Signal Processor

The signal processor gets bearing information from the

receiver/processor and changes it to digital signals. The

signal processor does these functions:

• Uses time measurement logic and the bearing information to calculate the intruder airplane range and bearing

• Detects the mode C or mode S pulses

• Controls the suppression circuit to send the suppression

pulse when TCAS transmits

• Makes all signals necessary to receive and transmit mode S and ATCRBS interrogations through the receiver/transmitter circuits.

Suppression

The suppression circuit sends a suppression pulse when the TCAS computer transmits. The TCAS computer receives a suppression pulse when an onboard ATC transponder or DME interrogator system transmits. This suppression pulse stops the TCAS computer receiver and transmitter circuits.

Speech Processor

When there is a TA, RA, or during a self-test, the TCAS computer sends signals to the speech processor. The speech processor sends the aural alerts to the REU. The REU sends them to the flight compartment.

During aural annunciations the GPWC sends an analog discrete to the TCAS computer to prevent TCAS advisories.

During predictive windshear annunciations the weather radar sends an analog discrete to the TCAS computer to prevent TCAS advisories.

Receiver Processor

The receiver gets the target replies from the antennas. The receiver uses the phase of the received signals to determine the bearing of the target. The receiver sends the signal to the signal processor to calculate the range to the target. The receiver decodes the target altitude from the reply signal. The receiver also receives and decodes coordination replies from targets equipped with TCAS.

Transmitter

The transmitter has a 1030 MHz output. The transmitter gets signals from the signal processor. The transmitter sends the formatted signals to the beam steering and attenuator (ATT) circuits. The transmitter controls the beam steering circuits and whisper/shout attenuator.

Beam Steering and Attenuator Circuits

The beam steering circuits send the signals to the four antenna elements. During transmit, the beam steering circuit controls the phase relationships of the four RF outputs. The whisper/ shout attenuator makes the output power smaller or larger based on the control signals from the transmitter.

During receive, the phase of the received signals is different in each element. These beam steering circuit sends the signals to the receiver.

The TCAS computer receives a discrete input from the landing gear lever switch. When the landing gear lever is down, the TCAS computer uses all four antenna elements equally for the bottom antenna. Thus, the bottom antenna operates as an omnidirectional antenna.

BITE

The TCAS computer has BITE. The BITE continuously monitors TCAS for system faults and interface faults during normal operation. Also, when you start a self-test, the BITE makes test signals and sends them to the signal processor and receiver/ transmitter circuits. The BITE monitors for system faults and interface faults during the self-test.

When the BITE detects a fault through the continuous fault monitor, the fault goes into the fault memory. It also goes to the I/O circuits for output to the CDS DEUs and the FDAU.

When the BITE detects a fault during a self-test, the fault data goes to the I/O and then to these systems:

• DEUs

• REU* FDAU

• TCAS computer status LEDs if test is done from computer front panel.