TM 11-6625-2781-14&P-2
Section IV
PERFORMANCE TESTS (cont'd)
4-31. Local Oscillator Stability and Residual Frequency Modulation
SPECIFICATION:
Stabilized: less than 20 Hz peak-to-peak. Unstablized: less than 1 kHz peak-to-peak.
DESCRIPTION:
The linear portion of the analyzer IF filter skirt is used to slope detect low-order residual FM. The analyzer is stabilized,
and the detected FM is displayed in the time domain.
1. Make the following control settings:
ANALYZER:
RANGE MHz ................................ ................................ ................................ ................................ .................. 0 -110
FREQUENCY ................................ ................................ ................................ ............................. 0 (LO FEEDTHRU)
BANDWIDTH ................................ ................................ ................................ ................................ ................ 0 1 kHz
SCAN WIDTH ................................ ................................ ................................ ................................ ....PER DIVISION
SCAN WIDTH PER DIVISION ................................ ................................ ................................ ...................... 0 2 kHz
INPUT ATTENUATION................................ ................................ ................................ ................................ ...... 0 dB
SCAN TIME PER DIVISION ................................ ................................ ................................ ...... 50 MILLISECONDS
LOG/LINEAR ................................ ................................ ................................ ................................ ................ LINEAR
LINEAR SENSITIVITY ................................ ................................ ................................ ............................... see below
TUNING STABILIZER................................ ................................ ................................ ................................ .......... ON
VIDEO FILTER ................................ ................................ ................................ ................................ .................. OFF
SCAN MODE ................................ ................................ ................................ ................................ ....................... INT
SCAN TRIGGER ................................ ................................ ................................ ................................ ............ AUTO
2. Turn LINEAR SENSITIVITY and its vernier for a full
eight-division display.
3. Refer to Figure 4-15. Tune FREQUENCY so that
the upward slope of the display intersects the
CENTER FREQUENCY graticule line 1 division
from the top.
4. Note where the slope intersects the middle
horizontal graticule line.
Horizontal
Displacement: divisions
Figure 4-15. Demodulation Sensitivity Measurement.
5. Use the horizontal displacement to calculate demodulation sensitivity:
a. Convert the horizontal displacement (divisions) into hertz.
Example: (0.2 kHz SCAN WIDTH PER DIVISION) x (0.2 div) = 40 Hz
4-21
