IB ALL  CONFIG 3  01 Page 10  Dec 25/8734-53-00
 On IB 406 and on,
 (16)
 The ATC system receives pulse-coded interrogations in one of three modes as determined by the spacing between the pulses. Modes A and B are used for air traffic identification; mode C is used for automatic altitude reporting.

 (17)
 Interrogation signals detected by the ATC system are analyzed to determine their mode and source. Either the main lobe or side lobe of the ground station radar may contain interrogations, but only main lobe interrogations are accepted. If the mode matches the mode of the interrogation, the signals are accepted and a reply is transmitted. When the altitude reporting switch is turned on, mode C interrogations are accepted. If the altitude reporting switch is turned off, mode C interrogations are not accepted.

 (18)
 Each reply pulse train consists of zero to 12 pulses within two framing pulses. When the identification button is pressed, an identification pulse follows the second framing pulse for several transmissions. For mode A replies, the number of pulses in the pulse train is determined by the identification code selected on the control module. For mode C replies, the number of pulses is determined by the presence or absence of altitude data from the Air Data Pressure Instruments (Ref 34-13-00).

 (19)
 Received signals from the antenna are routed through the Diplexer/Low Pass Filter and applied to the Preselector/Mixer (Fig. 3). In the preselector the signal is passed through a bandpass filter tuned to 1030 MHz. The filter output is mixed with 970-MHz local oscillator (L.O.) signal. The 60-MHz IF signal from the mixer is applied to the IF amplifier/detector module where it is amplified and detected. The output of the IF amplifier/detector is applied to the video processor where it is amplified, pulse shaped, filtered by a noise suppression circuit, and side lobe suppression is performed. The signal is then sent to the decoder/encoder circuitry. The decoder/encoder chip decodes the received message, determines whether Mode A, Mode B or Mode C data is requested and then develops the appropriate serial data output to be applied to the transmitter.

 (20)
 The modulator accepts the decoder/encoder serial data outputs, adjusts the amplitude and width of the pulses and supplies the proper signal to the transmitter modulator circuit. The modulator also receives and sends suppression pulses to the DME system (Ref 34-55-0). The suppression pulses prevent simultaneous transmission of ATC and DME signals. The modulation signal modulates the transmitter oscillator which is a 1090-MHz cavity controlled pulsed oscillator. The output of the transmitter oscillator is approximately 1.5 watts peak RF power. The pulsed RF signal is applied to the exciter module, amplified to 150 watts peak RF power then used to drive the power amplifier module where the RF signal is amplified to 500 watts peak RF power. The power amplifier output is then sent to the diplexer to be routed to the antenna.

 EFFECTIVITY

 IB ALL  CONFIG 3  01 Page 11  Apr 25/8034-53-00
 (21) Upon activation of the test switch on the receiver transmitter (R/T)
 front panel, the functional test module will generate an RF pulsed
 signal. This signal is applied to the local oscillator module where
 60-MHz sidebands are generated. These sidebands are a pulsed pair
 which are properly spaced to represent a valid mode interrogation.
 The L.O. signal is applied to the mixer and a 60-MHz IF signal is
 generated. From this point on the signal is processed as a valid
 interrogation and the light on the R/T front panel will be
 activated. The R/T light will go out immediately when the R/T
 switch is released.
 B.  Control
 (1) Turn On Procedure
 (a) Turn on airplane electrical power. Refer to 24-22-00.
 CAUTION: ENSURE THAT EQUIPMENT COOLING SYSTEM IS OPERATING_______
 BEFORE TURNING ON ELECTRICAL OR ELECTRONIC SYSTEMS OR
 HEAT DAMAGE COULD RESULT. EQUIPMENT COOLING SYSTEM
 MUST BE SET FOR NORMAL COOLING AS DESCRIBED IN 21-
58-00.
 (b) Close following circuit breakers on electronic circuit breaker
 panel P7.
 XA  ATC 1 AC
 XA  ATC 2 AC
 (c) Select ATC transponder 1 or 2 as desired using ATC switch on
 control module.
 XA  (d) Set function selector on ATC control module to OFF.
 (e) Set function selector to STBY and wait 1 minute or longer.
 (f) Set function selector to A or B as desired.
 NOTE: The function selector may be turned immediately from____
 STBY to A or B, however, there may be an automatic
　
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