Service manual

STP 11-25R13-SM-TG
3 - 47
Performance Steps
( b) From 100 Hz to 7.5 kHz, THD is 2.5 percent.
( c) From 7.5 kHz to 15 kHz, THD is 3 percent.
(5) With a 1 kHz reference level, check that the demodulated frequency response is within +/-
2 dB from 100 Hz to 5 kHz at 25, 50, 75, and 100 percent modulation.
(6) Check that the system noise output level from 50 Hz to 15 kHz is at least 60 dB below 100
percent modulation level, with a 400 Hz modulating reference.
(7) Check spurious emissions from the carrier using the unmodulated carrier as a reference.
( a) Attenuate emissions between 120 kHz and 240 kHz at least 25 dB.
( b) Attenuate emissions between 240 kHz and 600 kHz at least 35 dB.
( c) Attenuate emissions more than 600 kHz at least 80 dB.
(8) Operate the pilot subcarrier at 19 kHz +/- 2 Hz.
(9) Operate the stereo subcarrier at 38 kHz +/- 4 Hz.
(10) Check that the separation between any two channels of a stereo transmission system
does not exceed 29.7 dB for all modulation frequencies between 50 Hz and 15 kHz.
(11) Check that the nonlinear crosstalk between any two channels of a stereo transmission
system does not exceed 40 dB for all modulation frequencies between 50 Hz and 15 kHz.
(12) Check that the 19 kHz pilot subcarrier modulates the main carrier between the limits of 8
to 10 percent.
(13) Check that the sum of the sidebands resulting from the amplitude modulation of the
stereophonic subcarrier does not cause a peak deviation of the main carrier more than 45
percent of total modulation (excluding SCA subcarrier).
3. Localize the trouble to a specific circuit by analyzing overall block diagrams and by performing
functional tests on suspected circuits.
4. Isolate the fault to a component.
a. Perform resistance and continuity tests with a multimeter.
b. Perform power distribution voltage tests.
5. Replace, repair, or adjust faulty component.
6. Operations check the transmitter by verifying the applicable specifications according to performance
step 2c or 2d; readjust or align as necessary.
7. Complete DA Form 2407 using the appropriate codes listed in DA Pam 738-750.
8. Turn the DA Form 2407 into the supervisor to inspect work.
Performance Measures Results
1. Review DA Form 2407. P F
2. Sectionalize the trouble to a defective stage. P F
a. Visually inspect for discrepancies. P F
b. Turn ON power and allow for a 5-minute warm-up time. P F
c. Check specifications for an AM or FM transmitter. P F
3. Localize the trouble to a specific circuit. P F
4. Isolate the fault to a component. P F
a. Perform resistance and continuity tests. P F
b. Perform power distribution voltage tests. P F
5. Replace, repair, or adjust faulty component. P F
6. Operations check by verifying applicable specifications; readjust or align as necessary. P F
7. Complete DA Form 2407. P F