User's Manual

Model 1150A DVOR
2-22 Rev. - November, 2008
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is approximately 10K ohms with the amplifier at 25 degrees C. R108 has a negative temperature coefficient,
meaning as the temperature of the heat sink rises, the resistance of R108 reduces. In the event of excessive heat sink
temperature, the output of comparator U23:B will travel to a low state. When the comparator goes low, this will
make Q2 stop conducting, disabling transmission. The comparator will not reset until the temperature of the heat
sink cools down. The over temperature shutdown signal is also sent to U9:B for monitoring purposes.
The amplifier assembly contains four different local power supplies that are converted from the +48Vdc nominal
input. The power supplies are: +15Vdc, +10Vdc, +5Vdc, and +3.3Vdc. The +15Vdc supply is directly converted
from the +48Vdc input. R45 and R47 along with U14 set the output voltage for the +15Vdc supply. The +15Vdc
supply is a switching supply only used to convert the +48Vdc input to a level suitable for linear regulation of the
+10Vdc supply. From the +10Vdc supply, the +5Vdc supply is linear regulated and the +3.3Vdc linear regulates
from the +5Vdc supply.
All power supplies within the module are monitored with voltage comparators U18A, U18B, U18C, U18D, U19B,
U19D, U20C, and U20D. The comparator circuits are powered directly from the +48V input through R51, R52, and
CR10. Diode CR10 provides a +10Vdc reference for powering the comparator IC’s and providing a reference
voltage for the voltage divider resistors. The power supply monitor circuit is the only circuit in the module
assembly that is not fused. This was intentional for monitoring the power supplies without degrading performance
in the power supply monitoring circuit. A logic low on any of the power supply monitoring comparators will cause
the output of U19:A to travel to a high impedance state. This will prevent the power ok LED (CR11) from
conducting. Comparator U19:C will also travel to a high impedance state for monitoring the power supplies
externally.
2.3.2.5
Bi-Directional Coupler (1DC1)
The Bi-Directional Coupler is used to obtain a representative sample of the forward and reflected RF powers of the
carrier signal (refer to Figure 2-2, DVOR system block diagram). The coupler has negligible insertion loss between
the input and output connectors. Internal directional pickup loops couple a portion of the forward and reflected
powers to the output sampling ports. These ports provide a fixed ratio of the sampled powers to the RF monitor
assembly for detection and analysis processing.
2.3.2.6
Sideband Generator Assembly (1A4A1, 1A4A2, 1A4A6, 1A5A7)
The DVOR uses two Sideband Generator Assemblies for each transmitter system. Each generator contains one
sideband amplifier CCA part number 012218-0001. The Sideband Generator may be plugged into one of four
positions within the DVOR cabinet. Position 1A4A1 is for transmitter 1 Sidebands 1 and 2 signal generation of two
lower sideband outputs (Carrier -9960 Hz). Position 1A4A2 is for transmitter 1 Sidebands 3 and 4 signal generation
of two upper sideband outputs (Carrier +9960 Hz). Position 1A4A6 is for transmitter 2 Sidebands 1 and 2 signal
generation of two lower sideband outputs (Carrier -9960 Hz). Position 1A4A7 is for transmitter 2 Sidebands 3 and 4
signal generation two upper sideband outputs (Carrier +9960 Hz).
2.3.2.6.1
Sideband Generator Assembly Block Diagram Theory
Refer to Figure 2-10. The Sideband CCA (PN 012218-0001) is responsible for developing the sideband amplitude
modulated signals that are sent to the commutator. The commutator only acts as a selection switch to the sideband
antenna array and performs no modulation.
RF enters the Sideband Generator at P1D from the frequency synthesizer upper or lower sideband output. The signal
is CW and at approximately 0 dBm. The signal is split and then enters either sideband 1 or sideband 2 circuits. The
two sidebands are identical so only one will be described.
After the RF splitter the CW signal enters the manual phaser. This phaser is controlled with an operator setting in the
PMDT. This phaser is used to align all four sidebands in a DVOR to the same RF phase in order to get maximum
sideband modulation. The signal then passes through a buffer and then enters the bi-phase modulation. The bi-phase
modulator can be set to provide 0 or 180 degrees of RF phase shift. In a DVOR this is directly controlled by J11.
This jumper allows for either a setting of 0 or 180 degrees based on the frequency of operation and described in the
alignment procedures.