Operating instructions

AVIONICS SYSTEM
B-9
Note
With the localizer screen displayed, using the FREQ [⇑] or [⇓] increment keys will step the
carrier frequency up or down to the next allocated localizer frequency. The corresponding
glideslope frequency will be set if the glideslope screen is selected
With the glideslope screen displayed, using the FREQ [⇑] or [⇓] increment keys will step up or
down the localizer frequency table, but with the glideslope frequency displayed.
Setting the RF level
To change the RF level first press the [RF Level] key, then enter the required level using the data
entry keys or use the variable control to adjust the displayed frequency. See RF frequency and
level on page B-8.
Setting the SDM (Sum of Depth of Modulation) level
The position indication on the ILS receiving equipment is determined by measurement of the
difference between the modulation depth of the 90 Hz tone and the modulation depth of the
150 Hz tone. Localizer transmission specifications call for 20% modulation levels for each tone
giving an SDM value of 40%. Glideslope transmissions require 40% modulation for each tone,
giving an SDM level of 80% modulation.
These levels are default settings for the Service Monitor and are always called up when the [Loc]
or [G.S.] keys are pressed.
To change the SDM level press the [SDM] key to show ‘SDM’ in reverse video. Either key in the
digits of the percentage value using the data entry keys and the % terminator key or use the
variable control knob to set the new level.
The maximum SDM which can be set when localizer test is selected is 50 %. When glideslope is
selected, the maximum SDD level is 90 %.
Setting the DDM and selecting Fly Right / Fly Left / Fly Down / Fly Up indications
To test the indicating functions of an ILS receiver, the difference in depth of modulation of the
two tones must be varied.
When the 90 Hz tone predominates the indicator will show ‘Fly Right’ or ‘Fly Down’; when the
150 Hz tone predominates the indicator will show ‘Fly Left’ or ‘Fly Up’.
On the ILS displays of the Service Monitor, a digital read-out of the DDM level is shown in the
left half of the display and a graphical indication on the right.
The DDM level of the test signal can be set, changed or varied as required.
Using the [DDM] key
Pressing the [DDM] key will highlight the DDM legend on the display. A new level can be
entered using the data input keys and the [%] terminator key or by adjusting the value by using the
variable control.. The new level will be shown on the display and the graphical indication will
adjust.
Pressing the [Fly Lft/Rt] key (or the [Fly Up/Dn] key) will change the relative depth of the
modulation to simulate ‘Fly left’ or Fly right’ (or ‘Fly up’ or ‘Fly down’) conditions.