368 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
To set the ILS Localizer phase of the right signal relative to the left
1. Press Aux Fctn > Avionics > ILS Localizer
2. Press Left/Right Phase
(Default <value> is 0.00 deg.)
3. Select a <value> from 0.00 deg - 360 deg and press Enter.
These softkeys set the phase of the right (150 Hz) ILS Localizer signal relative
to the left (90 Hz) ILS Localizer signal.
To set the ILS Localizer DDM polarity to fly left or fly right
1. Press Aux Fctn > Avionics > ILS Localizer
2. Press DDM/SDM
3. Press Fly Left | Right
(Default selection is Left.)
4. Select either Left | Right
These softkeys set the “Difference in Depth of Modulation” (DDM)
polarity of the ILS Localizer signal to either:
LEFT = positive | RIGHT = negative
The ILS Localizer provides signals that indicate whether an aircraft is Left,
Right, or in-line with the glide path to the runway and enables a pilot to adjust
the aircraft Left or Right correctly during landing. This lateral/horizontal
correction is performed using two AM carriers with an AM depth of 20%,
operating at a carrier frequency range between 108.10 - 111.95 MHz.
For an aircraft on approach, the left signal is modulated at a frequency of 90 Hz
by default, and the right signal is modulated at a frequency of 150 Hz by
default. When an aircraft is in-line with the glide path to the runway, the
amplitude of the 90 Hz and 150 Hz sine-wave signals are equal. Left or right of
this glide path, the amplitudes are different.The difference in amplitude can
determine the relative position of an aircraft from this theoretical glide path.
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 the 90 Hz modulation and the
150 Hz modulation.
DDM is defined to be the “percentage modulation depth of the larger signal”
minus the “percentage modulation depth of the smaller signal”,
divided by 100.
DDM = [AM(90 Hz)% - AM(150 Hz)%] / 100
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