Comb
Generators
model
CGO
‐
520
Page
9
of
11
(949)
459
‐
9600
www.com
‐
power.com
Rev.
0216
Application
Radiated
Emissions
EMI
test
sites
such
as
Open
Area
Test
Site
(OATS)
or
Anechoic
chambers
are
constructed
with
specific
requirements
and
are
calibrated
in
a
precise
manner
to
optimize
the
reliability
of
the
emissions
measurements.
The
time
and
expense
incurred
is
considered
essential
to
increase
the
repeatability
of
the
data.
The
data
taken
on
the
above
sites
are
generally
reliable.
However,
in
some
instances,
discrepancies
do
occur,
and
the
reliability
of
data
is
questionable.
Such
discrepancies
could
be
discovered
when
either
(a)
data
from
two
sites
for
the
same
equipment
do
not
match,
or
(b)
the
data
from
two
different
occasions
for
the
same
equipment
at
the
same
OATS
are
not
consistent.
It
is
important
to
find
the
cause
for
such
inconsistency.
This
is
generally
a
very
time
consuming
and
difficult
process
because
the
reason
could
be
one
of
four
complex
factors.
(1)
Equipment
under
test
(EUT),
(2)
The
Test
Site
(3)
Instrumentation
(4)
Test
personnel.
Each
of
these
factors
may
have
many
possible
causes.
The
EUT,
for
example,
may
have
changed
due
to
component
variation,
temperature,
operating
mode,
wear
and
tear,
design
etc.
The
test
site
may
be
a
cause
due
to
a
reflective
object
near
the
site,
variation
of
ground
saturation
or
ambient
signal
presence.
It
also
could
be
due
to
malfunctioning
test
instrumentation.
By
establishing
simple
measurement
procedure
similar
to
the
one
described
below
the
test
lab
can
reduce
occurrence
of
these
problems.
There
by
increasing
the
reliability
of
measurements
taken
on
the
site.
The
procedure
described
is
just
a
guide
and
can
varied
according
to
your
needs.
Measurement
Procedure
As
mentioned
before,
taking
measurement
more
frequently
is
important.
Create
a
log
with
frequency
and
levels
that
you
would
like
to
record.
This
can
be
daily,
weekly
or
monthly
log.
We
recommend
taking
Comb
Generator
measurement
before
to
starting
a
radiated
emissions
test.
Set
up
the
Comb
Generator
with
the
appropriate
antenna
(see
frequency
range
on
page
3).
Put
the
Comb
Generator
where
the
equipment
under
test
(EUT)
is
normally
placed
during
the
test.
Make
a
measurement
like
you
would
on
a
EUT.
We
recommend
using
discrete
frequency
points
rather
than
a
wide
frequency
sweep.
Such
as
30
MHz,
40
MHz,
100
Hz,
900
MHz,
etc.
Record
the
level
for
each
frequency.
