OPERATING MANUAL
C-22
21833-3.4
NORMARC 7013
INSTRUMENT LANDING SYSTEM
Maintenance Procedures ©1999 Navia Aviation AS
before adjusting the transmitter modulation percentage to meet flight inspection tolerances,
advise flight inspection personnel of your situation. If possible, ask them to verify their sys-
tem calibration and check for radio-frequency interference (rfi). Factors that may cause a
difference in modulation percentage readings are:
(a) Excessive carrier component distortion.
(b) FA-9438 calibration correction factor or front panel calibration.
(c) BITE malfunction. With standby equipment, a quick check might be made by transferring
to the standby to check for the same indication.
(d) Transmitter output spectrum and frequency and the 90 and 150 Hz frequencies.
(e) Stray rf pickup by the cable connecting the FA-9438 to the rf wattmeter body coupler may
cause erroneous or inconsistent readings. Double-shielded coaxial cable, such as RG-223/U
will minimize stray rf pickup by the cable.
c. Test Equipment Required.
1. The FA-9438 modulation meter (or equivalent).
d. Conditions.
The facility is operating normally.
e. Procedures.
Refer to Instruction Book TI 6750.141, Installation, Operation, and Maintenance Instructions
for Meter, ILS Modulation, Type FA-9438, section 3, for complete front panel calibration and
operational instructions. The following steps are a digest of those instructions. Steps (1)
through (5) are the front panel calibration steps. The alternate procedure (paragraph g) uses
the oscilloscope to determine the approximate modulation percentage.
1. Turn the FA-9438 ac power switch ON and allow a 10-minute warmup.
2. Place the function selector switch to RF ZERO, and adjust the RF ZERO control for 00.0 on
the PERCENT MODULATION indication.
3. Place the function selector switch to DISPLAY ZERO, and adjust the DISPLAY ZERO con-
trol for 00.0 on the PERCENT MODULATION indicator.
4. Place the function selector switch to CAL 150 Hz, and adjust the CAL 150 Hz control for
42.5 on the PERCENT MODULATION indicator.
5. Place the function selector switch to CAL 90 Hz, and adjust the CAL 90 Hz control for 42.5
on the PERCENT MODULATION INDICATOR.
NOTE:
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.
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