Agilent Technologies 85037A, Operating And Service Manual

Page: 29 / 74

Characterizing the
Detector (P erforming
a P o w er Calibration)
T o obtain the b est accuracy , and to meet the \corrected" dynamic
accuracy sp ecications, eac h detector m ust b e c haracterized on the
8757D input on whic h it will b e used. The c haracterization routine
simultaneously corrects b oth A C and DC measuremen ts. This
routine is also useful as an op erator's c hec k to ensure the detector
is op erating prop erly . Only the 8757D with an Option 002 p o w er
calibrator ha v e this capabilit y .
Detector c haracterization b egins at +20 dBm and decreases in 1 dB
incremen ts do wn to 035 dBm. T o reduce measuremen t time, p o w er
steps are larger than 1 dB at low er p o w er lev els. Correction v alues
will b e generated o v er this range if the detector is op erational. It
will also correct for an y loss in the detector up to ab out 50 dB. F or
example, lets assume a DC detector has a dynamic range of +20 to
050 dBm. A 30 dB attenuator is then placed on the detector and a
c haracterization is p erformed. Up on completion, the detector will b e
c haracterized from +20 to 020 dBm. Applying a 0 dBm signal to
the detector/pad com bination will result in a 0 dBm reading; not a
030 dBm reading whic h is what the detector itself is actually seeing.
A loss of more than ab out 50 dB may result in an error message
b eing display ed on the analyzer. This could o ccur if the detector is
defectiv e or if y ou simply forgot to connect the detector under test to
the P o w er Cal Output of the 8757D.
Up on completion of this routine, the dynamic range of the detector
will b e display ed; v erify that it is correct for the curren t detection
mo de, taking in to accoun t an y attenuation due to added pads or
other devices, or due to inheren t loss, suc h as in a directional bridge
whic h t ypically has 12.5 dB of loss.
T o c haracterize the detector (p erform a p o w er 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
b een on and the detector connected for at least 30 min utes.
1. Press 4 CAL 5.
2.
Select
NNNNNNNNNNNNNN
MORE .
3.
Select
NNNNNNNNNNNNNNNNNNNNNNNNNNNNN
POWER CAL .
4.
Select
NNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNN
DET A,B,C or R .
5.
Select
NNNNNNNNNNNNNNNNNNNNNNNNNNNNN
START CAL .
A complete c haracterization for one detector takes ab out 60 seconds.
Once c haracterized, do not unplug the detector from the analyzer or
y ou will ha v e to p erform another c haracterization. This is b ecause
the 8757 automatically recalibrates itself when it senses a detector
has b een remov ed or connected to the detector inputs. Ho w ev er,
the analyzer c an b e turned o and on again without losing this
information. P erform the c haracterization at least once p er da y and
more often if the temp erature v aries b y more than 65 C.
Operation 3-7