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AVIONICS SYSTEM

B-3

The simulated localizer signal

B2142

Fig. B-1 ILS screen and menu

The simulated localizer signal from the Service Monitor can be set to any of the ILS localizer

carrier frequencies between 108 and 112 MHz The carrier is amplitude modulated by signals of

90 Hz and 150 Hz. The Service Monitor ILS display screen and menu gives a graphic and digital

readout of the parameters relating to the simulated signal. The soft key menu allows the

parameters to be adjusted either directly or by using the data input keys or the variable control.

The localizer and glideslope carrier frequencies are inter-related. See

ILS Frequency Pairing,

below.

The depth of modulation provided by each generator is variable to simulate the position of the

aircraft relative to the center line, with a horizontal bargraph giving a representative display on the

screen. Each modulating signal can be disabled so as to test the operation of the ‘beam lost’ flag

alarm.

When the [Ident] key is pressed the localizer carrier is amplitude modulated with a tone of

approximately 1.02 kHz to simulate the voice/identity signal. The depth of modulation of this

signal is adjustable.

The localizer position signals from the Service Monitor are disabled when the Ident facility is

active.

Glideslope signal

The glideslope used by an aircraft approaching the runway is at a defined angle and is

electronically prescribed by transmissions from a pair of antennas in a similar manner to the

glidepath localizer transmissions.

The twin lobes are set to radiate at an upward angle from the runway threshold and overlap along

the glideslope. The lower lobe transmits the carrier with 150 Hz amplitude modulation and the

upper lobe with 90 Hz amplitude modulation. The RF frequency band allocated to glideslope

transmitters is from approximately 328.5 to 336 MHz. See

ILS Frequency Pairing, below.

The simulated glideslope signal

This signal from the Service Monitor is similar to that generated to simulate the localizer

transmissions. The parameter settings can be controlled in the same way. A vertical barchart

provides the position relative to glideslope indication.

The glideslope and localizer carrier frequencies are inter-related. See

ILS frequency pairing,

below.

The ident function is not applicable to glideslope transmissions.

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Aeroflex 2948B Betriebsanleitung Seite 248