VOR MODULATION

TM 11-6625-2976-40

Closing the front panel LOC 1020 HZ switch enables the MB vco to apply 1020 Hz audio signal through

the LOC output amp to amplitude modulate the composite LOC rf output signal.

GS Mode Selection. In addition to the GS 90 Hz and 150 HZ DELETE modes, test set provides the

following GS operational modes:

1. On-course (GS OC)

2. Variable (GSVAR)

3. Up/down (GS UP/DOWN)

The GS on-course and variable modes function much the same way as corresponding LOC modes.

The 90 Hz and 150 Hz GS signals are directed by the appropriate GS front panel switches through the

circuit card assembly's GS OC or GS VAR and the GS output amp to GS/UHF rf module A2.

The GS up and down modes function in the same manner as LOC left and right modes. The 150 Hz (up)

or 90 Hz (down) signal is directed by the appropriate GS UP/DOWN front panel switch through the cir-

cuit card assembly's GS UP/DOWN SELECT and GS output amp to GS/UHF rf module A2. Test point J1

provides a check of the GS output modulated signals.

VOR MODULATION

Refer to FO-6 while reading the text in this section.

Operating voltage is applied to the VOR modulating circuits in the circuit card assembly and VOR rf

module A5 by closing front panel switches S2, S18, S22 and S21. See paragraph 1-14 for a

discussion of DC Power Distribution.

The VOR modulating circuits use all three frequencies generated by the 3.932 crystal oscillator and

frequency divider. The 30 Hz signal is applied to a phase shift network and phase (bearing) select

switches in the circuit card assembly. The 240 Hz signal provides a clock pulse for the phase shift

network, which uses this signal to produce seven 30 Hz phase difference signals. These signals

correspond to 45 through 315 degrees in 45-degree increments.

Eight signals, seven produced by the phase shift network and 000 in-phase 30 Hz signal, are applied

to the phase (bearing) select switches. The bearing signal selected by the front panel VOR bearing

select switch (S17) determines which one of these signals will be activated. The 180-degree bearing

signal is taken as the reference 30 Hz and applied to one path through the 30 Hz VAR/REF DELETE

switch.

The circuit card assembly variable/reference delete switch is controlled by three front panel switches:

1. VAR 10 switch S25

2. 30 VAR DELETE switch S19

3. 30 REF DELETE switch S20

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