Ken, do you notice much difference in emissions between 1 and 4 meters?
Bob Heller
3M EMC Laboratory, 76-1-01
St. Paul, MN 55107-1208
Tel: 651- 778-6336
Fax: 651-778-6252
=============================================================
Ken Wyatt
<ken@emc-seminars
.com> To
Sent by: Elliott Mac-FME001
[email protected] <[email protected]>
cc
[email protected]
04/13/2009 09:27 Subject
AM Re: [PSES] any recommendations on
floor absorber?
Hi Mac, et al,
At the Agilent - Colorado Springs test lab, we replaced our reflective
floor in the 3m chamber with the waffle tiles, covering it over with thin
plywood and carpeting. With the antenna / turntable angled from the center
line, we were able to achieve NSA without any trouble (30-1000 MHz). We
never measured above that, though, as we didn't have equipment standards
that required it. However, the comparison between 10m OATS and 3m FAC was
almost too good to be true. We were often within 2 dB and hardly ever more
than 4-5 dB different. This was data from real products with cables
attached and spread out, as well as comb generator data. ...and yes, I know
all the affects of near field versus far field and 3m versus 10m distance.
We were maybe just plain lucky, who knows? Bottom line is that the waffle
tiles did us GOOD!
Regards, Ken
Wyatt Technical Services, LLC
56 Aspen Dr.
Woodland Park, CO 80863
Email: [email protected]
Web: www.emc-seminars.com
(719) 310-5418
(888) 212-4602 toll-free
On Apr 10, 2009, at 10:51 PM, Elliott Mac-FME001 wrote:
Hi Charles - interesting question. I haven't really had any
experience with this.
Ferrite tiles become more reflective at higher frequencies so may be
unlikely to meet the criteria I would bet.
However, I have recently seen some "waffle" ferrite walls at a lab
recently that actually worked pretty well at not attenuating the
incident wave at higher freqs but instead "scattered" the reflections
and the dispersement seemed to work fairly well. Correlation to OATS
pretty good up to at least 8 GHz.
Whether or not it meets the CISPR site requirements would be a good
study....
Anybody out there have any luck using ferrite material
Best regards,
Mac Elliott
[ ] General Public
From: Grasso, Charles [mailto:[email protected]]
Sent: Friday, April 10, 2009 6:45 PM
To: Elliott Mac-FME001; Knighten, Jim L; [email protected]
Subject: RE: any recommendations on floor absorber?
Typically folks with chambers use tile – is that out of the question?
From: [email protected] [mailto:[email protected]] On Behalf Of
Elliott Mac-FME001
Sent: Friday, April 10, 2009 2:59 PM
To: Knighten, Jim L; [email protected]
Subject: RE: any recommendations on floor absorber?
Jim
Last year I started looking into this for my OATS as well but was
primarily looking at the upcoming changes to ANSI C63.4 [absorber
with > 20 dB attenuation over 1 GHz over freq range]. New version of
ANSI C63.4 will require 2.4m*2.4m square for 3m OATS and
proportionally higher for larger distances [about 8m*8m for 10m
site..]
I found two that meet the requirement, although I am sure there are
more out there
TDK Model IS-30A
ETS Lindgren Model EHP-12PCL
Both have distinct pros and cons.
The TDK seems like it would be better for anchoring down and leaving
on OATS due to closed cell absorber blended with polyethylene which
should be fairly impervious to elements [at least that is the theory]
The ETS comes in larger pieces and easier for transport but may not
be as resistant to elements.
Of course price comes into play as well....
I have done some experiments and found that NSA below 1 GHz seems to
be OK on 3m site except for 1-2 sites that are out. Could have been
operator error as we were doing yearly NSA tests and just stuck the
absorber out there to get general idea what would happen. No time to
investigate anomaly yet...
Am cautiously optimistic that NSA may be OK with absorber on ground
plane, which seems counter intuitive to me because I thought that the
ground bounce was included in the equation for ideal site
attenuation.
This doesn't seem to be the case for my 10m sites which are off axis
from the 3m site and we have dual masts for doing primarily Part 90
tests [TX], which won't require absorber and TIA 603 will actually
point to old ANSI standard which doesn't have it. There seems to be
an edge effect in VPOL if I leave the 3m foam down when I do my site
attenuation for my 10m sites. Need more investigation. Using the ANSI
C63.5:2006 AFs for NSA may help as well - need to do comparisons.
My hope is that my OATS with the absorber will meet the CISPR 16
[site requirements as well. May need some turntable treatment but
hopefully not as much of an issue as trying to meet it in a chamber
from what I have been hearing.
Anyway - more info than you probably needed but though I would share
with you and the rest of the group [especially since you have an
OATS].
Hope this helps [at least point towards some potential absorber!]
Best regards,
Mac Elliott
[ ] Motorola Confidential Restricted (MCR),
[ X ] Motorola Internal Use Only
[ ] General Public
From: [email protected] [mailto:[email protected]] On Behalf Of
Knighten, Jim L
Sent: Friday, April 10, 2009 1:57 PM
To: [email protected]
Subject: any recommendations on floor absorber?
I am looking for advice as I prepare for radiated emissions testing
above 1 GHz according to the CISPR test method, which becomes
mandatory in 2010.
I have an OATS with an all weather fiberglass dome (with a 4m
diameter turntable) in which I testensembles of floor-standing racks
of equipment (each rack ~6 ft high, 2000 lbs.)
Does anyone have recommendations to share with me as to candidate
absorber materials for placement on the floor to meet the CISPR
16-2-3 measurement method for measuring radiated emissions above 1
GHz?
I am guessing that important characteristics for absorbers may be:
fragility or durability, absorptionfrequency range, cost, and size.
I cannot easily raise my EUT to a height off the floor to clear the
absorbers, not can I configure my EUT to place certain chassis higher
or lower in the rack.
I appreciate your help in advance.
Jim
__________________________
James L. Knighten, Ph.D.
EMC Engineer
Teradata Corporation
17095 Via Del Campo
San Diego, CA 92127
858-485-2537 – phone
858-485-3788 – fax (unattended)
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