Local Oscillator Stability and Residual Frequency Modulation

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