Interrogator Functional Description

Aviation Electronics Technician 1 (Organizational)
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SIF reply code is identical to the code switch settings. There are two indicators (FAULT and CHAL) that indicate correct operating status of the system. The mode 4 alarm may be overridden by using the toggle switch M4 ALARM OVERRIDE. RECEIVER-TRANSMITTER RT-868A/ APX-76A(V).— The receiver-transmitter (fig. 3-23) takes the mode 1,2, 3/A, or 4 interrogation and ISLS pulses and modulates a 1030 MHz carrier wave with them. This is the transmitted signal from the interrogator set. The transponder reply signal, at the reply frequency of 1090 MHz, is amplified, detected, and processed by the receiver section. The reply video is then sent to the radar set for display on the various indicators. There are three fault flags on the front of the RT that indicate malfunctions in one of the three functional sections of the receiver-transmitter. SWITCH-AMPLIFIER SA-1568A/APX-76A (V).— The switch-amplifier (fig. 3-24) switches the interrogator’s RF output from the sum antenna channel to the difference antenna channel for the duration of the ISLS pulse. During this time, the output is amplified by 4 to 7 dB. This amplification provides the required antenna output characteristics. ELECTRONIC SYNCHRONIZER SN-416A/ APX-76A(V).— The synchronizer (fig. 3-25) generates the initiation and interrogation cycles. The synchronizer provides a functional link between the Figure 3-23.-RT-868A/APX-76A(V) receiver-transmitter. Figure 3-24.-SA-1568A/APX-76A(V) switch-amplifier. radar trigger generation and the radar modulation circuits. COMPUTER KIR-1A/TSEC.— This computer is used for mode 4 security and decoding for secure operation. Interrogator Functional Description The IFF interrogator challenges and identifies properly equipped targets on the display groups. It challenges in modes 1, 2, 3/A, SIF, or mode 4. Target responses are shown on the display group next to the target in the form of numbered cues. MODES 1, 2, AND 3/A TRANSMISSION.— When the TEST-CHAL CC switch on the interrogator control box is set to the CHAL CC position, the interrogation cycle is initiated and lasts for 5 to 10 seconds. The basic radar trigger is applied to the Figure 3-25.-SN-416A/APX-76A(V) synchronizer. 3-21

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