HP 8568B, Performance Tests And Adjustments Manual, Page: 251 / 313

22. Comb Generator Adjustments
Equipment
Cable, SMA (m) to SMA (m) . . . . . . . . . . . . . . . HP 85680-20094
Procedure 1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
Set instrument LINE switch to ON and press
PRESET
).
Connect CAL OUTPUT to SIGNAL INPUT 2.
Key in
FREQUENCY
)
20 MHz,
[
FREQUENCY SPAN
]
100
0 LOG
[
ENTER
2
Adjust front-panel AMPTD CAL for signal peak at top graticule
line (-10
Press
Key in This disables phase lock flags.
Position instrument on right side and remove bottom cover.
Disconnect cables from (PILOT IF OUT) and
IF IN) and connect a short, low-loss coaxial cable with SMA
male connectors ( do not use adapters) between and
Use coaxial cable, HP Part Number 85680-20094. If not
available, remove FILTER and use between and
to adjust comb generator.
Key in
(
START
40 MHz. Wait for CRT annotation at lower
left of CRT display to indicate START 40 MHz.
Key in 1560 MHz. Wait for CRT annotation at lower
right of CRT display to indicate STOP 1560 MHz.
Key in
[
REFERENCE LEVEL
]
-20 0 LOG
(
ENTER
2 DISPLAY LINE -30
Adjust COMB DRIVE for peak amplitude of CRT
trace until comb teeth begin to “wiggle.” Then adjust COMB
DRIVE
slightly counterclockwise until the lowest comb
tooth (near START frequency) just begins to fall. See Figure 3-84
for a typical comb tooth display. See Figure 3-83 for location of
adjustments.
U P P E R L I M I T
D I S P L A Y L I N E
A T - 3 0
L O W E R L I M I T
- 3 6
Figure 3-84. Comb Display
Adjust COMB BIAS for peak amplitude of CRT trace
until comb teeth begin to “wiggle. Then adjust COMB BIAS
slightly counterclockwise until the lowest comb tooth
(near START) frequency) just begins to fall. See Figure 3-84 for
Adjustments