RE: Shielded Room

[Chris Chileshe]

Hi Jim,

Try  http://www.emctest.com/

The standards will depend on what needs to be tested in the room as
the field strengths, absorber materials, types of antennae and physical
size if the EUT all have a part to play.

Regards

- Chris Chileshe
- Ultronics Ltd
- Cheltenham, UK


-Original Message-
From:   Jim Bacher [SMTP:jim_bac...@mail.monarch.com]
Sent:   Thursday, February 15, 2001 3:31 PM
To: Acon Harsono; emc-p...@majordomo.ieee.org
Cc: davehe...@mediaone.net
Subject:Re:Shielded Room


forwarding for a_hars...@telkom.net

Reply Separator
Subject:Shielded Room
Author: "Acon Harsono" 
List-Post: emc-pstc@listserv.ieee.org
Date:   2/15/01 6:46 PM

Hello All,

I am studying the Shielded Room for Conducted RFI testing.
Can anybody tell me the technical requirements or standards for the shielded
room ?

Thank you,


Acon Harsono
SUCOFINDO Laboratory - Indonesia
Tlp.:   +62 21 88321176 ext. 1862
Fax.:  +62 21 88321166
email: a_hars...@telkom.net


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RE: Shielded Room

[Jim Eichner]

Doing radiated emissions measurements using an actual antenna is of course
subject to all sorts of inaccuracies due to room reflections and nulls.  In
our engineering mitigation efforts though, we don't use an antenna - instead
we use clamp-on RF current probes on our cables.  In equipment with a
well-designed enclosure, the radiated emissions will all be due to (mostly
common-mode) currents on cables, and we've found this method to work quite
well for mitigation.

We are planning on moving that mitigation lab from an ordinary meeting room
into a shielded room,  basically because one is available in the building
we're moving into.  We will also have an anechoic chamber, so perhaps I can
find the time to run some comparison tests, but in the meantime, I'm curious
whether people think reflections and nulls in the shielded room will
influence our current probe readings, and if so, what the extent might be
and what the mechanism might be.

The same question applies to LISN measurements:  will we be worse off in a
shielded room?

Thanks for your input,

Jim Eichner
Sr. Regulatory Compliance Engineer
Mobile Markets
Xantrex Technology Inc.
Email: jim.eich...@xantrex.com
Website: www.xantrex.com
Any opinions expressed are those of my invisible friend, who really exists.
Honest.



-Original Message-
From: Jim Hulbert [mailto:hulbe...@pb.com]
Sent: Friday, December 15, 2000 7:09 AM
To: Gorodetsky, Vitaly
Cc: emc-p...@majordomo.ieee.org
Subject: Re: Shielded Room





You should never use an un-lined shielded room for either radiated emissions
or
radiated susceptibility tests, even on a preliminary basis.  The reflections
of
the RF signals off the walls, floor and ceiling cause errors of 20dB or
more.
Nulls will hide certain signals and resonances will amplify others randomly
and
unpredictably.You can see the strong effect of nulls and resonances by
just
slightly moving either the equipment you are testing or the antenna.   You
will
never get any sort of meaningful test data.   Lining the 4 walls and ceiling
of
the chamber with ferrite absorbing material is absolutely necessarily if you
want to have any confidence at all in radiated test results.





"Gorodetsky, Vitaly"  on 12/14/2000 03:05:38 PM

Please respond to "Gorodetsky, Vitaly" 

To:   "Emc-Pstc (E-mail)" 
cc:(bcc: Jim Hulbert/MSD/US/PBI)

Subject:  Shielded Room




Dear Colleagues,

I have been asked to comment on the scope of use/capabilities of shielded
rooms (2-3m x 2m).  I would appreciate if you would share your opinion on
the usefulness of Radiated Emissions tests, validity of data, effectiveness
of establishing an emissions baseline information of approved products for
future design changes.  Any recommendations for improving the usefulness?
Please do not limit yourself to the above and feel free to expand.

Any comments, advice will be greatly appreciated.

Vitaly  Gorodetsky
Compliance Engineer   Direct:(818) 678-3840
Canoga Perkins Corp.   Main:  (818) 718-6300
20600 Prairie Street   FAX:  (818) 678-3740
Chatsworth, CA 91311-6008  e-mail:
vgorodet...@canoga.com <mailto:vgorodet...@canoga.com>

The suitability of this information for making decision is solely with the
reader


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Re: Shielded Room

[Cortland Richmond]

I have used and built such a room. It IS useful, An experienced engineer or
technician will be able to make surprisingly accurate guesses about what a
new EUT will do when outside of the shielded room. But you will have to
accept that they will ONLY be guesses.

Back in the FCC Class B certification days, I assembled a room in Fort
Worth about 3 by 4 meters, by splicing two old Lindgren chambers together.
We also had a regular Ray-Proof 3 meter square chamber, and added a chamber
about 3 by 6 meters later. (That one needed some anechoic material to be
made equivalent to the others.) In each of these, we were able to test
small equipment - desktop and laptop computers -- at one meter. We did so
by adopting a strict 10 dB margin. This enabled us to almost always come in
under the limit when we sent equipment out for the OATS tests the FCC
certification process required. Some adjustment was needed in order to fine
tune those results, but I look back with surprise at how well we did.

The key was experience.  The head of the shop there was an older engineer
in his 60's who could run a 141T in his sleep - and we had one. I'd been in
the Signal Corps 20 years, had been a Ham 30, and had five years experience
doing FCC and TEMPEST testing myself.  Later equipment upgrades allowed
newer engineers to slot right in. And we had a tech who was a GENIUS at
maximizing; he could add 10 dB and stay within MP4.

Limitations? Sure. I would not want to test anything bigger than tabletop. 
Coax placement as well as EUT leads was critical. We had to strenuously
avoid symmetry in the chamber; no need to excite more resonance modes that
we had to. We rotated equipment by had while  testing, probably
mode-stirring and smoothing things out.  And we learned to avoid doing
certain conducted tests in the chamber, as those same resonance modes could
artificially raise conducted emissions readings.

Yes, you can use them. Just be very, very careful.

Cheers,

Cortland

== Original Message Follows 
From: "Gorodetsky, Vitaly" 
Subject: Shielded Room
List-Post: emc-pstc@listserv.ieee.org
Date: Thu, 14 Dec 2000 12:05:38 -0800
Reply-To: "Gorodetsky, Vitaly" 


Dear Colleagues,

I have been asked to comment on the scope of use/capabilities of shielded
rooms (2-3m x 2m).  I would appreciate if you would share your opinion on
the usefulness of Radiated Emissions tests, validity of data, effectiveness
of establishing an emissions baseline information of approved products for
future design changes.  Any recommendations for improving the usefulness?

Please do not limit yourself to the above and feel free to expand.

Any comments, advice will be greatly appreciated.
 
Vitaly  Gorodetsky
Compliance Engineer Direct: (818) 678-3840
Canoga Perkins Corp.Main:   (818) 718-6300
20600 Prairie StreetFAX:(818) 678-3740
Chatsworth, CA 91311-6008   e-mail:
vgorodet...@canoga.com   


== End of Original Message =

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Re: Shielded Room

[Jim Hulbert]

You should never use an un-lined shielded room for either radiated emissions or
radiated susceptibility tests, even on a preliminary basis.  The reflections of
the RF signals off the walls, floor and ceiling cause errors of 20dB or more.
Nulls will hide certain signals and resonances will amplify others randomly and
unpredictably.You can see the strong effect of nulls and resonances by just
slightly moving either the equipment you are testing or the antenna.   You will
never get any sort of meaningful test data.   Lining the 4 walls and ceiling of
the chamber with ferrite absorbing material is absolutely necessarily if you
want to have any confidence at all in radiated test results.





"Gorodetsky, Vitaly"  on 12/14/2000 03:05:38 PM

Please respond to "Gorodetsky, Vitaly" 

To:   "Emc-Pstc (E-mail)" 
cc:(bcc: Jim Hulbert/MSD/US/PBI)

Subject:  Shielded Room




Dear Colleagues,

I have been asked to comment on the scope of use/capabilities of shielded
rooms (2-3m x 2m).  I would appreciate if you would share your opinion on
the usefulness of Radiated Emissions tests, validity of data, effectiveness
of establishing an emissions baseline information of approved products for
future design changes.  Any recommendations for improving the usefulness?
Please do not limit yourself to the above and feel free to expand.

Any comments, advice will be greatly appreciated.

Vitaly  Gorodetsky
Compliance Engineer   Direct:(818) 678-3840
Canoga Perkins Corp.   Main:  (818) 718-6300
20600 Prairie Street   FAX:  (818) 678-3740
Chatsworth, CA 91311-6008  e-mail:
vgorodet...@canoga.com 

The suitability of this information for making decision is solely with the
reader


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RE: Shielded Room

[UMBDENSTOCK]

Hello Vitaly,

I found it more useful to use the OATS for initial measurements with the
measurement antenna spaced at a close distance to the EUT than to use the
shielded room for ballpark measurements.  The reflections in the shielded
room caused too much of a variation in the emissions to guess which
emissions to evaluate and which ones could be skipped.  

Once a base line is established on the OATS, the shielded room can be useful
for a - b comparisons.  This way you can see the profile of the product
without the camouflage of the ambients and see at a glance if any other
emissions popped up when you beat down the emission of interest.

We were fortunate enough to justify a ferrite lined compact chamber for
immunity work.  This chamber gets used about 90% of the time for
precompliance emissions work prior to going to the OATS, even though it was
justified for immunity.  We really get our money's worth.  The reflections
are much less than a shielded room and ballpark results for initial
measurements can be observed.

Good luck,

Don Umbdenstock
Sensormatic

> --
> From: Gorodetsky, Vitaly[SMTP:vgorodet...@canoga.com]
> Reply To: Gorodetsky, Vitaly
> Sent: Thursday, December 14, 2000 3:05 PM
> To:   Emc-Pstc (E-mail)
> Subject:  Shielded Room
> 
> 
> Dear Colleagues,
> 
> I have been asked to comment on the scope of use/capabilities of shielded
> rooms (2-3m x 2m).  I would appreciate if you would share your opinion on
> the usefulness of Radiated Emissions tests, validity of data,
> effectiveness
> of establishing an emissions baseline information of approved products for
> future design changes.  Any recommendations for improving the usefulness?
> Please do not limit yourself to the above and feel free to expand.
> 
> Any comments, advice will be greatly appreciated.
>  
> Vitaly  Gorodetsky
> Compliance Engineer   Direct: (818) 678-3840
> Canoga Perkins Corp.  Main:   (818) 718-6300
> 20600 Prairie Street  FAX:(818) 678-3740
> Chatsworth, CA 91311-6008 e-mail:
> vgorodet...@canoga.com 
> 
> The suitability of this information for making decision is solely with the
> reader
> 
> 
> ---
> This message is from the IEEE EMC Society Product Safety
> Technical Committee emc-pstc discussion list.
> 
> To cancel your subscription, send mail to:
>  majord...@ieee.org
> with the single line:
>  unsubscribe emc-pstc
> 
> For help, send mail to the list administrators:
>  Jim Bacher:  jim_bac...@mail.monarch.com
>  Michael Garretson:pstc_ad...@garretson.org
> 
> For policy questions, send mail to:
>  Richard Nute:   ri...@ieee.org
> 
> 

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