OPERATING MANUAL
C-14
21833-3.4
NORMARC 7013
INSTRUMENT LANDING SYSTEM
Maintenance Procedures ©1999 Navia Aviation AS
(c) Confirm that the times measured are within the operating tolerances of chapter 3.
(d) Restore the facility to service operations.
5-21 Reserved
5-22 SIDEBAND NULL.
a. Object.
This procedure provides a method to determine the position of the sideband null relative to
course centerline.
b. Discussion.
The location of the sideband null and its coincidence with the course centerline affords opti-
mum structure of the localizer course. A null in the sideband radiation pattern occurs when
sideband energy from one-half of the localizer array is received concurrently with an equal
amount of opposite phased energy from the other half. If an amplitude inequality occurs
between the two halves, the resulting energy difference converts the former null into a side-
band intensity minimum. Altering the 180° sideband phase relationship between the two
halves shifts the null (or minimum) toward the side with the greater delay (lagging phase).
Reflections also modify the null depth and position. Rotating the array moves the null position
degree for degree.
c. Test Equipment Required.
1. A portable ILS receiver (PIR).
2. An audio meter.
3. A directional antenna, such as a Yagi designed for localizer frequencies, is highly recom-
mended.
d. Conditions.
A facility shutdown is required for this check.
e. Detailed Procedure.
1. Feed carrier, modulated by a continuous 1020 Hz tone, into the sideband input to the
antenna array.
2. Position the PIR on the course centerline. The distance to the array should be as far as
possible while still maintaining a sharp null indication. A directional antenna should be
used with the PIR if available.
3. Locate the rf null as indicated by minimum audio or rf level from the PIR.
4. Measure the null displacement from the course (centerline).
5. Using English units: Divide the measured displacement in inches by the distance to the
array in 1000's of feet. For example: the sideband null is measured 1500 feet from the
array and found at 17 inches from course centerline.
OR;
Using metric units: Divide the measured displacement in centimeters by the distance to the
array in 300's of meters. For example: the sideband null is measured 450 meters from the
array and found at 45 centimeters from course centerline.
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