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Characterizing the
Detector (Performing
a Power Calibration)
o obtain the best accuracy, and to meet the \corrected" dynamic
accuracy speci cations, each detector must be characterized on the
8757D input on which it will be used. he characterization routine
simultaneously corrects both AC
routine is also useful as an operator's check to ensure the detector
is operating properly. Only the 8757D with an Option 002 power
calibrator have this capability.
Detector characterization begins at +20 dBm and decreases in 1 dB
increments down to
steps are larger than 1 dB at lower power levels. Correction values
will be generated over this range if the detector is operational. It
will also correct for any loss in the detector up to about 50 dB. For
example, lets assume a DC detector has a dynamic range of +20 to
0
50 dBm. A 30 dB attenuator is then placed on the detector and a
characterization is performed. Upon completion, the detector will be
characterized from +20 to
the detector/pad combination will result in a 0 dBm reading; not a
0
30 dBm reading which is what the detector itself is actually seeing.
A loss of more than about 50 dB may result in an error message
being displayed on the analyzer. his could occur if the detector is
defective or if you simply forgot to connect the detector under test to
the Power Cal Output of the 8757D.
Upon completion of this routine, the dynamic range of the detector
will be displayed; verify that it is correct for the current detection
mode, taking into account any attenuation due to added pads or
other devices, or due to inherent loss, such as in a directional bridge
which typically has 12.5 dB of loss.
o characterize the detector (perform a power cal), connect the
detector to the desired input of the 8757D. Connect the RF input of
the detector to the calibrator output. Make sure the analyzer has
been on and the detector connected for at least 30 minutes.
1. Press
.
CAL 5
2. Select
.
MORE
3. Select
POWER CAL
4. Select
DET A,B,C or R
5. Select
START CAL
A complete characterization for one detector takes about 60 seconds.
Once characterized, do
you will have to perform another characterization. his is because
the 8757 automatically recalibrates itself when it senses a detector
has been removed or connected to the detector inputs. However,
the analyzer
be turned o and on again without losing this
can
information. Perform the characterization at least once per day and
more often if the temperature varies by more than
DC measurements. his
and
0
35 dBm. o reduce measurement time, power
0
20 dBm. Applying a 0 dBm signal to
.
.
.
unplug the detector from the analyzer or
not
6
5
C.
Operation 3-7
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