User's Manual

Model 1150A DVOR
Rev. - November, 2008
This document contains proprietary information and such information may not be disclosed
to others for any purposes without written permission from SELEX Sistemi Integrati Inc.
2-75
To simplify the interconnection of the signals and antennas used in the 48 antenna system, Ta
ble 2-1 is available as
an aid.
Each individual antenna switch circuit on a Commutator CCA is functionally identical with the others. Pin diodes
are used to perform the active switching of the RF to the individual antennas, and to swap the LSB and USB signals
between each half of a switch assembly.
Each Commutator CCA can be thought of as having two halves, each half is connected to twelve antennas. One half
is energized by the LSB sin RF and the other half by USB sin RF. The condition of the transfer and NOT transfer
lines (from the driver board) determine which half of the Commutator CCA the LSB and USB RF signals are
connected.
Each antenna switch on each half is applied RF energy via a common bus. The transfer control switches the two RF
signals between the two bus lines, while maintaining complete isolation between them. The pin diode switches are
operating with either +5V or -10V applied, to insure the diodes are either fully on or off.
When the XFR line is HIGH (+5 Vdc), the NOT XFR line is LOW (-10 Vdc). This forward biases diodes CR301,
CR302, CR305, CR308, CR311 and CR312. Diodes CR303, CR304, CR306, CR307, CR309 and CR310 are
reversed biased. This allows the LSB RF signal to flow through CR311 and CR308 and apply RF to the “A” bus
switches. The USB RF signal goes through CR302 and CR305 to the “B” bus antenna switches. Note that CR306
and CR307 are both biased off which provides isolation, while at the same time CR301 and CR312 are biased on to
insure any RF in that portion of the circuitry will be shorted to ground.
When the XFR and NOT XFR signal switch, the LSB RF signal is applied to the “B” bus via forward biased diodes
CR307 and CR310; the USB RF signal is sent to the “A” bus via forward biased diodes CR303 and CR306.
To enable the RF energy to be selectively applied to an individual sideband antenna, and at the same time prevent
parasitic re-radiation from an adjacent antenna, a pin diode antenna switch is used. The drive levels are similar
(+5V, -10VDC) to the transfer levels used to switch the LSB and USB RF energy.
Each antenna assembly has twenty-four switches. Twelve are connected to the “A” bus and twelve to the “B” bus.
Display driver U8 on the driver board drives both the 1A and 14B positions; display driver U13 handles both the 2A
and 15B positions, etc. (see Table 2-1). This allows opposite paired antennas to radiate the LSB and USB signals.
Each display driver provides two switchable outputs to each antenna pin diode switch. For simplicity, the discussion
is limited to the 1A switch circuits. Each antenna pin diode switch circuit has a different reference designator series,
starting with 10 and incrementing in groups of 10. Refer to the schematic for all of the group reference designators.
When display driver U8 is selected, the 1A ON line has +5 Vdc applied to it and the 1A OFF line has -10 Vdc on it.
This forward biases diodes CR12 and CR14 and reverse biases diodes CR11 and CR13. If LSB RF energy is on the
A bus, it will travel through diodes CR12 and CR14 and be applied to the sideband RF cable that feed that sideband
antenna.
If U8 is not selected, then the 1A ON line has -10 Vdc on it and the 1A OFF line has +5 Vdc on it. This forward
biases diodes CR11 and CR13 and reverse biases diodes CR12 and CR14. CR14 blocks RF energy from the A bus
from traveling through the switch circuit. CR11 will pass any RF energy that may appear on the antenna feed cable
to 47 ohm resistor R11. Capacitor C12 is a low impedance path at RF frequencies; therefore, resistor R11 is
effectively shorted to ground. Each antenna that is not radiating an RF signal is now connected to an on-board
dummy load. Additionally, any RF that may leak through CR14 will pass through CR13 to ground also via
capacitor C15. Each antenna line is protected from extreme voltage spikes caused from lightning or other EMF
generators by a gas surge suppressor.