_
NC
ANT

OFF
P6 CIRCUIT BREAKER PANEL
OFF
ADF

ANT
THOU-A B C D A B C D A B C D
TENTHS
TEST ADF
SANDS HUNDREDS BCD TENS BCDUNITS BCD
LEFT FREQUENCY SELECT GAIN T172 OFFD71 AUDIO FLT INPH SYS
HV D71
W
INSTR ANT
(23-51-00)XFMR 1
LV H THOU-ABCDABCDABCD
ADF TFR TENTHS
26V AC
GND
SANDS HUNDREDS BCD TENS BCDUNITS BCD
TEST RIGHT FREQUENCY SELECT
(E1-2)
A
TFR
FROM B
TONE
P8 PANEL

10
205
0
1255
OFF ON
OFF ON
LIGHTING

A
1 TEST INDICATIONS ARE
D ANT ADF
F OFF TEST
TONE
W W
CONTROL P
RDDMI POINTER TO 315 |5 DEGREES1.5V AC
GAIN
(RELATIVE TO LUBBER LINE)(33-11-00)
W W
 1020 HZ AUDIO TONE OUTPUT2.M
45 DEGREE GONIO METER INDICATION3.
 ON RECEIVER FRONT PANELADF-2 CONTROL PANEL (P8)
ADF System Schematic
Figure 3 (Sheet 2)

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 34-57-00
 ú ú 12 Page 7 ú Nov 12/01

BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
 3.  Quadrantal Error Corrector
__________________________
 A.  The airplane wings and fuselage interact with the field of an incoming rf signal to distort the reception pattern. The quadrantal error corrector compensates the loop antenna signal through fixed attenuators which remove this pattern distortion (quadrantal error) from the incoming rf signals. The error corrector then couples the corrected rf signals into the loop antenna transmission cable.
 B.  The quadrantal error correctors are mounted directly on top of the loop antennas inside the loop antenna mounting cavities. Removal as individual units is possible only after the respective loop antenna has been removed.
 4.  Loop Antenna Transmission Cable
_______________________________
 A.  The corrected loop antenna rf output is transmitted from the loop antenna cavity to the receiver by the loop antenna transmission cable. This cable consists of a bundle of four twisted coaxial transmission lines in a sheathed cover.
 5.  Sense Antenna
_____________
 A.  Two ADF sense antennas are installed, one on the left wing-to-body fairing and the second on the right wing-to-body fairing. The antennas are located aft of the aft wheel well bulkhead at station 727B. A metal coating on the fairings is used as the antenna element.
 B.  The sense antennas provide a nondirectional reception pattern and high signal strength to the receivers.
 6.  Sense Antenna Coupler
_____________________
 A.  A coupler is used in each of the ADF systems to match the capacitance of the sense antenna to the capacitance of the transmission line between the antenna and the receiver. The coupler contains the necessary circuits to provide optimum performance. The total capacitance of the sense antenna, coupler, and line, as seen by the receiver input, is approximately 3000 pF.
 B.  The couplers are mounted near their respective sense antenna at station 727B, waterline 160 and buttock line 45.
 7.  Receiver
________
 A.  The receiver is a transistorized, superheterodyne radio receiver that processes amplitude-modulated, rf signals within the frequency range of 190 to 1750 kHz, and produces a synchro output representing relative compass bearing to the rf transmitter site. It also produces an audio output from any modulation on the received rf signal for use in the flight interphone system.
 B.  A system test switch and test indicator are located on the front panel of the receiver. The test switch activates the functional test circuits in the receiver. The test indicator is part of the goniometer/syncho system and provides a 45-degree self-test indication when the test switch is pressed.
 C.  Both receivers are mounted on shelf No. 4 of electronics equipment rack E2.
 8.  Control Panel
_____________
 A.  The ADF control panel remotely controls all receiver functions and operating modes. The operating frequency of the receiver can be selected in 0.5-kHz steps from 190 to 1749.5 kHz.
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