OPERATING MANUAL
C-12
21833-3.4
NORMARC 7013
INSTRUMENT LANDING SYSTEM
Maintenance Procedures ©1999 Navia Aviation AS
2. Measure the rf frequency of the transmitter(s) by connecting the counter to the COU CSB
test connector on the front of the facility. The transmitter must be operating for at least 15
minutes before measuring rf frequency. The audio modulation may have to be removed to
obtain a constant counter readout.
3. Record the results obtained in steps (1) and (2) on the appropriate form. If any frequency
or the frequency separation at two-frequency facilities is out of tolerance, corrective action
shall be taken.
4. The transmitter rf frequency should be adjusted as close to the authorized frequency as
possible, and shall be adjusted to within the initial tolerances specified in chapter 3. Fol-
lowing rf frequency adjustment, the final measurement should be performed at least 5 min-
utes after the last adjustment is made. This is to allow the oscillator sufficient time to settle
to its final operating frequency. Adjustment point is C1 in OS1221A module accessible thru
a single hole in the box enclosure.
5-19 AUDIO PHASING.
a. Object.
This procedure provides a method to determine that the audio phase relationship between the
150 Hz modulation tones of the path and clearance transmitters (for glide slope) or the 90 Hz
and 150 Hz modulation tones of the course and clearance transmitters (for localizer) are in
phase.
b. Discussion.
The audio phase relationship between the course and clearance signals must be in phase to
ensure that these signals always add to and not subtract from each other. This is true for both
localizers and glide slopes. When an aircraft is in transition between a predominance of sig-
nal from the course, and clearance transmitter, these signals may be approximately equal.
When this occurs, a false course or path could be produced if the audio phasing is out of
phase. Navigation audio signals may be sampled via an rf wattmeter only with a suitable ele-
ment installed, or an equipment test point(s) depending on the facility type.
c. Test Equipment Required.
1. An oscilloscope with an accurately calibrated time base.
2. A BNC tee-adaptor, male input, female outputs.
d. Conditions.
The facility must be removed from service.
e. Detailed Procedure.
1. Connect the oscilloscope Y INPUT to observe the course (or path) transmitter 150 Hz out-
put. The connection point is the course transmitter CSB test connector. Switch off the iden-
tification modulation and the 90 Hz tone.
2. Connect the oscilloscope TRIGGERING INPUT to the course (or path) transmitter 150 Hz
output, same output as in (1) using a BNC tee-adaptor.
3. Adjust the triggering so that the waveform crosses the zero axis at the center of the oscillo-
scope display.
4. Connect the oscilloscope Y INPUT to observe the clearance transmitter 150 Hz output. The
connection point is the clearance transmitter CSB test connector. DO NOT ADJUST ANY
CONTROLS.
5. Confirm that the positive and negative peaks are in the same position on the oscilloscope
as the course transmitter.
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