Keysight EXG and MXG X-Series Signal Generators User’s Guide
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Avionics VOR/ILS (Option 302)
Using ILS Glide Slope Softkeys
Using ILS Glide Slope 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 Glide Slope is to provide signals that indicate whether
an aircraft is above, below, or in-line with the glide path to a runway and
enables a pilot to adjust the aircraft up or down correctly during landing. This
is the same type of information as provided by the ILS Localizer, but for the
vertical reference rather than the lateral/horizontal reference; the same
modulation and antenna techniques are used. This vertical correction is
performed using two AM signals with an AM depth of 40%, operating at a
carrier frequency range between 329.90 to 334.70 MHz.
For an aircraft on approach, using the ILS Glide Slope to land on a runway, the
upper signal is modulated at a frequency of 90 Hz AM by default, and the
lower 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 and 150 Hz amplitude modulation.
