A screen room will be useful for conducted emissions but not radiated. Go
with the parking lot for radiated. It's cheaper and will yield better
results.
----------
From: [email protected] [SMTP:[email protected]]
Sent: Tuesday, April 27, 1999 5:00 PM
To: [email protected]
Subject: Re: Characterizing a screen room
On Tue, 27 Apr 1999 14:58:30 -0400, "WOODS, RICHARD"
<[email protected]>
wrote:
>You cannot perform a characterization that will mean anything. The
room will
>have standing waves that will be strongly dependant upon the size
and
>placement of the unit under test, the placement of the antenna and
the
>frequency.
That was the plan - record frequencies where the room is unreliable,
so we
don't spend time looking at that data. Real tests would be done at
an OATS.
My boss is interested in adding a screen room, but I'm worried that
resonances
will render the room worthless.
In light of that, do you think I'd be better off developing a
'parking lot
procedure', and figure out how to deal with the ambients?
>The best that you can do is perform a pretest to find the
>frequencies of interest then move to the OATS for a final test. A
screen
>room can be used for before and after comparison of EMI fixes, as
long as
>the unit under test is not moved. But once you have a fix, you will
still
>have to test on the OATS. Actually, you can perform diagnostic
tests in a
>lab if you set the antenna 1 m away. Just keep other sources a few
meters
>away from the antenna.
>
>To do what you want to do, you will need a compact semi-anechoic
chamber at
>a cost of about $140, 000 including the turn table. We just started
using
>one that complies with the NSA test given the constrant that we
can't run
>the antenna up to 4 m. We have found up to 6 dB of variation
between the
>chamber and the OATS. However the variation is small enough that
we pretest
>and fix in the chamber and only move to the OATS once we have
confidence
>that we have at least 6 dB of margin. So far so good, but I don't
doubt that
>some day we will end up out of compliance at the OATS even with 6
dB of
>margin in the chamber.
>
> ----------
> From: [email protected] [SMTP:[email protected]]
> Sent: Tuesday, April 27, 1999 12:22 PM
> To: [email protected]
> Subject: Characterizing a screen room
>
> My company is planning to purchase a screen room for
radiated
>emissions
> precompliance testing.
>
> I'm aware that reflections can cause resonances and
drastically
>influence
> readings. What kind of testing could I do to characterize
the room
>(aside from
> simple experience)?
>
> --
> Patrick Lawler
> [email protected]
>
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--
Patrick Lawler
[email protected]
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