Numeric Measurement Modes
R&S
®
EVSG1000
55
User Manual 1178.6227.02 ─ 06
The following scenarios are possible:
●
Predominance of the 90
Hz beam: the aircraft is too far to the left and must turn to
the right
●
Predominance of the 150
Hz beam: the aircraft is too far to the right and must turn
to the left
●
The signal strength from both beams is equal: the aircraft is in the center, on the
right course.
Course and clearance signals
The landing path is divided into the region further away from the runway, referred to as
the course, and the runway itself, referred to as the clearance. Localizers are posi-
tioned in both areas, however they transmit their ILS signals using different frequen-
cies, one that must travel farther, one for close-up. The frequencies differ only in a few
kiloherz. The aircraft always receives both signals, and cannot (and need not) distin-
guish the two. However, for test purposes, it can be useful to measure the signals indi-
vidually.
Morse code identification signal
The localizer not only allows the aircraft to determine its position, it also provides iden-
tification of the ILS transmitter. The localizer periodically transmits a Morse code at
1020
Hz which uniquely identifies the transmitter. The receiver thus knows the ILS is
operating correctly and that it is receiving the correct signal. The glide slope station
does not transmit an identification signal.
4.1.2
Glide Slope Basics
The following description is taken from the Rohde
&
Schwarz Application Note
1MA193: "Aeronautical radio navigation measurement solutions"
The glide slope transmitter is located near the end of the runway (nearest to the start of
the aircraft approach).
ILS Localizer and ILS Glidepath (GP) Modes
