical contact. Aperture leaks, especially at high 
> frequencies, is a continual problem, to say nothing about the flimsy 
> construction of the brackets. Has anyone had any success with the clips, 
> gaskets 
> and other EMI solutions? If you have any suggestions on types, or 
> manufacturers 
> please let me know.
> > 
> > Thanks in advance...
> > 
> > Rick Busche
> > Evans & Sutherland
> > rbus...@es.com
> > 
> > ---
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RE: PCI Brackets Problems

[neven11]

Oooops,

my reply was really relevant to Compact PCI panels, not 
PCI. Sorry, I just realized it.

I haven't worked on designs using PCI brackets for EMC. 
I believe that former Instrument Specielties, now part 
of Laird Technologies, can help you. They are very 
knowledgeable in the area of shielding/gasketing, one of 
the best resources, and have many products for that.

Neven
> 
>   Yup, we had the same problem on a GNIC card. We made the card and its 
> L-shaped bracket. The card was intended for any ol' computer. The casual 
> contact 
> between the face of the bracket and the PC chassis was "iffy" at best. I put 
> a 
> couple of small dimples (punched slots really), on the long sides of the 
> bracket. They were on both sides of the bracket and spaced equidistant from 
> the 
> top and bottom of the opening in the PC's card mounting bracket. The dimples 
> made contact just before the end of the GNIC bracket aligned with the screw 
> hole 
> in the PC mounting bracket. This gave me enough force to make electrical 
> grounding contact, and effectively cut the card opening size by 1/3. Yes, it 
> does leave small slots between dimples, but these slots are significantly 
> smaller than the slots that are left unintentionally between the card and the 
> PC 
> mounting bracket. The GNIC, at the time, had a very noisy 1 X 9 laser 
> transceiver running at 1.25 GHz and this resolved my problem. The arrang!
> ement ended up being tested multiple times because of changes in 
> transceivers, 
> and other circuit changes but I never had any more problems with the fit.
> 
>   Gary
> 
> -Original Message-
> From: rbus...@es.com [mailto:rbus...@es.com]
> Sent: Friday, August 30, 2002 7:54 AM
> To: emc-p...@majordomo.ieee.org
> Subject: PCI Brackets Problems
> 
> 
> 
> I am fighting the age old problem of PCI brackets on various PC chassis not 
> making adequate electrical contact. Aperture leaks, especially at high 
> frequencies, is a continual problem, to say nothing about the flimsy 
> construction of the brackets. Has anyone had any success with the clips, 
> gaskets 
> and other EMI solutions? If you have any suggestions on types, or 
> manufacturers 
> please let me know.
> 
> Thanks in advance...
> 
> Rick Busche
> Evans & Sutherland
> rbus...@es.com
> 
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Re: PCI Brackets Problems

[neven11]

There are several types of gaskets. The ones with a 
continuous ridge along the centerline (inverted V-shape) 
are not compliant thus they can leave slots and cause 
difficulties with board insertion. The spiral gaskets 
make good contact but tend to kink, get caught and fall 
out of the groove in the panels.

The best ones have a series of rounded clip-
like "fingers" along the gasket, allowing each 
individual contact to comply with the size/shape between 
two panels. Regarding material, you want to use (plated) 
beryllium copper. I think the kind that is best is 
thermally treated after it has been formed.

Unfortunately the standard panels are aluminum, which is 
not best material regarding developing contact 
resistance to a different gasket material over time, due 
to galvanic effect/corrosion.

Neven
> 
> I am fighting the age old problem of PCI brackets on various PC chassis not 
> making adequate electrical contact. Aperture leaks, especially at high 
> frequencies, is a continual problem, to say nothing about the flimsy 
> construction of the brackets. Has anyone had any success with the clips, 
> gaskets 
> and other EMI solutions? If you have any suggestions on types, or 
> manufacturers 
> please let me know.
> 
> Thanks in advance...
> 
> Rick Busche
> Evans & Sutherland
> rbus...@es.com
> 
> ---
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Re: Designing for low power conducted and radiated immunity

[neven11]

Chris,

from what you described, it seems that a common-mode 
(CM) filter on all three lines would be a good approach. 
That will not reject your single-ended signal.

Coupled RF will mostly come as common-mode carried by 
the wire, thus that is what you want to reject in the 
first place. A good three-line CM choke, plus maybe some 
extra HF filters (e.g. caps/ferite beads in the signal 
line and between Vcc and GND) seems to be a way to go.

Neven 
> 
> Dear all,
> 
> On the evidence of the quality of responses I have seen on more difficult 
> queries, I think this should be fairly straightforward for all you RF 
> engineers
> out there.
> 
> My product is a small 3-wire pressure sensor which sends out a digital bit 
> stream encryption of the pressure measured. It's current draw is around 
> 30mA max. The bit stream is around 25kHz, 5V TTL. The 3-wires are 
> simply supply (5-10VDC), Output (5V logic) and Ground.
> 
> I am trying to make the product pass conducted RF immunity tests to
> EN 61000-4-6 (150kHz - 80Mhz) at 10V and radiated immunity tests to 
> EN 61000-4-3 (80Mhz - 1Ghz) at 30V/m. There is an intrinsic safety limit 
> on the overall capacitance I can use in the product.
> 
> My general thoughts are to use a PI-filter on each of the 3 lines with 
> the vertical section of the filter being ceramic capacitors to the metal
> case enclosure. A limit of about 10nF exists (for other reasons) on 
> these capacitors. 
> 
> The horizontal section of the PI will be made up of a series connection
> of a ferrite (for high frequency suppression) and an inductor for the lower
> frequencies where the ferrite is transparent - in that order. 
> 
> My problems (sorry .. challenges) are as follows:
> 
> 1 - I need to let a bit stream through at 25kHz, but reject RF at 150kHz
>  without a common mode choke (output is not differential). Is this a 
>  tall order?
> 
> 2 - The inductors that give me a reasonable value of impedance at these 
>  sub 1Mhz frequencies tend to be largish and have Self Resonant Freqs.
>  in the test spectrum albeit some of them (SRFs) are in the radiated 
> immunity 
>  band where I expect the ferrite to be in charge of attenuation. Is this
>  likely to cause me problems?
> 
> 3 - Can I find a single ferrite that will cover the entire RF test spectrum 
> of 
>  EN 61000-6-2 ( 150kHz - 1Ghz) or is it generally accepted that even the 
>  so called 'wideband' ferrites (SMT 0603/0805 max) are good down to  
>  about 5MHz but no lower?
> 
> Any relevant comments welcome.
> 
> Best regards
> 
> - Chris Chileshe
> - Ultronics Ltd
> 
> 
> 
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Re: Choce of Capacitance....

[neven11]

Using 1206 will force you to have (probably 
significantly) larger inductance than with 0805 or 0603. 
Inductance is the most important parameter above about a 
couple of MHz, because that will determine the 
decoupling impedance. Therefore you may decide to use 
all one value (except for the bulk caps) or to properly 
stagger the values of the caps (without creating 
parallel resonance, thus the values should not be far 
apart), but keep the inductance low. That criterion may 
force you to use smaller package than 1206. In addition, 
this will greatly depend on how you connect the caps, so 
keep low-inductance regardless of the cap size.

Neven
> Hi all,
> 
> I've just come from a discussion of decoupling capacitance 
> 
> In a nutshell, we have a combination of DSP and A-D/D-A conversion going on.. 
> I have recommended that we use a single 4.7 microfarad 1210 packaged cap in 
> place of the more traditional 0.1 and 0.001 microfarad 0805 caps in parallel. 
> I believe that the data shows a better compromise favoring the single chip. 
> Further, the need for BIG board entry caps is diminished.
> 
> This is on an 8 layer board.
> 
> Thoughts?
> 
> Thanks,
> 
> Derek Walton
> L F Research EMC Design and Test Facility

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Re: Screened vs. unscreened cable

[neven11]

Then it will work as an electrostatic (DC or low 
frequency electric field) shield. For all other 
prectical high frequency aplications you'll need it 
connected on both ends.

You can find good explanations, beyond this simple 
answer, in either Clayton Pauls's book "Introduction to 
Electromagnetic Compatibility" or Henry Otts's "Noise 
reduction Techniques in Electronic Systems"

Neven
> 
> Assume two separate units which is connected to each other via a screened
> cable. What happens if we remove the screen connection in one of the units ?
> will the cable function as an unscreened ?
> 
> Amund
> 
> 
> 
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Re: Meeting CISPR in Fast Ethernet board

[neven11]

Based on little info you have provided, I am making the 
following assumptions.
1) The noise is broadband noise coming from MLT3 signal 
(by "fast" you mean 100 Mbps?).
2) It is not from the power supplly, which can also 
radiate similarly looking noise in this portion of the 
spectrum.

You can find out easily if that is true if you switch to 
10 Mbps mode or even disconnect the other end of the UTP.

In that case, it is most likely that you may have 
chances fixing it by "playing" with the center-taps on 
the transformers (connect/disconnect etc.). I don't know 
anything about your layout or schematic, so try either 
side(s) of the transformer. Maybe you need to adjust the 
value of the center-tap cap. On the wire side you need 
to use high-voltage caps (if you are using them). This 
noise may be present on both Tx and Rx, so you might 
have to do it on both of them. You maybe have to spend 
some time figuring out if the levels on Tx and Rx are 
significantly different or not. The differential signals 
must be very symmetrical/balanced in layout too.

If the transceiver output stage is unbalanced quasi-
"differential" as some PHYs are, you may have hard time 
getting margin. You should be able to get it pass class 
A for e.g.24-port or class B for 1-2 port DUT, with UTP. 
You may have to ask your magnetics guys to tweak the 
part as well.

Cheers, Neven
> 
> Hi! I had a question regarding meeting EMI on my board
> for CISPR. I have a Fast Ethernet card and the 125MHz
> Fast Ehternet fails the CISPR in the 30Mhz to 100Mhz
> limit. 
> In the layout care has been taken to isolate the
> chassis or quiet ground from Digital ground by
> isolating the ground from the secondary of the
> magnetics to the connector where the cable gets
> connected.
> Does anybody have recommendations as to how should I
> improve the board to meet CISPR in 30Mhz to 100Mhz.
> Thanks
> Bob
> 
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Looking for EMC Design/SI/Compliance Job

[neven11]

Hello Group,

the private company I was with has laid off large number 
of people due to current market conditions, and I am in 
position to look for a job. I am located in SF Bay Area. 
Does anyone know of any opening that would match my 
experience, which is in the  EMC/SI and Compliance area. 

I pasted the summary of my qualifications below. For 
more information, I can be contacted offline. 

Thanks, Neven Pischl
npis...@yahoo.com


SUMMARY
MSEE with 15+ years of EMC and related experience. NARTE 
certified EMC-Engineer. Design for EMC and PCB-level SI, 
R&D in RF test and measurement methods, setup and manage 
EMC/Safety group and test facility, working with 
subcontractors and vendors, providing compliance test 
plans and working with external test houses. 

Experience with design for low-noise and high-immunity 
of various high speed (<100 ps) digital, analog, and RF 
products, and various LAN and WAN interfaces such as 
10/100/GBit Ethernet, xDSL, T1/E1, DS3, ISDN, FXS/FXO, 
IP Telephony/VoIP, OC12, wireless LAN and telephony. 
Worked in R&D, aerospace, consumer electronics, "low-
end" and "high-end" networking environments. Special 
interest and profound skills in EMC-design at all 
product-levels, with emphasis on PCB-level design.  
Provide detailed instructions for PCB, system, and 
mechanical design. Familiar  with various  
EMC/Safety/Telecom standards (e.g. EN55022/55024, CFR 47 
part 15, NEBS GR1089/63/78, ETSI 300386), how they apply 
to different products, certification process, and how to 
design to meet them.

Thorough knowledge of RF/MW concepts, theoretical and 
applied to high-speed digital design, such as 
transmission lines, signal-propagation and-termination, 
time-domain reflectometry (TDR), EM-field propagation, 
antennas, probes, transformers, EM-field and noise 
coupling, radiation mechanisms, power distribution and 
design of decoupling/bypassing, shielding and grounding. 
Use PSPICE, Hyperlynx, LINPAR, EZ-EMC for analysis, 
Allegro, Visula, and Mentor Graphics for PCB design 
reviews. Work with EMI-receiver/spectrum analyzer, 
network analyzer, TDR. Use bench test-methods and have 
designed test methodologies and probes for efficient 
troubleshooting.

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