360 Keysight EXG and MXG X-Series Signal Generators User’s Guide
Using Avionics VOR/ILS Softkeys for N5171B/72B and N5181B/82B with Option 302
Using ILS Localizer Softkeys
Using ILS Localizer Softkeys
An ILS [Instrument Landing System] is a navigation system, used by aircraft to
obtain guidance to a runway (performing a “runway approach” while
attempting to land the aircraft) and includes the following three functions
operating in tandem (working together):
— ILS Localizer - ensures that the lateral/horizontal left-right approach of an
aircraft is aligned with the center of a runway
— ILS Glide Slope - ensures that the vertical descent path of an aircraft is
aligned to the proper descent path (~ 3 degrees downwards slope) of a
runway
— ILS Marker Beacons - ensures the proper distance from a runway; the
distances are based on the Outer, Middle, and Inner ILS Marker Beacons
The purpose of the ILS Localizer is to provide signals that indicate whether an
aircraft is left, right, or in-line with the glide path to a runway and enables a
pilot to adjust the aircraft left or right correctly during landing. This
lateral/horizontal correction is performed using two AM signals with an AM
depth of 20%, operating at a carrier frequency range between 108.10 to
111.95 MHz.
For an aircraft on approach, using the ILS Localizer to land on a runway, the
left signal is modulated at a frequency of 90 Hz AM by default and the right
signal is modulated at a frequency of 150 Hz AM by default.
The primary mechanism which makes it possible for a pilot to obtain guidance
to a runway is the aircraft receiver's ability to detect the “Difference in Depth of
Modulation (DDM)” between this 90 Hz AM and 150 Hz AM modulation.
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