Barry,
I'm guessing that part of the reason are the complex geometries that
can be generated in rooms with reflections etc - even using the abosrbers.
So small changes in equipment arrangement can throw things way off. Meaning
that you can't rely on the repeatibility of the "correction factor" you
develop between room and OATS.I also have a hunch that the issue is complex
enough that they didn't really want to evaluate it a whole lot because there
was already a solution at hand - the OATS facility. I'm not trying to
beat-up on the committees in this case, just that they had other items to
think about which they felt were more important.
I have used small chamber like you describe quite effectively as a
screening tool, but you just had to learn you chamber. We worked on the
equipment inside the chamber until out experience between that and our OATS
told us we were probably ready to test in the open field. I was successfull
with that approach about 90% of the time. I could really say by what margin
the product was likely to pass, I could just tell them that we had a really
good probablity of passing - and again with experience it allowed the
non-correlatable chamber to be a very good precursor to successful oats
testing. (I wouldn't try this in a non-lined chamber however - there is just
way to much variablity in that)
Probably 2 cents to much
Gary
-----Original Message-----
From: Barry Ma [mailto:[email protected]]
Sent: Tuesday, January 11, 2000 2:55 PM
To: [email protected]
Cc: [email protected]
Subject: RE: Chamber and OATS Coorelat
Mirko,
I happen to have a copy of CISPR 16-1 at hand. Clause 16.6 "Open area site
validation procedure" reads:
... The deviation between a measured NSA value and the theoretical value
shall not be used as a correction for a measured EUT field strength. This
procedure shall be used only for validating a test site. ...
The above statement is not followed by any explanation. What do you think
the reason is? My guess is that there are lot of factors causing inaccurate
E-field measurement. The collective result of those factors cannot be simply
corrected by changing antenna factors.
At the end of your message, however, you stressed on "for a specific test
setup". May we try this "illegal" correction procedure with caution only
"for a specific test setup" and for a specific frequency range? Hopefully it
might be worthwhile to try.
Barry Ma
Anritsu Company
Morgan Hill, CA
-----------
On Tue, 11 January 2000, "Matejic, Mirko" wrote:
Richard,
You could improve correlation by adjusting chamber antenna factors for a
correlation differences which you can get from NSA measurements one at OATS
the other in the chamber with a fixed antenna height. You could also
determine correlation differences by comparing measured field strength
levels from battery powered comb generator.
Fixed vs. 1-4m antenna height among other factors will always create
unpredictable correlation for a specific test setup.
Mirko Matejic
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