Mike and others,
EN 55022:1994/A2:1997 (CISPR 22:1993/A2:1996 Modified) contains
guidelines for site attenuation measurements of alternative sites in
normative Annex A. These measurements are volumetric measurements
which seem to follow the ANSI C63.4 volumetric measurements required
for alternative sites.
Interestingly, I don't see any definition of "alternative test sites"
in CISPR 22 or CISPR 16. However, under the ANSI C63.4 definition,
alternative test sites are essentially all sites other than true "open
area test sites". A site that is weather protected but otherwise
"open area" is considered an alternative site under ANSI C63.4, as
well as more obvious alternative sites such as anechoic chambers and
factory sites. It seems to me that for practical reasons, true open
area test sites under ANSI C63.4 are mostly limited to sites in warm
dry climates where weather is not a major factor and weather
protection is not needed.
Under ANSI C63.4, alternative sites generally must meet volumetric
site attenuation criteria. "Weather protected test sites" are
currently exempt from this requirement (perhaps due to industry
pressure?) but the requirement is under consideration.
If and when volumetric site attenuation measurements must be
universally met, I wonder how many previously acceptable sites will
have to be abandoned or rebuilt.
Jim Hulbert
Senior Engineer - EMC
Pitney Bowes
______________________________ Forward Header __________________________________
Subject: Re: ANSI C63.4
Author: "Mike Fahrion" <[email protected]> at SMTPGWY
List-Post: [email protected]
Date: 11/13/98 9:48 AM
We have a second story, weather protected 3m site. Ground plane measures
6.1m x 7.3m. NSA measurements always were close to the 4 dB limit at 30MHz
in horizontal polarization, all higher frequencies had no problems in
vertical or horizontal polarizations. The 30MHz trouble was attributed to
marginal ground plane area.
However - when we started using the volumetric method of SA measurements
problems were found. Using this method, the antenna is moved to various
locations encompassed by the swept volume of the EUT when rotated on the
turntable. This brought our antenna (now broadband instead of dipole) much
closer to the edges of the ground plane. Note the discontinuity at the
edges of our ground plane were huge since it was about 3 meters above
ground/earth level.
This led to a current, expensive project of constructing a new weather
protected OATs. New ground plane dimensions are 9.75m x 17m. I have hopes of
this site meeting NSA at both 3m and 10m. This is still much smaller than 17
x 20m dimension recommended by someone else here, but exceeds the freznel
ellipse and is much bigger than listed in CISPR16 (although CISPR doesn't to
my knowledge call for volumetric testing, which seems more stringent).
The new site ground plane will be within 4 inches of ground level. I don't
plan to try to bond the interior ground plane to earth unless there is
trouble meeting NSA.
I will know the outcome of this project in 4-6 weeks. For the $ involved, it
had better be successful!
Best Regards,
Mike Fahrion
[email protected]
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