HP 8340B Manual page 276

5-14.
UNLEVELED RF OUTPUT ADJUSTMENTS (Cont'd)
NOTE
After
you have
peaked the
power
in
the band you are adjusting, you can
determine the approximate power per division on the oscilloscope (for
a
specific vertical sensitivity) by perform the following. Press [MANUAL]
and note the power
level
in
the POWER dBm display. Press [SHIFT]
[PWR SWP] and set the ALC
level, using
the DUT's front panel rotary
knob, to the noted power level. Turn
the rotary knob counter-clockwise
to
place the dot
on
the oscilloscope to
a
convenient
horizontal graticule
and
note
the power level in
the POWER dBm display. Turn the rotary
knob counter-clockwise
to
place the dot
on the next horizontal
graticule
and note the power
level.
The difference between the two readings is the
dB/Div sensitivity
on
the oscilloscope. Repeat
this
procedure for several
horizontal divisions on
the scope since the dB/Div will
change
slightly
as
the power level is
changed (due to the output characteristics of the
detector). If you wish to verify
the sensitivity at other frequencies, press
[MANUAL] and
turn the rotary knob for
the desired frequency and then
repeat
this
procedure.
After completing
this
procedure, press [RECALL]
[1]
to return to the instrument state required for the adjustments.
11. If the trace goes off the oscilloscope display
in the following adjustments, adjust the vertical
position
and/or
sensitivity
controls to view the entire trace
on
the display.
Adjust A24R3 (X2A) to optimize
the
power
in
the first half of the display.
Adjust
A24R4 (X2B)
to optimize the
power
in the
second
half of the display.
If
the output
power
begins to decrease while adjusting one of
these
potentiometers (pots)
clock¬
wise (i.e., power reversal, squegging), adjust the pot counter-clockwise
until the
power
is peaked
again and then continue turning the pot counter-clockwise until the power
is
reduced
s=
0.5 dB.
It
may
be desirable to optimize the power in one half of the band (maximum
power
with no
squegging), even though squegging
is
induced
in the other
half. One
would do this
if the side being
adjusted is
significantly lower
in
power
than the other half. Once the power is
optimized, adjust the
bias
in
the other
half (using
the
pot for that half) to eliminate squegging. Iterate
between the two
adjustments to optimize the power and
to ensure that there
is
no squegging in either half.
If
squegging
occurs
in the center of the swept display (one
division left or right of center), adjust
X2A counter-clockwise to eliminate the squegging. Adjusting X2A
to eliminate squegging
in the
center of the band will hopefully force the
3RD
BIAS test point (A24TP12)
into
a
slight
upward
slope.
12.
Adjust
A28R6 (OFST)
and
A28R82 (GAIN)
for optimum power across the entire display.
13.
Repeat step
11.
After this, disconnect the detector and connect the scope probe
to
A24TP12 (SRD
BIAS) as shown
in
Figure
5-40.
Adjust the
scope's
vertical sensitivity to view the
waveform on
TP12.
If TP12
exhibits
a
slight upward slope,
as shown
in
Figure 5-42, proceed to step
14.
If TP12
exhibits
a
flat or
downward slope,
adjust X2A until
a
upward slope is
displayed on TP12 (do not
adjust X2A more than 1/8 of
a
turn).
If adjusting X2A does
not provide an
upward slope on TP12,
adjust X2B
until
a upward slope
is
displayed on TP12 (do not adjust X2B more than 1/8 of
a turn).
If
neither of these adjustments provide an upward slope on TP12, repeat steps
9
through
13.
HP 8340B/41B
Adjustments
5-77