TM 11-5840-360-14-1-1
center of the CRT, then turn R50 CCW until diameter of
NOTE:
the dark circle is reduced to between 1/8 and 1/16 inch.
If the difference between step 10 and
11 current measurements exceeds 5
NOTE:
microamperes, a new pair of
matched crystals (CR5 and CR6)
Under adjustment of the STC Delay
should be installed in the mixer
control R50 will result in degraded
assembly.
minimum range performance; over
adjustment may cause burning of the
CRT face.
12. At master Indicator, adjust TUNE, GAIN and
6. At master Indicator set RANGE SELECT switch to
CONTRAST controls to optimize CRT target display.
1.5 MILES. If attenuation of returns from significant
short range targets is noted, re-adjust STC Law control
5.10.3.8 Anti-Clutter Sea (STC) Adjustment. - The STC
R57 on Receiver Transmitter RT-1240 to optimize target
circuit has been factory adjusted.
However, re-
display.
adjustment may be necessary for a particular installation
or following repairs. If, after careful evaluation of
NOTE:
performance, if it is determined that readjustment is
This re-adjustment may alter the 3-
necessary, the following procedure shall be used.
mile noise cutoff established in step
3 and degrade STC performance;
NOTE:
perform the re-adjustment with care.
The range zero alignment procedure
given in paragraph 5.12.3.3 must
5.11 ANTENNA PEDESTALS AB-1247 AND AB-1247A
have been accomplished prior to
performance of the procedure.
subparagraphs
provide
corrective
maintenance
1. At master Indicator:
information for Antenna Pedestals AB-1247 (V1, V2, V3
a. Set POWER switch to TX ON.
X-band) and AB-1247A (V4 X-band, with synchro
b. Set RANGE SELECT switch to 6 MILES.
transmitter). The information includes troubleshooting
instructions (5.11.1), removal and replacement
c. Set GAIN control fully CCW.
d. Set ANTI-CLUTTER SEA control fully
The locations of assemblies and major components
CCW.
within the antenna pedestals are shown in Figure 5-4.
e. Allow 3.5-minute time delay to elapse.
Schematic diagrams, parts list tables and assembly
2. Adjust master Indicator BRILLIANCE control so
drawings applicable to the AB-1247 and AB-1247A
that CRT trace is barely visible, then adjust GAIN
pedestals are contained in Section 6.3 of Chapter 6.
control to display a background noise speckle.
Primary access to the assemblies and components
3. Set master Indicator ANTI-CLUTTER SEA
within the AB-1247 and AB-1247A antenna pedestals is
control fully CW; verify background noise speckle is
provided by disconnecting the waveguide fitting from the
diminished to a range of at least 3 miles. If incorrect,
rotary joint, disconnecting the pedestal housing from the
adjust R57 (STC Law control) on Receiver Transmitter
fixed base plate, and raising the housing until it locks
RT-1240 A 1100 PCB.
into its service position.
4. At master Indicator:
Detailed instructions for raising the pedestal in this
manner are given in the appropriate procedures.
a. Set RANGE SELECT switch to .5 MILES.
b. Adjust ANTI-CLUTTER SEA control CCW
WARNING
until well defined short range targets are
WHEN WORKING AT TIIE ANTENNA
displayed.
PEDESTAL, ALWAYS SET THE
5. Turn STC Delay control R50 on Receiver
ON/OFF SAFETY SWITCH (LOCATED
Transmitter RT-1240 CW to display a dark circle at the
ON TIIE FRONT EX| TERIOR OF TIIE
PEDESTAL) TO OFF.
5-24
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