Cokeva
11940C
Operation Note
3
3
‐
1.
OPERATION
3
‐
2.
Theory
of
Operation
3
‐
3.
The
Cokeva
11940C
is
a
balanced
magnetic
field
sensor
that
provides
an
output
voltage
proportional
to
the
strength
of
the
magnetic
field
at
its
tip.
Radiated
magnetic
fields
couple
directly
to
the
Cokeva
11940C
and
produce
an
output
signal;
radiated
electric
fields
also
couple
to
the
Cokeva
11940C
but
do
not
produce
an
output
voltage
due
to
the
construction
of
the
probe.
The
Cokeva
11940C
uses
a
dual
‐
loop
sensor
and
a
balun
to
reject
electrically
coupled
signals.
See
Figure
2.
The
probe
preserves
frequency
information
and
is
ideally
suited
for
use
with
a
spectrum
analyzer.
The
Cokeva
11940C
circuitry
is
passive
and
therefore
only
contributes
thermal
noise
to
any
measurement
system.
Inspect
the
probe
tip
for
damage
before
using.
Figure
2.
Magnetic
Field
Orientation
for
Maximum
Coupling
3
‐
4.
Antenna
Factors
3
‐
5.
The
Cokeva
11940C
is
supplied
with
a
calibration
table
mounted
on
its
side.
The
table
provides
antenna
factors
at
five
calibration
points:
30
MHz,
100
MHz,
500
MHz,
850
MHz,
and
1000
MHz.
The
antenna
‐
factor
units
used
in
this
table,
dB(
μ
A/m/
μ
V),
are
accurate
to
±2
dB
in
a
377
ohm
field
impedance.
Add
the
antenna
‐
factor
units
to
the
measured
voltage
in
dB
μ
V
indicated
on
the
spectrum
analyzer
to
give
magnetic
‐
field
strength
in
dB(
μ
A/m).
Refer
to
the
following
equation:
