TM 11-6625-2575-14
analyzer operator's manual, and proceed as fol-
k. Subtract the frequency obtained in j above
lows:
from the frequency obtained in i above.
(1) Display the rf amplitude in the fre-
quency domain.
maximum.
(2) Calibrate the display amplitude in dB.
8-15. Spurious and Harmonic Distortion
(3) Obtain a display of the fundamental
frequency of the unit under test.
a. Connect the RF OUT connector of the unit
under test to the input of the spectrum analyzer.
e. While gradually adjusting the CENTER
FREQUENCY of the unit under test, tune the
b. Set the front panel controls of the unit under
main dial of the spectrum analyzer, and observe
test as follows:
spurious and harmonic responses of the unit un-
(1) SWEEP WIDTH switch - - - - - - - CW.
der test. Any spurious signal or harmonic compon-
(2) MARKERS - - - - - - - - - - - - - - - -All OFF.
(3) RF VERNIER - - - - - - - - - - - - - - - - -0.5 volt rms. ent shall be at least 25 dB below the fundamental
(4) BAND switch - - - - - - - - - - - - - - - - - LOW.
frequency (CENTER FREQUENCY) of the unit
(5) ALC - - - - - - - - - - - - - - - - - - - - INT.
under test.
(6) ATTENUATOR - - - - - - - - - - - - - 0dB.
f. Repeat e above with the BAND switch set
c. Adjust the CENTER FREQUENCY from
to HIGH and at the same time, adjust the CEN-
20 to 300 MHz.
TER FREQUENCY of the unit under test from
300 to 1200 MHz.
d. Follow the instructions in the spectrum
Section V. ALIGNMENT AND ADJUSTMENT
PROCEDURES
8-17. General Alignment and Adjustment
8-19. Rate Generator, Frequency Dial, and
Information
Sweep Width Alignment
a. When a repaired AN/USM-203A has been
tested as required in Section V, alignment and
sweep width, follow the procedures in para-
adjustment procedures may be required. The pur-
graphs 7-13 through 7-15, respectively.
pose of Section VI is to enable a repaired unit
to meet the technical characteristics in para-
8-20. Rf
Output Voltage Adjustment
graph 1-11 by resetting internal controls.
Adjust the rf output voltage by performing the
b. Be careful when making adjustments to
correct a given out-of-tolerance condition. An ad-
justment which corrects one condition may de-
8-21. Marker Amplitude Adjustment
grade another. When an adjustment affects more
Adjust the marker amplitude by performing the
than one operating characteristic, another ad-
justment must be used to bring the system into
balance. A series of alternate adjustments may
NOTE
be required to achieve the desired results.
Marker frequency accuracy may be
checked by zero-beating an external sig-
c. Because some of the AN/USM-203A adjust-
ments do interact, repeat the test procedures in
frequency counter with displayed 1.0-,
Section V in sequence after final adjustments
10.0-, and 50.0-MHZ internal markers
are made.
in the AN/USM-203A.
8-18. Power Supply Adjustment
8-22. Blanking Mode Selection
NOTE
NOTE
Adjustment of the power supply volt-
BLANKING switch S102 must be set
ages may cause major misalignment of
to VIDEO (normal position) when set-
both the HIGH and LOW BAND CEN-
ting the RF OUTPUT. In the RF posi-