Hi Mac,
Per CISPR 22, emission measurements above 1GHz are done at a 3 meter test
distance, even on a 10 meter site. Doesn't this mean that the same amount of
absorber would be used on a 3 meter or 10 meter site since the test distance
is 3 meters?
Even if the NSA below 1GHz is passing, I believe the absorber material would
need to be removed when performing measurements below 1GHz.
Thanks,
Tim
In a message dated 6/16/2009 7:15:39 AM Pacific Daylight Time,
[email protected] writes:
Hey Tim / group
I don't know whether or not this would meet the CISPR requirements but
may be
a place to start.
The proposed ANSI C63.4 revision [that I saw last year] requires
meeting the
CISPR 16-1-4 requirements or alternately using absorber that is at least 20 dB
down for freqs over 1 GHz [not sure what the upper range is off hand].
The requirements is a 2.4m * 2.4m for 3m OATS and proportionally larger
for
larger sites - which for a 10m site comes out to 8m*8m - quite a large
footprint.
There are companies out there that state that their absorber that meets
these
criteria will be weather [rain and sun] resistant and should retain their
electrical characteristics for 5 years or maore - but they are quite expensive
- especially for a 10m site.... This company has plastic anchors that you can
attach to your ground plane to keep the absorber in place.
I have done some preliminary experimentation on my 3m site with the
absorber
and it seems that - except for a few points - NSA comes in under 1GHz with the
absorber down. May even improve. Challenged my thinking on the perfect site
model and NSA curves because I thought a perfect reflection was included. Was
told this would be the case but needed to see it myself. I want to repeat the
tests using only ANSI C63.5 2006 antenna factors and see how it works out -
maybe those few troublesome spots will come in. [if I can get site time for
experimentation!.]. Would like to do these tests before the Symposium
hopefully.
Maybe an OATS that has a significant OFA with these absorbers would
meet the
CISPR requirements. If the experimentation I describe above is favorable I
plan to try that as a next step and will keep the forum posted .
If anyone can think of reasons that the solution above could not meet
the
CISPR requirements would like to hear them as well.
Anyway, hope this helps
Best regards,
Mac Elliott
[ ] General Public
________________________________
From: [email protected] [mailto:[email protected]] On Behalf Of
[email protected]
Sent: Monday, June 15, 2009 7:49 PM
To: [email protected]
Subject: CISPR22:2005 + A1:2005
Hello Group,
I have a question on the new CISPR22 ammendment that becomes effective
10-2010. It requires free space emission measurements above 1GHz. This is
typically done with ferrite absorber on the chamber floor.
How does one address this issue when testing on a 10 meter OATS? Are
there
any site modifications needed? The OATS uses a mesh (chicken wire) for the
ground plane instead of solid metal panels.
Please also advise if there is any new site validation requirements to
do
testing above 1GHz. In the past, if NSA is passing below 1GHz, the site would
be valid for testing above 1GHz.
Thanks,
Tim Pierce
TAP Engineering & Associates
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