TM 11-6625-2781-14&P-2
Section IV
PERFORMANCE TESTS (cont'd)
4-31. Local Oscillator Stability and Residual Frequency Modulation (cont.)
b. Calculate demodulation sensitivity by dividing the vertical displacement in divisions into the horizontal
displacement in Hz:
40 Hz
Example:
= 13.3 Hz/DIV
3 divisions
NOTE
13.3 Hz/div is a typical value, and may be used for stability measurements.
6. Turn SCAN WIDTH to ZERO scan. Tune FINE TUNE for a response level within the calibrated three-division range
(1 division from the top to the center horizontal graticule line).
7. Measure the peak-to-peak deviation, and multiply it by the demodulatio n sensitivity obtained in step 5 above.
Example: 0.5 div p-p signal deviation x 13.3 Hz/div = 6.65 Hz Residual FM
20 Hz (peak-to-peak)
8. To measure unstabilized residual FM, repeat the test with the following control settings:
TUNING STABILIZER................................ ................................ ................................ ................................ .......... ON
BANDWIDTH ................................ ................................ ................................ ................................ ................... 1 kHz
SCAN WIDTH ................................ ................................ ................................ ................................ ....PER DIVISION
SCAN WIDTH PER DIVISION ................................ ................................ ................................ ......................... 1 kHz
SCAN TIME PER DIVISION ................................ ................................ ................................ ...... 50 MILLISECONDS
9. Calculate demodulation sensitivity as in steps 2 through 5. A typical value for demodulation sensitivity with the
control settings given is 135 Hz/div.
10. Switch to ZERO scan, TUNING STABILIZER to OFF, and turn FINE TUNE so that the display occurs in the
calibrated three-division range (1 division from the top, to the center horizontal graticule line).
11. Measure the vertical displacement and multiply it by the demodulation sensitivity obtained in step 9 above.
1 kHz (peak-to-peak)
4-22
