I have no personal experience with raised sites, but I do know of folks that
skimped on the size of their ground planes when they were on the surface,
and they could not pass. I made my comments based upon that input and the
following.
According to C63.7 Section 6.1, " . . . it may be prudent to have the
capability to extend the rectangular or trapezoidal dimensions of the ground
plane up to or larger than the dimensions of the Fresnel ellipse. This is
especially important for ground planes that are elevated above the
surrounding surfaces."
----------
From: [email protected] [SMTP:[email protected]]
Sent: Thursday, November 12, 1998 11:06 AM
To: [email protected]
Subject: RE: ANSI C63.4
Hi Richard,
Would you please explain in detail what you said "Raising your
ground plane
above ground level is not recommended as it tends to create ground
discontinuities at the edge of the plane." in the 2nd paragraph of
your
following article. To my limited knowledge, people don't have
problem with
OATS atop their buildings.
It seems to me that the discontinuities at the edge of the plane
exist on
every OATS, including those on a level with ground. ANSI C63.7
already
considers it. The OATS with ground plane above ground level is not
an
exception of the consideration.
Thank you.
Best Regards,
Barry Ma
-------------
Original Text
From: "WOODS, RICHARD" <[email protected]>, on 11/11/98 1:21 PM:
Consult C63.7, "Guide for Construction of Open-Area Test Sites. We
built
our
site according to the guidelines with two exceptions: we soldered
the
ground
plane sections at about 6 inches and we made the plane size slightly
larger
than the recommendations. We passed the first time. I recommend the
increased size.
Raising your ground plane above ground level is not recommended as
it tends
to create ground discontinuities at the edge of the plane. For
example,
this
can be a problem for OATS on top of buildings. This problem can be
corrected
by increasing the size of the plane.
We run our cables over the ground plane and do not have a problem.
Our OATS is in on the edge of a woods with trees on two sides and
water on
two sides. On the water sides, we have bushes to "hide" the site
(required
by the building code). We have not noticed a problem.
Re how far way an object must be: I saw a film produced by HP where
they
had
a metal fence far outside the ellipse. They claimed that they could
see
variations in the reading when the wind moved the fence.
----------
From: [email protected]
[SMTP:[email protected]] on behalf of Flinders, Randall
Sent: Wednesday, November 11, 1998 12:44 PM
To: 'emc-pstc'
Subject: ANSI C63.4
Greetings EMC Professionals!
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JSAnKysrLC4zMzMyLTMzMzMzMzMzMzP/wAARCAABACEDAREAAhEAAxEA/8QA0gAA
AQUBAQEBAQEAAAAAAAAAAwABAgQFBgcICQoLEAABBAEDAgQCBQYGCAcDDWEBAAIR
AwQhEjEFQVFhEyJxgTIGFJGhsUIjJBVSYjM0wXKCQwclkghT0fBjczUW4aLxsoMm
RJNUZEXCo3Q2FxjSVeJl8rOEw9N14/NGJ5SkhbSVxNTk9KW1xdXl9VZmdoaWprbG
1ub2N0dXZ3eHl6e3x9fn9yg4SFhoeIiYqLjI2Oj4CRkpOUlZaXmJmam5ydnp+Qoa
KjpKWmp6P of the concrete.
2) Extending the width of the ground plane to 11.4
meters.
I have four questions to pose to the group:
Question #1 - Does anyone have experience with an
OATS where
the ground plane is covered with concrete? What effect does this
have on
the performance of the site?
Question #2 - ANSI C63.4:1992 does not specify the
minimum
size of the ground plane. Is there a guideline, or can someone tell
me
from
experience, what the minimum size should be?
Question #3 - Does anyone have any feelings on what
the
effect of running the COAX and Power Cables on top of the Ground
Plane can
have on the site performance? Would It be better to raise the
ground plane
off the ground (on a wooded platform) in order to run all of the
cables
under the GRP?
Question #4 - Although there are several trees with
in the
10 meter Ellipse, they are located at the very edges of the Ellipse.
However, there are raised concrete curb planters and waist-high
hedges that
are well within the Ellipse. Can I expect these items to cause
significant
site abnormalities? Also, how far away does a metal object need to
be
before I can consider it safe from causing abnormalities due to
reflections?
Any insight or suggestions on this matter would be
greatly
appreciated. Thanks for your time.
Regards,
Randy Flinders
EMC Engineer
Emulex Network Systems
(714) 513-8012
[email protected]
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