HP 8340B Manual page 183

5-14. UNLEVELED RF OUTPUT ADJUSTMENTS (Cont'd)
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]
[PWRSWP] and set the ALC level, using the OUT'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] a nd 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 adlustments.
the trace goes off the oscilloscope display in the following adjustments, adjust the vertical
11. If
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
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 SRD 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 (SRO
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
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
NOTE
0.5 dB.
14. If TP12
Adjustments 5-77