TM 32-6625-022-24&P
4-18 SWEEP DRIVE CIRCUIT.
NOTE
Both the 750 MHz marker (extreme left)
a. Set front panel controls to positions described in
and the 1150 MHz marker are now present
on the oscilloscope display. It is essential
b. Connect oscilloscope to sweep
generator as
shown in
to note the positions of these markers now
and during the adjustments perfomed in the
c. Set RANGE switch to UHF position, FREQUENCY
next step of this procedure.
to 1000 Mhz; FINE TUNING control to mid-range.
d. Adjust RF OUTPUT control for an indication of
s. Alternately adjust R145 and R144 CW until 750
0.5 Vrms on RF OUTPUT meter.
MHz marker and 1150 MHz marker are positioned at
e. Adjust oscilloscope controls to obtain a display as
the extreme ends of the horizontal trace as shown in figure
4-15.
f. Set 50 MHz INT MARKER switch to ON.
t. Set SWEEP WIDTH control to NARROW position.
g. Slowly rotate SWEEP WIDTH ADJUST control CCW
u. Rotate SWEEP WIDTH ADJUST control CCW
until only one internal frequency marker remains on
until 1000 MHz marker approximates that shown in figure
ocsilloscope trace. This marker represents a frequency of
4-16.
1000 MHz.
v. Slowly adjust FREQUENCY dial about the 700 MHz
h. Simultaneously continue to slowly rotate SWEEP
point to position 700 MHz marker near the center of
WIDTH ADJUST control CCW and adjust FINE TUNING
oscilloscope trace.
CAL control to maintain marker near center of oscillo-
scope trace.
NOTE
i. While observing 1000 MHz marker, slowly rotate
SWEEP WIDTH ADJUST control CW; note position of this
The 700 MHz marker may not be present on
marker when control is at the maximum CW position.
the oscilloscope trace when the frequency
dial is set exactly on 700 but will appear
NOTE
when the dial is slowly rotated within one
dial division of the 700 MHz point.
When the SWEEP WIDTH ADJUST control
reaches the maximum CW position, the 1000
w. Note extent of deviation between this frequency
MHz marker will usually be to the right of the
dial setting and 700 MHz mark; adjust FREQUENCY
center vertical graticule line.
dial to midpoint of this deviation.
x. Slowly adjust FINE TUNING control to position
j. Rotate SWEEP WIDTH ADJUST control approxi-
y. Set RANGE switch to VHF position.
mately 1/3 CCW.
k. Adjust R139 (MED SWCF) so that 1000 MHz marker
z. Set FREQUENCY dial to 300 MHz.
petition is identical with 1000 MHz marker position when
aa. Slowly adjust C515 (CW OSC FREQ ADJ) to posi-
SWEEP WIDTH ADJUST control is CW.
l. Rotate SWEEP WIDTH ADJUST control CW.
bb. Slowly adjust
FREQUENCY dial about the
0.5 MHz
m. Adjust R144 (WIDE SW LIMIT) CCW until oscillo-
point to position slope of "beat frequency notch" near
scope trace stops shifting (approximately two turns).
cc. Note extent of
deviation between this frequency
n. Determine position of 1000 MHz marker on oscillo-
scope trace by rotating the SWEEP WIDTH ADJUST control
dial setting and 0.5 MHz mark; adjust FREQUENCY
dial to mid-point of this deviation.
dd. Slowly readjust C515 to reposition slope of "beat
then return control to CW position.
o. Using 1000 MHz marker as a reference, determine
frequency notch" near center of oscilloscope trace.
ee. Set SWEEP WIDTH control to WIDE and rotate
position of 750 MHz marker (5th marker to left of 1000
SWEEP WIDTH control CW.
MHz marker).
ff. Adjust FREQUENCY dial to position "beat fre-
p. Adjust R145 (WIDE SWCF) CCW until 750 MHz
marker is at extreme left of horizontal trace.
quency notch" at the extreme left of horizontal trace as
q. Determine position of 1000 MHz marker on oscillo-
gg. Simultaneously adjust FREQUENCY dial to maintain
scope trace (Step n).
"beat frequency notch" at this position and adjust R563
r. Using 1000 MHz marker as a reference, determine
(VHF SW LIMIT) to obtain a 300 MHz bandwidth as
position of 1150 MHz marker (3rd marker to right of
1000 MHz marker).
4-23