User Manual

system components 523-0809018
2.8.6.6. The data bus input through an ARINC 429 high-speed receiver to the third input UART is read from the UA RT by the
microprocessor.
2.8.6.7. The processor reads the discrete inputs through two buffer circuits. The first buffer provides the i nput port A/B select
logic, strut switch logic, source identification logic, maximum airspeed logic, altitude input l ogic, and TCAS installed logic.
2.8.6.8. Parallel d ata i s output from the microprocessor to the output UARTs. Both UARTs are enabled by the processor to decode
and transmit serial data.
2.8.6.9. The TDR is interrogated b y the 3-pulse Side-Lobe-Suppression (SLS) method. The TDR-94D operates with one antenna
to provide TC AS air-to-air capability. The 1030-MHz interrogation input is received on the L-band antenna, low-pass filtered,
and applied through the transmit/receiv e switch to the front end receiver. The transmit/receive switch con nect s the antennas to the
receiver, but not the transmitter, in receive mode.
2.8.6.10. The front end receiver is a dual 1030-MHz bandpass filter that rejects images and spurious responses. The two fil tered
rf inputs are then independently mixed with a 1090-MHz injection frequency from the synthesizer. This local oscillator frequency is
programmed by the microprocessor using latched data, clock, and enable logic. The two resultant 60-MHz if signals are amplified
and applied to the Differential Phase Shift Keying (DPSK) detector and the video processor.
2.8.6.11. The DPSK detector is a part of the receiver circuit that senses phase reversals present in mode-S interrogations. The
DPSK detector outputs are applied to the Pulse Amplitude Modulation (PAM ) decoder. The video processor m onitors the received
signal strengths and generates video signals to the PAM decoder.
2.8.6.12. The PAM decoder and a dedicated video microprocessor function together as an interrogation processor. This circuit
processes the video inputs t o determine if the received interrogation is a valid ATCRBS or Mode-S interrogation. If a response
is required, the processor determines if the t op or the bottom antenna should be used for the reply. The processor then enables the
transmit mode and generates the proper response. The TCAS generated collision avoidance transmit data is input to the interrogation
processor through the dual port RAM.
2.8.6.13. When transmit mode is enabled by the interrogation processor, INT SUPRN logic activates the suppression amplifier and
XMT ENBL logic activates the transmit enable driver. During transmit mode, the suppression amplifier momentarily inhibits other
L-band units, described in a later paragraph. During transmit mode, the enable dr iver closes the transmit/receive switch. This isola tes
the receiver and connects the transmitter to the selected antenna. The interrogation processor generates the ATCRBS or Mode-S
reply output and top/bottom antenna select logic. This response is applied through a multiplexer to the rf transmit modulator.
2.8.6.14. The 1090-MHz transmitter circuit consists of an rf modulator and a power amplifier. The rf modulator receives operating
power from the high-voltage power supply. This power supply provides the voltage levels required for L-band transmission. A
current monitor disables both the rf modulator and the High-Voltage (HV) supply if the current draw or power output becomes
excessive. An HV power monitor provides a high-power monitor output through a buffer to the main microprocessor.
2.8.6.15. The reply output from the interrogation processor controls the modulator bias applied to the power amplifier. The power
amplifier is driven by a 1090-MHz CW signal generated by the synthesizer. The ON/OFF BIAS from the modulator causes the
power amplifier to generate a corresponding pulse train output, at the 1090-MHz drive frequency. This rf reply output is a series of
pulses, the number and spacing of which is determined by the ATC code plus a trailin g IDENT pulse, if selected, and the ope rat ing
mode. The pulse transmission is applied throug h the closed tran smit/receiv e switch and radiated out the antenna. The transmit signal
is sampled by a forward power monitor, which provides a low-power monitor output through a buffer to the processor.
2.8.6.16. A suppression amplifier generates a blanking pulse output when t he interrogation processor selects transmit mode.
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