34-57-00

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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737-300/400/500MAINTENANCE MANUAL
 B.  The control panel has two frequency indicators, two sets of frequency selection knobs, a mode switch, a TONE-OFF switch, a GAIN control, a transfer switch (TFR), and two transfer indicating lights.
 C.  The mode switch controls and indicates the operating mode of the respective ADF receivers. The TEST position of the mode switch is a momentary contact position and controls the receiver self-test function.
 D.  The TONE-OFF switch controls operation of the tone oscillator in the ADF receiver. The GAIN control adjusts the level of audio from the receiver to the flight interphone system.
 E.  The transfer (TFR) switch allows a second frequency to be preselected while the system is in operation. When the TFR switch is operated, the system will change to the preselected frequency. The frequency indicator of the selected receiver will be brighter than the inactive indicator.
 F.  The control panel is mounted on the flight deck in the aft electronic control panel.
 9.  Radio Digital Distance Magnetic Indicator_________________________________________
 A.  A radio digital distance magnetic indicator (RDDMI) is installed on each pilot's instrument panel. Each RDDMI displays airplane compass heading, VOR or ADF bearing, and DME distance.
 B.  Compass heading from the inertial reference system is used to position the compass card through a servo drive system.
 C.  The radio bearing display consists of two concentrically mounted pointers: one wide and one narrow. The two pointers can display radio bearing information for two ADF or two VOR stations with the compass card taken as reference.
 D.  ADF system No. 1 information is displayed by the narrow pointer while ADF system No. 2 information is displayed by the wide pointer of each RDDMI.
 E.  Heading and bearing pointer warning flags monitor the validity of the ADF bearing displays.
 F.  For additional description, operation, and maintenance instructions applicable to the indicators, refer to AMM 34-28-00, IRS; AMM 34-31-00, VOR/ILS, and AMM 34-55-00, DME.
 10. Operation (Fig. 2 and 3)_________
 A.  Collins 51Y-7 ADF Receiver
 (1)  
The ADF system operation consists of two modes of operation: an operational mode and a test mode. The operational mode is the normal operation of the ADF receiver using antenna signals. The test mode uses only internal signals to assure operation of the receiver.

 (2)  
Operational Mode

 (a)  The rf signal is coupled from the directional fixed loop antenna through the quadrantal error corrector to the goniometer in the receiver. The angular position of the goniometer rotor determines the input amplitude and phase to the loop rf amplifier. The loop rf amplifier output is applied to the balanced modulator where the signal is modulated at 90 Hz by the switching oscillator. The balanced modulator output is double-sideband, suppressed-carrier signal.
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 34-57-00
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
 (b)

(c)

(d)

(e)

(f)

(g)

(h)

A
737-300/400/500MAINTENANCE MANUAL
The sense signal originating in the sense antenna is transferred through the sense antenna coupler to the sense rf amplifier where the signal is amplified and applied to the signal mixer. The signal mixer output is a phase modulated signal with a 90 Hz modulation frequency. The direction and phase is determined by the difference between the rotor position of the goniometer and the null directional of the station.The amplified loop and sense antenna signals are coupled through a 0.19 to 1.75 MHz bandpass filter to the first rf mixer and heterodyned with the frequency synthesizer (vco) output. The first rf mixer signal is then applied to the 15 MHz crystal filter. The 15 MHz crystal filter output is routed through the agc attenuation circuit to the 15 MHz IF amplifier. The agc attenuator and 15 MHz IF amplifier are gain controlled by the agc amplifier.The second mixer inputs are 15 MHz from the IF amplifier and
 18.6 MHz from the vco. From the second mixer, the 3.6 MHz difference frequency is filtered, amplified and applied to the bearing detector for phasing information. The detector output is applied to the servo-phase detector along with 90 Hz from the switching oscillator to be amplified and applied to the loop servomotor for nulling the goniometer. Also, the detector applies outputs to the audio compressor and the agc amplifier. The audio compressor signal is amplified and applied to the flight interphone system (AMM 23-51-00).The loop servomotor also drives the bearing synchro which applies outputs to the loop antenna position indicator on the front of the ADF receiver and also the bearing indicator on the RDDMI's.The TONE switch allows for a BFO tone (1020 Hz) to be injected into the 3.6 MHz IF amplifier. When a CW station is being received, the 1020 Hz output can be heard in the flight interphones. If the ON position is not selected when receiving a CW station, the 1020 Hz signal will not be heard.The mode switch on the ADF control panel allows selection of the ADF or ANT positions. In the ADF mode, both the loop and sense antenna are used to give an output to the bearing indicator (RDDMI) and the flight interphone system. In the ANT mode, the sense antenna is used to receive a station and is only used for monitoring the audio of the station selected.Frequency selection is accomplished with the use of the frequency selector knobs on the ADF control panel. BCD (binary coded decimal) information is fed to the vco and the band logic circuits. The BCD signals are changed to an incremental voltage and applied to the bandpass filter to change the frequency receiving characteristics.
　
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