Shift Peak; Shift Pwr Sweep; Shift Slope - HP 8340B Manual

3.
Use the step keys to set the 90 dB attenuator,
and the data
entry keyboard, or the front panel
knob, set the
MOD
(linear modulator):
a.
Set MOD
entry at
0
dBm.
b.
Increment
the ATN
until the
POWER dBm display
shows
a
level
of
5
to
15
dB higher than the
desired output power.
c.
Reduce the power to the desired
level
by changing the MOD value.
Because the
actual
power
changes very
little as the pulse width
is narrowed, even though the POWER
dBm reading drops, at very narrow pulse widths ignore this reading.
The
ATN and MOD
values
in the
ENTRY DISPLAY
also have a
limitation:
Although the ATN displayed value
is
always accurate, MOD becomes
saturated in
the top 10 dB
(approximately) of
its
range. At
this point
no change occurs
in the true power. Because of
this,
rely
on the
POWER dBm display for the
true power
level
instead of the
MOD
value.
SHIFT METER
can
also be used as
a
diagnostic function of the ALC
circuits.
SHIFT PEAK (HP-IB: SHRP)
This
is
a
more extensive version of peaking. PEAK, which requires
a
fraction of
a second
to imple¬
ment, aligns the output filter with
a single
CW frequency; SHIFT PEAK
aligns
all of the
YTM
tracking
calibration constants and requires
5
to
10
seconds
to
implement.
Use
SHIFT PEAK to
enhance the power output and spectral
purity of
swept
modes, and to improve
tracking
performance
(especially in harsh environments having wide temperature variations).
1.
Press [SHIFT] [PEAK].
AUTO TRACKING appears
in
the ENTRY DISPLAY for 5
to
10
seconds.
When the
message
disappears, the instrument has completed the power peaking function and updated working
calibration constants.
SHIFT PWR SWEEP (HP-IB: SHPS)
This function decouples the
90 dB
step attenuator (ATN) from the automatic
leveling control (ALC).
To
recouple
the
attenuator and ALC loop, press [POWER LEVEL].
SHIFT SLOPE (HP-IB: SHSL)
This function allows front panel control
of the 90 dB
step attenuator (ATN).
1.
Press [SHIFT] [SLOPE].
ATN: xdB appears
in
the
ENTRY DISPLAY (x
is the last
entered value).
2.
Use the
[STEP] keys
or the data entry keyboard with any termination key to
change the ATN value
within
the range
0 dB to —90 dB
in
10 dB
steps.
Keyboard entries are rounded to the nearest
10
dB.
The
clicking sound heard after each
attenuator change
is
the attenuator pad mechanically switching into
the RP output path.
A-30
Assembly-Level Service
Front Panel Diagnostics
HP 8340B/41B