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
[email protected] <mailto:[email protected]>
*From:* Brent DeWitt <[email protected]>
*Sent:* Tuesday, March 16, 2021 4:46 AM
*To:* [email protected]
*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: [email protected]
<mailto:[email protected]>
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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