Comb
Generators
model
CGO
‐
520
Page
10
of
11
(949)
459
‐
9600
www.com
‐
power.com
Rev.
0216
Compare
these
levels
with
all
subsequent
measurements
to
make
sure
that
the
pattern
does
not
have
abrupt
change
from
the
established
daily
log
at
any
frequency.
The
more
higher
the
number
of
frequency
points
the
higher
the
accuracy
of
the
reference
measurements.
This
log
is
used
to
detect
any
test
equipment
or
test
site
related
problem
as
described
below.
Problems
Related
to
Test
Equipment
Variation
on
the
log
of
the
Comb
Generator
output
data
is
dependent
on
the
test
equipment
as
well
as
site.
The
Comb
Generator
replaces
the
EUT.
The
Comb
Generator
not
only
generates
the
output
simultaneously
at
all
the
harmonics,
but
it
minimizes
any
variation
of
its
output.
This
is
achieved
by
utilizing
a
stabilized
signal
circuit
as
well
as
geometry
of
the
radiator.
The
circuit
stability
is
maximized
by
design,
whereas
the
geometry
of
the
radiated
source
is
optimized
by
eliminating
all
cables
during
the
Radiated
Emission
Mode.
The
typical
variation
of
Comb
Generator
output
at
any
frequency
is
less
than
±
1
dB.
With
the
variations
due
to
the
EUT
practically
eliminated,
only
variations
remaining
are
due
to
other
factors,
mainly
the
test
instrumentation
and
the
site.
The
variation
due
to
test
instrumentation
is
limited
to
the
sum
total
of
the
tolerance
on
all
test
equipment
used
(spectrum
analyzer,
antenna,
preamplifier,
cables).
A
few
days
of
data
will
establish
the
range
of
variation
to
be
expected
at
a
site.
This
is
generally
less
than
±
3
dB.
Any
variation
in
the
readings
above
normal
variation
indicates
a
potential
problem.
After
the
daily
log
is
established
for
a
few
days,
any
problem
is
easily
detected
as
a
larger
variation.
This
procedure
allows
immediate
detection
of
a
major
problem
with
the
test
equipment.
Problems
Related
to
site
The
above
procedure
cannot
distinguish
the
problems
related
to
the
test
site.
The
Comb
Generator
can
be
used
in
two
ways
to
detect
any
problem
with
a
test
site.
One
method
is
to
start
the
daily
log
immediately
after
the
test
site
is
calibrated.
This
way,
one
is
certain
about
the
validity
of
the
data
taken
on
the
test
site.
The
second
method
is
to
calibrate
the
Comb
Generator
radiated
output
as
absolute
emission
level.
Such
calibration
is
provided
as
an
option
with
the
Comb
Generators.
In
addition,
when
difficulty
arises
with
any
EUT
data
taken
at
two
different
sites,
the
Comb
Generator
can
be
used
to
determine
if
both
sites
give
reliable
results,
just
by
comparing
the
data
at
the
two
sites
with
the
Comb
Generator.
In
this
case,
if
the
two
sites
do
not
produce
comparable
results,
a
Comb
Generator
with
calibrated
data
is
certainly
required
to
determine
the
faulty
site.
Problems
Related
to
Test
Personnel
The
Comb
Generator
cannot
directly
help
to
eliminate
the
test
personnel
related
problems.
However,
by
increasing
the
confidence
level
and
establishing
definite
procedures
for
eliminating
site
and
equipment
related
problems
it
helps
tremendously
to
reduce
the
problems
related
to
EMI
measurements.
