Aviation Electronics Technician 1 - Historic Naval Ships Association

operates at 38 Hz. The lobing action prevents theantenna system from being blanked out during aircraftmaneuvers.TRANSPONDER SET CONTROL C-6280(P)/APX.— The IFF control box (fig. 3-17) provides theIFF transponder operational and test controls. TheIFF transponder control box controls the transponderin any of the five modes: modes 1, 2, 3A, C, and 4.Figure 3-16.-SA-176/A RF transmission line switch.RECEIVER-TRANSMITTER RT-859/APX-72.— The receiver-transmitter (fig. 3-18) willprocesses valid IFF interrogations and provides codedpulse train replies to give automatic radaridentification of the aircraft in one of five modes. Thefive modes are discussed later in this chapter.The transponder set also provides the SelectiveIdentification Feature (SIF) to permit a specificaircraft to be selected from other properly respondingaircraft.Major ComponentsThe transponder set consists of four main boxesand a test set. These components will be discussed inthe following text.RF TRANSMISSION LINE SWITCHSA-1769/A.— The RF transmission switch (fig. 3-16)alternately connects the transponder set to the top orbottom UHF L-band antenna. This switching (lobing)Figure 3-17.-C-6280(P)/APX transponder control box.Figure 3-18.-RT-859/APX-72 receiver-transmitter.3-16