OPERATING MANUAL
C-8
21833-3.4
NORMARC 7013
INSTRUMENT LANDING SYSTEM
Maintenance Procedures ©1999 Navia Aviation AS
It may be necessary to repeat steps (2) through (5) occasionally as the FA-9438 warms up.
6. Use a double-shielded coaxial cable and connect the modulation meter to the COU CSB
test connector on the front of the facility. Insert a 20 dB attenuator at the input of the modu-
lation meter.
7. Place the function selector switch to LOCALIZER or GLIDE SLOPE, as appropriate, and
read the 90 Hz and 150 Hz modulation percentages on the PERCENT MODULATION indi-
cator.
8. Record the percentages on FAA Form 6750-32, and determine if they are in tolerance.
9. At two-frequency facilities, complete the steps above for the clearance transmitter on a dif-
ferent FAA Form 6750-32. (Test cable connected to CLR CSB test connector.)
10.Restore the equipment to normal.
5-15 IDENTIFICATION TONE MODULATION PERCENTAGE.
a. Object.
This procedure provides a method to determine the modulation percentage of the localizer
identification tone.
b. Discussion.
This method rely on the fact that the amplitude of the 1020 Hz audio signal detected from the
carrier feedline is proportional to the percent of carrier modulation. The detected audio con-
tains 90 and 150 Hz components with amplitudes proportional to the 90 and 150 Hz modula-
tion percentages. By comparing the relative amplitudes of the 1020 Hz with the 90 and 150
Hz components, the relative identification modulation percentage can be determined.
c. Test Equipment Required.
1. A digital voltmeter (dvm).
d. Digital Voltmeter Procedure.
1. Switch the ident tone and one of the navigation tones (90 or 150 Hz) off.
2. If the modulation percentage of the navigation tones is not known, measure the modulation
percentage of the remaining navigation tone, using the FA-9438 modulation meter or
equivalent.
3. Connect a dvm, set to read ac millivolts, to the transmitter CSB test connector. Record the
dvm reading.
4. Switch the navigation tone off and the ident tone to continuous. Record the dvm reading.
5. Calculate the ident tone modulation percentage with the following formula:
Ident mod% =
6. Switch both navigation tones on and the ident tone to normal.
Nav Tone Mod x Ident Tone DVM ading
Nav Tone DVM ading
%Re
Re
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