Re: [PSES] RF absorber for EMC room

2021-03-18 Thread Cortland Richmond 
 When I retired from the Army in 1983, I found employment as a test 
engineer (sans diploma) at Wang Labs FCC/TEMPEST test lab, with IIRC 
8-foot-long axial walls and half that on the ceiling and sides.


The TEMPEST computers were often  larger than a VW bug.


Cortland Richmond
Last employment contract eng. at Belcan


On 3/17/2021 6:17 PM, Ghery S. Pettit wrote:


I will agree with Brent completely on this.  Prior to retiring I’ve 
had chambers built both ways. Carbon loaded pyramidal foam absorbers 
are big.  The chamber I had built for Tandem Computers in 1989 had 
cones that were 8 feet tip to base.  The chambers I had built for 
Intel Corporation back in 1995/6 used hybrid absorbers.  Ferrite tiles 
for the lower end of the spectrum, cones at the higher end.  Like 
Brent, I haven’t seen pure cones used in years. They require a larger 
envelope for the chamber and add cost to the project.  If you are 
retrofitting and existing chamber the hybrid approach becomes all the 
more critical.


I can’t speak to the potential for migration of the fire retardant 
salts in cones, but from what I remember hearing decades ago a fire in 
absorbers is not something that you want to experience, so a fire 
suppression system is imperative.


Ghery S. Pettit

Pettit EMC Consulting LLC

gh...@pettitemcconsulting.com <mailto:gh...@pettitemcconsulting.com>

*From:* Brent DeWitt 
*Sent:* Tuesday, March 16, 2021 4:46 AM
*To:* EMC-PSTC@LISTSERV.IEEE.ORG
*Subject:* Re: [PSES] RF absorber for EMC room

Yes, but.

To be effective down to 30 MHz, "classic" carbon loaded, tapered foam 
absorbers need to be huge, on the order of 2 meters high.  That eats a 
lot of internal chamber volume.  I'm also not sure if anyone makes 
them currently.  Also, do _not_ buy old (10 year +), used absorbers!  
They still work fine as absorbers, but tend to lose there 
self-extinguishing capability due to the migration of the retardant 
salts used in the manufacturing process for that purpose.  Urethane 
fires are not something you want to experience.


Respectfully,

Brent DeWitt
iRobot
Bedford, MA

On 3/16/2021 5:13 AM, McBurney, Ian wrote:

A question for the EMC experts.

Is there an alternative rf absorber to ferrite tiles that works
between 30MHz to 1GHz? I am thinking of the pyramidal type absorber.

This is for research for partially lining a pre compliance
radiated rf emission EMC room.

Many thanks in advance.

Ian McBurney

Lead Compliance Engineer.

Allen & Heath Ltd.

Kernick Industrial Estate,

Penryn,

Cornwall. UK.

TR10 9LU.

Tel: 01326 370121

Email: ian.mcbur...@allen-heath.com
<mailto:ian.mcbur...@allen-heath.com>

Allen & Heath Ltd is a registered business in England and Wales,
Company number: 4163451. Any views expressed in this email are
those of the individual and not necessarily those of the company. -


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Re: [PSES] RF absorber for EMC room

2021-03-17 Thread Ghery S. Pettit 
I will agree with Brent completely on this.  Prior to retiring I've had
chambers built both ways.  Carbon loaded pyramidal foam absorbers are big.
The chamber I had built for Tandem Computers in 1989 had cones that were 8
feet tip to base.  The chambers I had built for Intel Corporation back in
1995/6 used hybrid absorbers.  Ferrite tiles for the lower end of the
spectrum, cones at the higher end.  Like Brent, I haven't seen pure cones
used in years.  They require a larger envelope for the chamber and add cost
to the project.  If you are retrofitting and existing chamber the hybrid
approach becomes all the more critical.

 

I can't speak to the potential for migration of the fire retardant salts in
cones, but from what I remember hearing decades ago a fire in absorbers is
not something that you want to experience, so a fire suppression system is
imperative.

 

Ghery S. Pettit

Pettit EMC Consulting LLC

gh...@pettitemcconsulting.com <mailto:gh...@pettitemcconsulting.com> 

 

 

From: Brent DeWitt  
Sent: Tuesday, March 16, 2021 4:46 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] RF absorber for EMC room

 

Yes, but.

To be effective down to 30 MHz, "classic" carbon loaded, tapered foam
absorbers need to be huge, on the order of 2 meters high.  That eats a lot
of internal chamber volume.  I'm also not sure if anyone makes them
currently.  Also, do _not_ buy old (10 year +), used absorbers!  They still
work fine as absorbers, but tend to lose there self-extinguishing capability
due to the migration of the retardant salts used in the manufacturing
process for that purpose.  Urethane fires are not something you want to
experience.

Respectfully,

Brent DeWitt
iRobot
Bedford, MA

On 3/16/2021 5:13 AM, McBurney, Ian wrote:

A question for the EMC experts.

 

Is there an alternative rf absorber to ferrite tiles that works between
30MHz to 1GHz? I am thinking of the pyramidal type absorber.

This is for research for partially lining a pre compliance radiated rf
emission EMC room.

 

Many thanks in advance.

 

Ian McBurney

Lead Compliance Engineer.

Allen & Heath Ltd.

Kernick Industrial Estate,

Penryn,

Cornwall. UK.

TR10 9LU.

Tel: 01326 370121

Email: ian.mcbur...@allen-heath.com <mailto:ian.mcbur...@allen-heath.com> 

 

Allen & Heath Ltd is a registered business in England and Wales, Company
number: 4163451. Any views expressed in this email are those of the
individual and not necessarily those of the company. -


This message is from the IEEE Product Safety Engineering Society emc-pstc
discussion list. To post a message to the list, send your e-mail to
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Re: [PSES] RF absorber for EMC room

2021-03-16 Thread Brent DeWitt 

Yes, but.

To be effective down to 30 MHz, "classic" carbon loaded, tapered foam 
absorbers need to be huge, on the order of 2 meters high.  That eats a 
lot of internal chamber volume.  I'm also not sure if anyone makes them 
currently.  Also, do _not_ buy old (10 year +), used absorbers!  They 
still work fine as absorbers, but tend to lose there self-extinguishing 
capability due to the migration of the retardant salts used in the 
manufacturing process for that purpose. Urethane fires are not something 
you want to experience.


Respectfully,

Brent DeWitt
iRobot
Bedford, MA

On 3/16/2021 5:13 AM, McBurney, Ian wrote:


A question for the EMC experts.

Is there an alternative rf absorber to ferrite tiles that works 
between 30MHz to 1GHz? I am thinking of the pyramidal type absorber.


This is for research for partially lining a pre compliance radiated rf 
emission EMC room.


Many thanks in advance.

Ian McBurney

Lead Compliance Engineer.

Allen & Heath Ltd.

Kernick Industrial Estate,

Penryn,

Cornwall. UK.

TR10 9LU.

Tel: 01326 370121

Email: ian.mcbur...@allen-heath.com

Allen & Heath Ltd is a registered business in England and Wales, 
Company number: 4163451. Any views expressed in this email are those 
of the individual and not necessarily those of the company. -



This message is from the IEEE Product Safety Engineering Society 
emc-pstc discussion list. To post a message to the list, send your 
e-mail to mailto:emc-p...@ieee.org>>


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http://www.ieee-pses.org/emc-pstc.html 



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site at http://product-compliance.oc.ieee.org/ 
 can be used for graphics (in 
well-used formats), large files, etc.


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[PSES] RF absorber for EMC room

2021-03-16 Thread McBurney, Ian 
A question for the EMC experts.

Is there an alternative rf absorber to ferrite tiles that works between 30MHz 
to 1GHz? I am thinking of the pyramidal type absorber.
This is for research for partially lining a pre compliance radiated rf emission 
EMC room.

Many thanks in advance.

Ian McBurney
Lead Compliance Engineer.
Allen & Heath Ltd.
Kernick Industrial Estate,
Penryn,
Cornwall. UK.
TR10 9LU.
Tel: 01326 370121
Email: ian.mcbur...@allen-heath.com

Allen & Heath Ltd is a registered business in England and Wales, Company 
number: 4163451. Any views expressed in this email are those of the individual 
and not necessarily those of the company.

-

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discussion list. To post a message to the list, send your e-mail to 


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